AN ENGINEERED CLAY SOIL SYSTEM USING FUNCTIONAL …

The Pennsylvania State University

The Graduate School

Department of Civil and Environmental Engineering

AN ENGINEERED CLAY SOIL SYSTEM USING FUNCTIONAL

POLYMERS

A Dissertation in

Civil Engineering

by

Sungho Kim

copy 2011 Sungho Kim

Submitted in Partial Fulfillment

of the Requirements

for the Degree of

Doctor of Philosophy

December 2011

ii

The dissertation of Sungho Kim was reviewed and approved by the following

Angelica Maria Palomino

Assistant Professor of Civil and Environmental Engineering

Dissertation Advisor

Chair of Committee

Mian C Wang

Professor Emeritus of Civil and Environmental Engineering

James H Adair

Professor of Material Science and Engineering

Coray M Colina

Associate Professor of Material Science and Engineering

Peggy A Johnson

Professor of Civil and Environmental Engineering

Head of the Department of Civil and Environmental Engineering

Signatures are on file in the Graduate School

iii

ABSTRACT

Soil modification is widely accepted to improve soil properties in the field of

geotechnical and geoenvironmental engineering In the case of clay soil it is well known that the

clay fabric determines properties of the soil such as permeability shear strength and

compressibility Although clay fabric has successfully been modified using polymers they are

typically utilized as a static modification That is no further structural modification is expected

due to the irreversible interactions between the polymer and clay particles In this study

responsive polymers those for which conformational behavior is affected by the surrounding

environment such as pH and ionic strength are used as a clay fabric modifier such that the final

structures are ldquotunablerdquo Three studies were conducted to investigate (1) composite synthesis of

clay and responsive polymer (2) tunability of the composites at the meso-scale and (3)

computational studies of the tunability

First synthesis of bentonite-polyacrylamide nanocomposites was performed by

investigating variables such as synthesizing temperature clay content polymer molecular weight

pH and clay-to-polymer volume ratio X-ray diffraction was used to characterize effects of each

variable on the synthesis of nanocomposites with intercalated structure Optimum conditions for

the greatest quantity of intercalated structure were found at clay content of 0001 synthesis with a

low molecular weight polymer and clay-to-polymer volume ratio of 2

Second tunability of the synthesized nanocomposites was investigated using step-by-step

laboratory experiments (1) dynamic light scattering was used to confirm pH-responsiveness of

polyacrylamide in a bulk solution (2) spectroscopic ellipsometry was used to explore validity of

the pH-responsiveness after adsorption on a surface and (3) meso-scale characterization such as

specific surface area measurement swelling tests and pressurized permeability tests were

iv

performed to investigate whether the micro-scale conformational changes of the polymer lead to

modification of meso-scale engineering properties of clay-polymer composites

Thirdly a computational study on tunable behavior of the nanocomposites was performed

Since the conducted laboratory tests provide indirect insight into the behavior of the

nanocomposites a computational study provides further evidence supporting the tunable

characteristics of the nanocomposites Results from dissipative particle dynamics were in a good

qualitative agreement with experimental data

v

TABLE OF CONTENTS

LIST OF FIGURES viii

LIST OF TABLES xi

ACKNOWLEDGEMENTS xii

INTRODUCTION 1

11 Motivation 3

12 Objectives 4

13 Hypothesis 5

14 Expected Contributions 5

LITERATURE REVIEW 7

21 Nature of Montmorillonite 7

22 Responsive Polymers 14

23 Polyacrylamide-Montmorillonite Interactions and Associations 18

24 Synthesis of Clay-Polymer Nanocomposites 22

25 Characterization of Clay-Polymer Nanocomposites 24

251 X-ray Diffraction 24

252 Spectroscopic Ellipsometry 24

26 Computer Simulation 25

261 Overview 25

262 Dissipative Particle Dynamics 28

SYNTHESIS OF TUNABLE CLAY-POLYMER NANOCOMPOSITES 32

31 Introduction 32

32 Experimental Study 33

321 Materials 33

322 Synthesis of Clay-Polymer Nanocomposites ndash Solution Intercalation 36

323 Mixing and Drying Temperatures 37

324 Analysis Techniques 38

vi

33 Results and Discussion 39

331 Influence of Mixing and Drying Temperatures 40

332 Mineral Dissolution 43

333 Nanocomposite Synthesis Optimization 45

335 Dominant Factor for Intercalated Structure Formation 48

34 Conclusions 49

MANUPULATION OF SYNTHESIZED CLAY-POLYMER NANOCOMPOSITES 51

41 Introduction 51

42 Materials 53

421 Clay Minerals 53

422 Polyacrylamide 55

423 Synthesis of CPN and Microcomposites 56

43 Micro-Scale Characterization 57

431 Dynamic Light Scattering 58


44 Meso-Scale Characterization 65

441 Specific Surface Area 66

442 Swelling Test 69

443 Hydraulic Conductivity Measurement 73

45 Linkage of Micro-Scale Behavior to Meso-Scale Property 79

46 Conclusions 82

COMPUTER SIMULATION 84

51 Introduction 84

52 Mapping of Length- and Time Scales 85

53 Polyacrylamide in an Aqueous Solution 87

54 Polyacrylamide Adsorbed on a Clay Particle 92

55 Interlayer Spacing Manipulation 95


vii

57 Conclusions 103

CONCLUSIONS 105

Future Work 107

REFERENCES 109

Appendix A Example Calculation for Clay-to-Polymer Volume Ratio 123

Appendix B Pressurized Permeability 124

Appendix C DPD Equilibration 125

Appendix D Scaling of Simulated system 127

VITA 128

viii

LIST OF FIGURES

Figure 21 Mineral composition of dry Na+-montmorillonite used in the study Violet-colored

circles denote an exchangeable cation Na+ Basal spacing in the absence of the exchangeable

cations is 0913 nm for dry clay (van Olphen 1977) The thickness of a layer is 0654 nm

obtained using X-ray diffraction (Brindley and Brown 1980) 9

Figure 22 Electrical potential (Vx) of double layer compiled from Israelachvili (1991) Stumm

(1992) Santamarina et al (2001) and Mitchell (1993) 11

Figure 23 Hydrolysis reaction of polyacrylamide under basic conditions Compiled from

Barvenik (1994) Kurenkov (1997) and Myagchenkov and Proskurina (2004) 16

Figure 24 Hydrolysis reaction of cationic polyacrylamide under basic conditions Compiled

from Aksberg and Wagberg (1989) 17

Figure 25 Conformations for nonionic PAM under various pH and ionic strength conditions

(Michaels 1954 Klenina and Lebedeva 1983 Al-Anazi and Sharma 2002 Besra et al 2004)

Cyan and red monomers denote neutral monomer and charged monomer respectively Images

obtained from computer simulations (dissipative particle dynamics) 18

Figure 26 Schematic of various clay-polymer composites (a) phase-separated (b) intercalated

and (c) exfoliated structures 21

Figure 27 Time-length scale plot illustrating various computational methods at relevant time

and length scales Also shown are the basic interaction units in each method 26

Figure 28 Schematic of coarse-graining on (a) a polyacrylamide chain and (b) a Mt particle

The smaller spheres represent atoms the larger yellow and blue spheres are coarse-grained beads

Bond length (L) and bond angle (A) of the coarse-grained beads are also shown 28

Figure 31 Basal spacings for bentonite-nPAM nanocomposites synthesized at (a) 20degC (b)

60degC and (c) 85degC mixing temperatures 41

Figure 32 Basal spacings for bentonite-nPAM nanocomposites synthesized at 20degC and 110degC

drying temperatures with (a) low molecular weight PAM and (b) high molecular weight PAM 42

Figure 33 Si-NMR spectra for clay-polymer nanocomposites synthesized with (a) unadjusted

polymer solution and pH-adjusted polymer solutions (b) pHasymp4 and (c) pHasymp11 Al-NMR spectra

for clay-polymer nanocomposites synthesized with (d) unadjusted polymer solution and pH-

adjusted polymer solutions (e) pHasymp4 and (f) pHasymp11 44

Figure 34 XRD diffractogram for clay-polymer nanocomposites synthesized with (a)

unadjusted polymer solution and pH-adjusted polymer solutions (b) pH 4 and (c) pH 11 M

denotes a typical peak for Mt 45

ix

Figure 35 Impact of clay content on quantity of montmorillonite intercalated with PAM XRD

intensity was obtained from a peak corresponding to basal spacings greater than 145 Aring Error

bars were plotted based on the calculated standard deviation of three measured values 46

Figure 36 Impact of clay-to-polymer volume ratio on quantity of montmorillonite intercalated

with PAM XRD intensity was obtained from a peak corresponding to basal spacings greater than

145 Aring Error bars were plotted based on calculated standard deviation of three measured values

48

Figure 41 Scanning electron microscopy images for (a) bentonite and (b) CPN synthesized

using bentonite and PAM 57

Figure 42 Scanning electron microscopy images for (a) kaolinite and (b) microcomposite

synthesized using kaolinite and PAM 57

Figure 43 Hydrodynamic radius of montmorillonite and nPAM as a function of pH 59

Figure 44 Schematic of spectroscopic ellipsometry apparatus 62

Figure 45 Real part of the complex dielectric function spectra ( = 1 + i2) for PAM in

solutions with pH = 3 6 and 115 Also shown is 1 for H2O 63

Figures 46 (a) PAM thickness and (b) change in thickness as functions of time in solutions with

pH = 3 6 and 115 63

Figure 47 MB specific surface area of (a) microcomposites and (b) CPN as a function of pH

Clay-to-polymer volume ratio for (a) and (b) was 625 and 2 respectively 68

Figure 48 Swelling ratio of (a) microcomposites and (b) CPN as functions of pH and time The

dashed lines indicate the swelling ratios for the untreated (no polymer) materials 71

Figure 49 Schematic of pressurized permeability test apparatus with a picture of permeability

cell 75

Figure 410 Permeability of kaolinite-PAM microcomposites as a function of pH (a) gel-form

and (b) powder-form 76

Figure 411 Permeability of CPN as a function of pH (a) gel-form and (b) powder-form 78

Figure 412 Behavior comparison between hydrodynamic radius and adsorbed layer thickness of

PAM Hydrodynamic radius was measured using dynamic light scattering and adsorbed PAM

layer thickness was obtained from spectroscopic ellipsometry 80

Figure 413 Behavior comparison between adsorbed PAM layer thickness and swelling ratio

Adsorbed PAM layer thickness was obtained from spectroscopic ellipsometry and swelling ratio

was measured using water absorbency tests 81

Figure 51 ltRg2gt12 of the simulated polymer in water as a function of (a) charge fraction and (b)

pH 90

x

Figure 52 ltRg2gt12 vs simulation time for PAM with charge density of (a) 025 and (b) 033 91

Figure 53 (a) ltRg2gt12 of the simulated polymer adsorbed on a clay surface and (b) the polymer

layer thickness as a function of pH 93

Figure 54 Trajectories of the polymer and the clay surface (a) initial configuration and final

configurations with charge density of (b) 00 (c) 01 (d) 0143 (e) 02 (f) 025 (g) 033 (h)

05 and (i) 08 Cyan red yellow and black beads denote neutral monomer charged monomer

neutral clay and charged clay 94

Figure 55 (a) ltRg2gt12 of the simulated polymer sandwiched between two clay layers and (b) the

interlayer spacing as a function of pH at clay-to-polymer volume ratio 4 96

Figure 56 Trajectories of the polymer and the clay surfaces at clay-to-polymer volume ratio 4

(a) initial configuration containing two clay surfaces a PAM molecule and water and final




Figure 57 (a) ltRg2gt12 of the simulated polymer sandwiched between two clay layers and (b)

the interlayer spacing as a function of pH at clay-to-polymer volume ratio 2 100

Figure 58 Swelling ratio and simulated interlayer spacing for CPN as a function of solution pH

Diamond and square symbols denote the swelling ratio and the simulated interlayer spacing

respectively The CPN was synthesized at clay-to-polymer volume ratio 2 102

Figure C1 ltRg2gt12 vs simulation time for PAM with charge density of (a) 00 (b) 01 (c)

0143 (d) 02 (e) 025 (f) 033 (g) 05 and (h) 08 at clay-to-polymer volume ratio 4 126

Figure D1 Schematic of simulated components used in this study (a) a DPD bead (b) a PAM

molecule and (c) a Mt surface 127

Figure D2 Simulated interlayer spacing results (a) in simulation unit (dimensionless) and (b) in

real unit (nm) 127

xi

LIST OF TABLES

Table 31 Chemical composition of the sodium bentonite used in this study (Supplier data) 35

Table 32 Properties of the sodium bentonite used in this study 35

Table 33 Characteristics of polyacrylamides used in this study 35

Table 34 Test matrix and resulting basal spacing with XRD intensity 40

Table 41 Chemical composition of clay minerals used in this study 54

Table 42 Properties of clay materials used in this study 54


Table 51 Scaling relations used in this study (Fuchslin et al 2009) 86

Table 52 DPD parameters used in this study 88

Table 53 Force constants α used in this study 88

xii

ACKNOWLEDGEMENTS

Throughout my work on this PhD research I have been fortunate to have been helped by

many people making the completion of this research possible Of these people the first I would

like to appreciate is my advisor Dr Angelica Palomino She gave me the flexibility in selecting

any topic which I was interested in allowing me to in-depth study the fundamental study I have

spent the last 3 years working on I would like to thank her also for her support guidance

availability and insights Since I met Dr Palomino my advice to students looking for a graduate

advisor has simply been ldquoFind someone like Dr Palominordquo

I would like to thank all of my committee members Dr Mian Wang Dr James Adair

and Dr Coray Colina who helped guide me when I needed extra assistance They have spent a

great deal of time discussing ideas with me and keeping me on the right track

I owe many thanks to the following people who helped me accomplish this research Dr

Nicholas Podraza and Mr Michael Motyka helped me conduct spectroscopic ellipsometry

Professor Evangelos Manias helped me develop idea of this research and shared his expertise on

clay-polymer nanocomposites and computer simulations Dr Martin Lisal Dr Gregory Larsen

and Ms Kristin Patterson shared their knowledge on computer simulations Ms Nicole

Wondering with an expertise of X-ray diffraction shared a lot of knowledge and techniques with

me Ms Maria Klimkiewicz helped me do scanning electron microscopy Mr Daniel Fura a

technical support supervisor of CITEL helped me perform all laboratory experiments

I acknowledge the National Science Foundation (NSF) that provided funding for a part of

this study This work is as a result of partial support from the NSF under grant 1041995

My family has provided me with unconditional support and advice which have made my

completion of this work possible My wife Soojin Ahn has always been willing to lend an ear

Thank you all for all of your help and friendship

Chapter 1

INTRODUCTION

Not all soils inherently have desirable geotechnical and geoenvironmental engineering

properties Physical andor chemical processes are often manipulated to obtain a target

performance of soil systems For example grains can be added to grains with different

morphologies as in diatom-kaolin clay mixtures to influence the mixture flocculation liquid

limit and plasticity water retention and even solubility (Palomino et al 2011) It is well known

that clay particle arrangement the so-called clay fabric varies with the bulk fluid chemistry such

as pH ionic concentration and temperature (van Olphen 1977 Theng 1979 Mitchell 1993

Lagaly 2006) Clay fabric alteration leads to changes in macro-scale clay properties such as

permeability (Mitchell 1956 Suarez et al 1984) shear strength (Sridharan and Prakash 1999)

compressive strength (Nasser and James 2006) and compressibility (Gajo and Maines 2007) In

addition the use of polymer at different concentrations molecular weights andor ionic types

alters the bulk fluid chemistry manipulating clay fabric (Kim and Palomino 2009) Polymer-

treated clay composites so-called clay-polymer composites may lead to enhancements of overall

clay material characteristics such as shear strength permeability clay swelling and contaminant

barrier properties (van Olphen 1977 Theng 1979 Hjelmstad 1990 Lo et al 1997 Inyang and

Bae 2005) While each of these approaches improves the soil properties these methods are

essentially permanent that is irreversible Irreversible interactions of polymer molecules with

clay mineral surface limits further modifications of the clay-polymer composites (Nadler et al

1992)

The use of responsive polymers in which the conformation varies with external

environment triggers will lead to a new family of clay-polymer composites Since the

conformation of a given responsive polymer varies with the external environment for example

2

bulk solution pH responsive polymers may provide the capacity to modify in-situ properties of

resulting clay-polymer composites after polymer placement That is the interlayer andor

interparticle spacing of composites synthesized from responsive polymers can be manipulated

through changes in the surrounding fluid pH ionic concentration temperature and electric field

For example clay-polymer composites synthesized using a pH responsive polymer may be

capable of further modification by exposing the composites to alternate pH conditions

Furthermore the use of water-soluble responsive polymer can have the potential for large-scale

in-situ modification due to minimum energy demand In order to maximize the potential for

interlayer andor interparticle spacing modification the optimized design of these composites is

an intercalated structure in which polymer molecules are adsorbed onto both the particle surface

and interlayer surface Thus both interparticle and interlayer distances of the final composite

have the ability to be modified through exposure to various pH

Although soil modification using polymers or surfactants have been previously

investigated (Gardner and Arias 2000 Bhardwaj et al 2007 Story et al 2009 Young et al

2009) thus far responsive polymers have not been addressed for this purpose Efforts to produce

a material with controllable morphology have recently been reported with the use of responsive

polymers ie polymers which are responsive to external environmental conditions such as pH

(Feil et al 1992 Xia et al 2006) ionic strength (Wu and Shanks 2003) temperature (Bae et al

1990) and electrical potential (Kim et al 2006) Some pH-responsive polymers such as

polyacrylamide and poly(acrylic acid) have the added benefit of high solubility in water The

combination of pH- or ionic concentration responsiveness and high solubility is advantageous for

producing large-scale quantities of clay-polymer composite material with the ability to be

ldquotunablerdquo in-situ thus creating a novel type of engineered soil

In spite of the considerable number of studies of clay-polymer composites clay

intercalation by polymer is not yet fully understood Due to many factors affecting the process

3

and difficulties of developing tools capable to monitor the process quantifying final morphology

and properties of the final clay-polymer composite is very challenging In addition

characteristics of clay minerals and the interactions responsible for meso-scale properties

occurring at the length scales of monomers approximately a billionth of a meter limit probing

with current experimental techniques Thus computer simulation and modeling may play an

ever-increasing role in designing and predicting material properties and designing such

experimental work For clay-polymer composites computer simulation and modeling are

especially useful in addressing the thermodynamics and kinetics of the formation of composites

the hierarchical characteristics of the structure and dynamics the dependence of polymer

rheological behavior on the addition of clay particles and the molecular origins of the

reinforcement mechanisms

11 Motivation

The motivation for this study can be summarized as follows

(1) Irreversible interactions of polymer with clay limits further modifications of clay-

polymer composites

(2) Commonly used techniques including melt intercalation and in-situ intercalation to

produce clay-polymer composites with intercalated structure demands extra energy

thus limits large-scale production which is necessary for geotechnical and

geoenvironmental applications

(3) With current experimental technologies it is very challenging to quantitatively

characterize polymer molecules in the interlayer space of clay minerals

4

12 Objectives

Although many studies of soil modification with the use of polymers and efforts to

produce a material with controllable morphology have been previously addressed a study of

large-scale clay modification with the use of responsive polymers has not been reported Micro-

andor nano-level conformational changes of responsive polymers as a function of external

environment triggers may result in changes in micro- and meso-scale properties In addition the

use of water-soluble polymers may provide the potential for in-situ large-scale production This

work includes the use of water-soluble responsive polymers as a viable tool for creating a new

family of clay-polymer composites The optimum condition for creating clay-polymer

composites while maximizing the amount of intercalated structure formation was investigated

experimentally Once the optimum conditions were found further experimental and

computational investigations were conducted to determine whether or not the controllable

characteristics of the responsive polymer results in changes in micro- and meso-scale properties

of the clay-polymer composites ie ldquotunablerdquo clay-polymer nanocomposites

The objectives of this study are (1) to create ldquotunablerdquo clay-polymer nanocomposites

using an expandable clay (montmorillonite) and a water-soluble responsive polymer

(polyacrylamide) and to develop an optimized procedure for the future large-scale production of

in-situ modifiable engineered clay soils (2) to link the micro-scale response of the polymer in

the synthesized clay-polymer composites to the meso-scale properties of the system such as

specific surface area swelling potential and permeability and (3) to perform a computational

analysis supporting the experimental findings X-ray diffraction will be used to investigate the

formation of intercalated structure Nuclear magnetic resonance will be used to explore the

effects of strong acidic and basic solutions on the mineral dissolution Dynamic light scattering

and spectroscopic ellipsometry will be used to characterize the controllable morphology of the

clay-polymer composites at the micro-scale Specific surface area swelling potential and

5

hydraulic conductivity will be measured to characterize the controllable morphology at the meso-

scale Coarse-grained atomistic computer simulation technique will be utilized to support the

experimental findings

13 Hypothesis

This study is about synthesizing a new family of clay-polymer composites characterizing

and exploring micro- and meso-scale behavior of the composite material The specific questions

to be addressed in this study are

(1) Is it possible to synthesize a new family of clay-polymer composites ldquotunablerdquo clay-

polymer nanocomposite using an expansive clay and a responsive polymer If so

what is the optimum condition for the synthesis

(2) Can tunability of the new clay-polymer composite be characterized using current

experimental techniques such as spectroscopic ellipsometry

(3) Does the tunability at the micro-scale result in property changes at the meso-scale

(4) Can computer simulation support the experimental findings

14 Expected Contributions

Clay-polymer composites have proven effective for improving material properties

However the use of polymer has been limited in the field of geotechnical and geoenvironmental

engineering for many reasons including cost inefficiency and difficulties in handling Since this

study shows a way to solve the aforementioned problems it is expected that the use of polymer

materials in the geotechnical and geoenvironmental engineering will become more common In

particular it was found that an engineered clay soil with an ability for further modification has

the potential for many state-of-the-art applications by showing cost-effective procedures for

6

synthesis micro- and meso-scale characterizations and a way of overcoming limitations of

quantitative characterization ie introduction of computer simulation

7

Chapter 2

LITERATURE REVIEW

Much can be learned from the existing literature about the nature of clays and clay

surfaces polymers and even the interaction between the two materials Yet very little is known

about the behavior of responsive clay-polymer composites Systematic studies will be carried out

to investigate clay-polymer composite swelling behavior the conformational behavior of a

selected polymer interactions between the clay and polymer composite synthesizing techniques

and meso-scale computer simulation techniques Topics addressed in this chapter include (1) the

nature of montmorillonite (2) the concept of responsive polymers (3) polyacrylamide-

montmorillonite interactions and associations (4) preparation and (5) characterization of clay-

polymer composites and (6) meso-scale computer simulation

21 Nature of Montmorillonite

Montmorillonite (Mt) is a member of the smectite mineral group It has a crystalline

structure consisting of two silica tetrahedral sheets and one aluminummagnesium octahedral

sheet (21 layered phyllosilicate) The tetrahedral sheets and octahedral sheet are strongly held

together by shared oxygen atoms ndash covalent bonds ndash forming a single layer The thickness of the

layers is on the order of 1 nm and aspect ratios are typically 100 to 1500 Various cation

substitutions such as Si4+ by Al3+ in tetrahedral sheets and Al3+Fe3+ by Mg2+Fe2+ in octahedral

sheets ie isomorphic substitution can occur leading to a net negative charge on the layers (van

Olphen 1977 Brindley and Brown 1980 Newman 1987) The resulting charges are

counterbalanced by exchangeable cations such as Na+ K+ Ca2+ Mg2+ and organic ions While

some charge balancing cations are located on the external crystallite surface the majority of

exchangeable cations are found in the interlayer space (Giannelis et al 1999 Luckham and Rossi

1999)

8

Mt has the idealized structural formula My+∙nH2O(Al2-yMgy)Si4O10(OH)2 where M is a

monovalent charge compensating cation in the interlayer and y is the degree of isomorphic

substitution ranging from 50 to 130 represented as the cation exchange capacity (CEC cmolkg)

(van Olphen 1977 Brindley and Brown 1980 Giannelis et al 1999 Ray and Okamoto 2003)

The mineral composition of Mt compensated with sodium ions Na033[(Al167Mg033)Si4O10(OH)2]

is shown in Figure 21 Weak van der Waals attraction forces as well as a high repulsive potential

on the layer surface induced by isomorphic substitution allow water molecules and cations to

penetrate such that the interlayer spacing expands This is the basis for swelling behavior (van

Olphen 1977 Israelachvili 1991 Mitchell 1993)

Swelling behavior consists of two stages (van Olphen 1977) (1) crystalline or short-

range swelling and (2) osmotic or long-range swelling When dry Mt is first exposed to moist

conditions the interlayer cations become hydrated with water molecules The layers may

separate from 96Aring up to 22Aring (Theng 1979) The adsorption energy of the water layers on the

clay surface is the driving force in this stage of swelling The swelling behavior depends on the

nature of the interlayer cations such as the capacity of cations to retain the polar molecules within

the interlayer space and the location of the layer charge (van Olphen 1977 Newman 1987

Berend et al 1995 Whitley and Smith 2004 Ferrage et al 2005 Meunier 2005 Douillard et

al 2007) For example the interlayer spacing for Na+-montmorillonite increases from 96 Aring to

125 Aring when hydrated with one water layer under low water content to 156 Aring when hydrated

with two water layers and to 188 Aring when hydrated with three water layers under high water

content (Berend et al 1995 Chang et al 1995 Ferrage et al 2005)

On the other hand swelling does not occur when the layer charge is zero where no

cation-hydration occurs or when the layer charge is too high resulting in large electrostatic

attraction forces which prevent the penetration of water molecules (Meunier 2005)

9




obtained using X-ray diffraction (Brindley and Brown 1980)

Mt saturated with polyvalent cations typically swells less than when saturated with monovalent

cations because electrostatic attraction between a polyvalent cation and layer surface is large

enough to offset the double layer repulsion (Berend et al 1995 Luckham and Rossi 1999 Salles

Si

O

Al

Mg

Na

basal

spacing

096 nm

to ~ infin

Octahedral

sheet

Tetrahedral

sheet

Interlayer

space

Tetrahedral

sheet

10

et al 2007) In addition the electrostatic forces between the divalent cations and the layer

surface are greater than hydration forces of the divalent cations (Ashmawy et al 2002)

Mt saturated with small monovalent cations such as Li+ and Na+ can absorb more water

Osmotic forces derived from the relatively high ionic concentrations between the layers allow

water molecules to keep penetrating and thus leads to osmotic swelling (Swartzen-Allen and

Matijevic 1974 van Olphen 1977) Due to the difference in hydration energy swelling

increases for Mt containing counterions in the order of Li+ gt Cs+ Na+ gt Rb+ gt K+ (Newman

1987 Berend et al 1995 Hensen et al 2001 Salles et al 2007) This osmotic stage of swelling

is accompanied by large volume changes ndash in excess of 40Aring ndash of the interlayer spacing and is

limited by frictional forces of the particle surface due to the formation of edge-to-face particle

associations (van Olphen 1977 Theng 1979) As water content increases the layers swell

laterally as well as longitudinally (Fukushima 1984)

Near the mineral surface hydrated counterions are attracted to the net charge of the layer

surface according to Coulombic attraction These counterions diffuse away from the mineral

surface due to water polarity and thermal agitation The diffusion range is limited by the

attraction force between the particle or layer surface and the hydrated counterion and by the

electrical potential of the particle or layer The counterion concentration decreases to the bulk

fluid concentration as a function of distance from the surface The electrical double layer consists

of the Stern layer and the Gouy-Chapman diffuse layer as shown in Figure 22 The outer

boundary of the Gouy-Chapman diffuse layer is not well-defined (van Olphen 1977 Stumm

1992) The magnitude of surface charge is represented as the Stern potential and zeta potential

The Stern potential is represented by the pH value at which the total net surface charge is zero

while the zeta potential is depicted as zero electrophoretic mobility of a particle in an electric

field (Sposito 1998) The difference between Stern potential and zeta potential implies the

amount of diffuse ions entrapped within the shear plane of the electric double layer For example

11


(1992) Santamarina et al (2001) and Mitchell (1993)

the experimentally determined value of surface potential for one type of Mt is approximately 128

mV the zeta potential is found to be 78 mV and the distance from the surface to the shear plane

is 05 nm (Theng 1979) The thickness of the double layer (1κ in meters) depends on

(2)

(3)

(1)

Surface potential

Vst (Stern potential)

ζ (zeta potential)

Vst e Vx = Vstmiddote-x

κ (double layer thickness) distance x

(1) inner sphere complexes

(2) outer sphere complexes

(3) diffuse ion swarm

shear

plane

Stern

layer

Gouy-Chapman diffuse layer

12

permittivity of the surrounding fluid temperature bulk fluid concentration and ionic valence

(Stumm 1992 McBride 1994)

2

0

2

0

2

1

zc

T

Ne

k

av

B

where kB is Boltzmannrsquos constant (138 x 10-23 JK) ε0 is the permittivity of free space (8854 x

10-12 C2J-1m-1) e is the electron charge (1602 x 10-19 C) Nav is Avogadrorsquos number (6022 x 1023

mol-1) ε is the dielectric constant of the bulk fluid (785 for water at 25degC) T is absolute

temperature (K) c0 is bulk fluid (electrolyte) concentration (molm3) and z is the ion valence

Random movements of hydrated counterions in and out of the double layer induces a change in

the thickness as a function of thermal agitation and the availability of counterions (van Olphen

1977 Hunter 1993 Santamarina et al 2001)

Clay surface charge density consists of (Sposito 1989 Stumm 1992 Sposito 1998) (1)

permanent structural charges (σ0) resulting from isomorphic substitution or broken bonds in the

clay lattice (2) net proton charges (σH) due to protonationdeprotonation ie pH-dependent (3)

inner-sphere surface complex charges (σIS) and outer-sphere surface complex charges (σOS) and

(4) adsorbed ions in the diffuse double layer (σD) which have a similar mobility to the ions in the

bulk fluid The inner-sphere surface complexes include no water molecules between the clay

surface and the cation while the outer-sphere surface complexes contain at least one water

molecule in between Protonation and deprotonation of the mineral surface occurs through

potential determining ions such as H+ and OH- Other ions may form inner- and outer-sphere

complexes through adsorption Cation adsorption is especially significant because it alters the

surface charge on O2- termination sites depending on the concentration valence and size of the

ions Charge on a silica tetrahedral basal face (Si4O10) of smectite minerals can vary

approximately from 03 to 065 ie one O2- termination site every 028 ~ 06 nm2 (Meunier

2005) The charge can be calculated as (Zelazny et al 1996 Meunier 2005)

13

Charge = CEC (cmolkg) x mass of half unit cell (g) x 10-5

For example if a Mt has half unit cell formula Na033[(Al167Mg033)Si4O10(OH)2] and CEC=808

cmolkg layer charge of the mineral is 03

In 21 minerals such as Mt the permanent structural charge (σ0) is significant due to a

large amount of isomorphic substitution Since the permanent structural charges are pH-

independent all pH-dependent charges are typically on the particle edges where hydroxyl groups

such as Al-OH12- and Si-OH are dominant due to broken bonds of the tetrahedral and octahedral

layers While Mt theoretically has pH-dependent charges at the particle edges these charges

represent less than 5 of the total surface charge (Borchardt 1989) In addition to the particle

edges particle faces were also reported to be pH-dependent representing as much as 20 of the

face surface charge (Schindler 1981 Mohan and Fogler 1997)

The point of zero charge (PZC) is defined as pH value where total net surface charge (σP

= σ0 + σH + σIS + σOS) is zero (ie Stern potential is zero) The isoelectric point (IEP) is reached

when the electrophoretic mobility of a particle in an electric field is zero (ie zeta potential is

zero) Due to the diffuse nature of the ion swarm the PZC is typically not equal to the IEP

(Sposito 1998) Both PZC and IEP of a clay particle depend on the availability of OH-

termination sites along the particle surface fluid pH and the dominant counterion valence and

concentration in the fluid (Stumm 1992 Santamarina et al 2001) The presence of significant

permanent structural charges in Mt results in IEP less than pH 25 (Parks 1967 Drever 1997) or

even undetected IEP (Nishimura et al 1994 Tombacz et al 2001) Therefore the surface

charge of 21 mineral particles may remain negative even at very low pH

In general pore fluid chemistry such as pH and ionic concentration significantly affects

Mt particle arrangement (van Olphen 1977 Lagaly 1989 Mitchell 1993 Santamarina et al

2002a) In pH ranging from 4 to 11 edge-to-edge flocculation is observed at NaCl

concentrations greater than 5x10-3 molL and face-to-face aggregation is observed at NaCl

14

concentration greater than 025~03 molL (Rand et al 1980 Chen et al 1990) At pH below 4

the particle edges become positively charged while the particle faces still remain negatively

charged inducing electrostatic attraction between the edges and faces ie edge-to-face

flocculation (Lagaly 1989 Mohan and Fogler 1997) The edge-to-face flocs remain unsettled in

Mt suspensions which differs from that in kaolinite suspensions

When exposed to extreme pH conditions clay particles are subjected to irreversible

dissolution affecting the structure and structural charges (σ0) (Carroll and Starkey 1971 Shinoda

et al 1995 Zysset and Schindler 1996 Santamarina et al 2002a Steudel et al 2009) At low

pH the protonation of OH- in the octahedral layer and of O2- in the tetrahedral layer results in a

release of SiO2 At high pH the deprotonation of Si-OH and the formation of Si-O- in the

tetrahedral layer results in a release of Si The dissolution behavior is mainly observed at the

edge sites and the dissolution rate depends on both pH and ionic concentration Si dissolution

rates range from 3x10-7 to 2x10-6 molgmiddoth at pH 1 (Zysset and Schindler 1996) In addition to the

dissolution behavior a solution with high pH and ionic concentration may convert smectite into

illite at room temperature (Whitney 1990 Bauer and Velde 1999)

22 Responsive Polymers

Polymers are large molecules macromolecules composed of smaller units called

monomers Polymer characteristics vary with the arrangement of those monomer units andor the

various types of functional groups resulting in unique properties (Painter and Coleman 1997)

For example the chain conformation of a pH-responsive polymer such as poly(acrylic acid) or

polyacrylamide containing either an acidic (COOH) or a basic (NH2) functional group in the

polymer network varies with bulk solution pH (Michaels and Morelos 1955 Feil et al 1992

Chen and Hoffman 1995 Al-Anazi and Sharma 2002 Liu et al 2008)

15

Responsive polymers are the result of efforts to produce a material with controllable

morphology Responsive polymers are responsive to external environmental conditions such as

pH (Siegel and Firestone 1988 Brannon-Peppas and Peppas 1991 Feil et al 1992 Gudeman

and Peppas 1995 Al-Anazi and Sharma 2002 Xia et al 2006) ionic strength (Flory 1953

Gudeman and Peppas 1995 Al-Anazi and Sharma 2002 Wu and Shanks 2003) temperature

(Bae et al 1990 Park and Hoffman 1992) electric potential (Tanaka et al 1982 Kim et al

2006) and photo-irradiation (Suzuki and Tanaka 1990) Clay-polymer composites synthesized

with expansive clay (montmorillonite) and responsive polymer (polyacrylamide) were also

reported to show such controllable morphologies due to the responsiveness of polymer (Gao and

Heimann 1993)

The conformation of such responsive polymers varies with external environment triggers

Polyacrylamide polymer chains tend to have coiled conformation at pH below 105 and to have

extended conformation at pH above 105 (Besra et al 2004) Poly(acrylic acid) polymer chains

tend to have coiled conformation at pH below 425 and to have extended conformation at pH

above 425 (Al-Anazi and Sharma 2002) These pH-responsive polymers have the added benefit

of high solubility in water The combination of pH- or ionic concentration responsiveness and

high solubility is advantageous for producing large-scale quantities of clay-polymer composite

material with the ability to be ldquotunablerdquo in-situ thus creating a novel type of engineered soil

Polyacrylamide (PAM) is a widely used water-soluble polymer which is synthesized by

free radical polymerization of acrylamide derived from acrylonitrile by either bioconversion or

catalytic hydrolysis (Kulicke et al 1982 Brandrup and Immergut 1989 Barvenik 1994

Kurenkov 1997 Huang et al 2001 Wu and Shanks 2004) Polyacrylamide is a linear

amorphous odorless hard glassy white polymer with a very low toxicity The preferential

reactivity ratios of acrylamide allow a wide range of molecular weights further functionalizations

and charge densities A colorless crystalline acrylamide contains two functional groups a

16

a

CH

NH2

O = C

CH2

reactive double bond and an amide group The amide group is reactive in changing the ionic

character or in cross-linking the polymer A polyacrylamide solution generally undergoes

reaction characteristics of an aliphatic amide group most importantly hydrolysis

Hydrolysis can occur under acidic or basic conditions and is reversible (Kheradmand et

al 1988 Kurenkov 1997) The acidic hydrolysis reaction of the amide group is very slow On

the other hand basic hydrolysis of polyacrylamide is a rapid reaction and incorporates acrylate

groups (COO-) into macromolecules as shown in Figure 23 The degree of hydrolysis is

influenced by temperature reaction time and the concentration of salts such as NaCl and KCl

The maximum degree of hydrolysis is 70~80 for polyacrylamide due to reduced reactivity of

the amide groups and depends on the effects of the neighboring carboxylate groups as well as the

conformation of polyacrylamide (Kurenkov 1997 Huang et al 2001) The rate of hydrolysis for

cationic polyacrylamides increases as pH or temperature increases and as the mole ratio of

cationic functional groups decreases (Aksberg and Wagberg 1989) Charge density on cationic

polyacrylamide decreases as the hydrolysis reaction (Figure 24) progresses

+ bNaOH rarr + bNH3


Barvenik (1994) Kurenkov (1997) and Myagchenkov and Proskurina (2004)

CH2

a-b

CH

NH2

O = C

CH2

b

CH

Na+

O = C

O-

17

a

CH

NH2

O = C

CH2 CH2

b

CH

N+

O = C

O

(CH2)2

(CH3)3

Cl-

+ OH- rarr +


from Aksberg and Wagberg (1989)

When a solution of polyacrylamide with molecular weight above 1 x 106 is kept at room

temperature the intramolecular hydrogen bonds begin to collapse and the polymer degrades The

macromolecules undergo conformational changes to a more compact flexible coil conformation

having a smaller hydrodynamic volume thus decreasing the overall viscosity (Kulicke et al

1982) Three types of degradation may occur in aqueous solution of polyacrylamide (Kulicke et

al 1982 Huang et al 2001) (1) thermal degradation which occurs slightly at 50˚C and

significantly at 75˚C (2) mechanical degradation for which the viscosity decreases with

increasing high speed stirring of the aqueous polymer solution and (3) oxidative degradation

which occurs depending on pH The degradation can be facilitated by free radicals ionizing

radiation light heat shear and stirring speed of aqueous polyacrylamide solution Careful

handling of the solution as well as the addition of sodium nitrile or thio compounds can inhibit

the degradation of polymers (Kulicke et al 1982 Kurenkov 1997 Huang et al 2001)

PAM is pH-responsive polymer due to its bias hydrolysis behavior under acidic or basic

conditions The hydrolysis reaction of the amide group on PAM molecules occurs very slowly

under acidic conditions while it occurs rapidly under basic conditions The hydrolysis reaction

incorporates acrylate groups (COO-) introducing negative charges on the molecules The

repulsive forces between hydrolyzed groups repel monomer units of PAM expanding the whole

CH2

n-m

CH

NH2

O = C

CH2

m

CH

Na+

O = C

O- n-m

CH2 CH2

OH N+

(CH3)3 Cl-

18




obtained from computer simulations (dissipative particle dynamics)

chain leading to extended conformation Therefore the polymer molecule has a contracted coil

conformation at acidic pH and an extended conformation at basic pH as shown schematically in

Figure 25 In addition to pH-responsive behavior PAM is responsive to ionic concentration

(Klenina and Lebedeva 1983 Brondsted and Kopecek 1992 Samanta et al 2010) With

decreasing ionic strength the conformation varies from extended to coiled Note that the Flory-

Huggins parameter (χ) for PAM is 048plusmn001 in water at 30degC (Huang et al 2001)

23 Polyacrylamide-Montmorillonite Interactions and Associations

Polymers have been observed to adsorb onto clay mineral surfaces via van der Waals

forces electrostatic interactions and hydrogen bonding interactions (van Olphen 1977 Theng

1979) Polymer adsorption on a clay particle surface alters the surface properties of the particle

such as surface charge and hence interparticle forces Polymer characteristics at the solid-liquid

Contracted coiled

conformation at pH lt 4

Partially coiled

conformation at pH asymp 6

Extended conformation

at pH gt 105

Increasing extended conformation with increasing pH and with decreasing ionic strength

19

interface play an important role The interaction with clay particles can be complex due to

electrostatic forces chemical bonding and other forces operating simultaneously Understanding

the interplay and relative significance of each of these phenomena is critical to the interpretation

of a given polymerrsquos affect on a clay system

Polyacrylamide (PAM) has been observed to irreversibly adsorb onto clay mineral

surfaces and external surfaces of soil aggregates (Stutzmann and Siffert 1977 Gao and Heimann

1993 Lochhead and McConnell Boykin 2002) Interactions between clay particles and polymer

molecules result from (1) polymer bridging (2) charge neutralization or compensation (3)

complex formation between clay particle surfaces and polymer molecules or (4) a combination of

these mechanisms (Mortland and Brady 1970 van Olphen 1977 Pefferkorn et al 1987 Lee et

al 1991 Gao and Heimann 1993 Laird 1997 Dobias et al 1999 Mpofu et al 2003 Deng et

al 2006) Polymer bridging plays a major role in the presence of nonionic polymers (Theng

1982 Laird 1997 Hogg 1999 Deng et al 2006) while charge neutralization plays a major role

in the presence of cationic polymers

A nonionic polyacrylamide molecule strongly interacts with the clay surface via polymer

bridging reducing the overall negative charge through alteration of the electrical double layer

repulsive force (Fleer et al 1972 Carasso et al 1997 Besra et al 2002) A polymer molecule

can be adsorbed onto clay particles simultaneously bridging more than one particle The amide

group specifically the carbonyl oxygen (C=O) of PAM bonds to the edge site (Al-Al-OH or Al-

Mg-OH group) through hydrogen bonding Hydrogen bonding between the carbonyl group and

the face site is favored under acidic pH (Lochhead and McConnell Boykin 2002) Hydrogen

bonding also occurs between the oxygen atoms of clay and the protons of the amide group

(Haraguchi and Takehisa 2002) Hydrophobic bonding occurs between the hydrophobic

backbone (CH2-CH) of PAM and the hydrophobic basal face (ie uncharged sites on the siloxane

face) Exchangeable cations on the clay surface are bridged to the carbonyl oxygen of PAM

20

through ion-dipole interaction ie complex formation (Mortland and Brady 1970 Haraguchi and

Takehisa 2002 Ruiz-Hitzky and van Meerbeek 2006) Water molecules can bridge the

exchangeable cation together with the carbonyl oxygen through hydrogen bonding between the

water molecule and the carbonyl group and ion-dipole interaction between the water molecule

and the exchangeable cation

Polymer bridging can be modified by the molecular weight of the polymer the

conformation (ie coiled or extended) of polymer molecules and preexisting exchangeable

cations on the clay particle surface The conformation of PAM molecules in aqueous systems is

pH-dependent At pH = 6 both cationic and nonionic PAM molecules are neither fully extended

nor fully coiled that is intermediate conformation (Besra et al 2004) The importance of the

exchangeable cations in terms of ion-dipole interaction increases in the order Na+ K+ lt Ca2+

Mg2+ lt Al3+ lt Cu2+ Ni2+ (Deng et al 2006)

Coulombic attraction is the dominating bonding mechanism between the clay surface and

cationic PAM molecules (van Olphen 1977 Theng 1979 Laird 1997 Mpofu et al 2003) The

positively charged trimethyl ammonium groups (NR3) of cationic PAM are attracted to the

negatively charged sites along clay particle surface At the critical coagulation concentration

(CCC) of PAM all charges on the mineral surface are compensated Once the CCC is exceeded

aggregation occurs through van der Waals attraction The charged groups of cationic PAM may

also adsorb onto more than one particle and so may also contribute to polymer bridging

Cationic PAM molecules may also form an adsorption complex when a concentration of PAM

greater than the critical coagulation concentration is used The hydrophobic backbones (CH2-

CH) of the excess cationic PAM molecules link together through van der Waals attraction

Three different types of clay-polymer composites may be obtained when a clay particle is

associated with a polymer molecule in solution (Giannelis et al 1999 Alexandre and Dubois

2000 Ray and Okamoto 2003 Mai et al 2006 Ruiz-Hitzky and van Meerbeek 2006) (1)

21

phase-separated (microcomposite or conventional composite) (2) intercalated and (3) exfoliated

structures as shown in Figure 26 The phase-separated structure does not include polymer

intercalation into the interlayer space and thus interactions between a clay particle and a polymer

molecule lead to particle-level composites or microcomposites Properties of the phase-separated

composites are nearly the same as a traditional clay-polymer mixture Intercalated structure

develops when an extended polymer molecule is inserted between the particle layers The pattern

repeats every few nanometers maintaining a well-defined spatial relationship to each other ie

layered structure (Figure 26-b) Intercalation of clays by polymer is attributed to ion-exchange

reaction and ion-dipole interaction (Pospisil et al 2002 Pospisil et al 2004 Ruiz-Hitzky and

van Meerbeek 2006) Exchangeable cations in the interlayer space either replace with inorganic

andor organic cations or interact with polar neutral molecules intercalated between silicate

layers In an exfoliated structure which normally occurs with high polymer content the layers

are completely separated and the individual layers are distributed throughout the system

Exfoliation is identified by X-ray diffractograms with no diffraction peaks since the particle

layers have separated far from one another (gt 8 nm) Since the intercalated and exfoliated

structures result in layer-level composites or nanocomposites properties of the nanocomposites

may totally differ from the microcomposite This study focuses on the development and

manipulation of clay-polymer nanocomposites with intercalated structures

(a) (b) (c)


and (c) exfoliated structures

22

Polymer treatment alters the properties of Mt (van Olphen 1977 Theng 1979) For

example hydraulic conductivity of Mt increases with cationic polyacrylamide addition

(Ashmawy et al 2002) The mechanism of this phenomenon includes polymer bridging through

(1) the replacement of the adsorbed Na+ or Ca2+ in the clay by the cationic polymer molecules

(this process is likely to be irreversible since a number of cations on a single polymer chain

would need to be displaced simultaneously) and (2) a relatively weak dipole bond between the

cationic polymer molecule and Na+ In this case the replacement of Na+ is not likely since the

clay sheets are coated with the polymer

24 Synthesis of Clay-Polymer Nanocomposites

Clay-polymer nanocomposites (CPN) can be synthesized through four main techniques

(Gao and Heimann 1993 Vaia et al 1993 Yano et al 1993 Ray and Okamoto 2003 Gao

2004 Koo 2006 Mai et al 2006) (1) in-situ polymerization (2) solution exfoliation (3) melt

intercalation and (4) solution intercalation In-situ polymerization involves the construction of

polymer chains from monomers in solution within the clay particle interlayer space and

polymerization is initiated with heat radiation pre-intercalated initiators or catalysts (Zeng et al

2005) Extrapolating these extra steps to the macro-scale may inhibit the economic feasibility of

producing large quantities of intercalated materials especially when added heat or radiation is

required Solution exfoliation requires a solvent to exfoliate layered particles into single platelets

to which the polymers adsorb However this technique results in a polymer matrix ldquostuddedrdquo

with individual platelets In addition there are accompanying health and safety concerns due to

the organic solvent (Gao 2004) Melt intercalation requires heating the polymer matrix to a

molten state and then adding small quantities of clay material This process leads to a polymer

enhanced with clay rather than clay enhanced with a polymer

23

The intercalation of polymer molecules into clay particle interlayers without exfoliation

can be attained using solution intercalation (Yano et al 1993 Ray and Okamoto 2003 Gao

2004 Koo 2006 Mai et al 2006) which utilizes water-soluble polymers such as

polyacrylamide and swelling clay such as bentonite Intercalation by polymer molecules takes

place from a bulk polymer solution The interlayer water molecules are spontaneously displaced

with a polymer molecule due to negative variation in the Gibbs free energy (Theng 1979 Mai et

al 2006) The entropy obtained by desorption of water molecules from exchangeable cations in

the interlayer space compensates for the decrease in the overall entropy of the intercalated

polymer molecules leading to the polymer intercalation (Vaia et al 1993) Therefore the

reaction occurs without providing an external energy source implying better cost-efficiency than

other intercalation techniques In addition low health and safety risks can be expected due to the

use of water as a solvent

The solution intercalation technique has been successfully used to synthesize intercalated

structures of Mt with polymers such as poly(ethylene oxide) (Parfitt and Greenland 1970 Ruiz-

Hitzky and Aranda 1990 Wu and Lerner 1993 Shen et al 2002a) poly(acrylic acid) (Tran et

al 2005) polyacrylamide (Tanihara and Nakagawa 1975 Hwang and Dixon 2000) and

poly(vinyl alcohol) (Strawhecker and Manias 2000) Due to their linear structure poly(ethylene

oxide) molecules easily intercalate increasing the clay interlayer spacing to 223Aring (Parfitt and

Greenland 1970) The interlayer spacing of Mt mixed with poly(acrylic acid) or polyacrylamide

increases to 16Aring (Tran et al 2005) or to 155Aring (Hwang and Dixon 2000) respectively from

96Aring The interlayer spacing when treated with poly(acrylic acid) can be further increased to 20

Aring by increasing the mixing temperature up to 60˚C (Tran et al 2005) The interlayer spacing

tends to increase with increasing polymer concentration and mixing temperature and with

decreasing polymer molecular weight (Hwang and Dixon 2000 Shen et al 2002a Tran et al

2005) This study utilizes the solution intercalation technique for the aforementioned reasons

24

The solution intercalation technique has not attracted enormous interest because of its sensitivity

to experimental conditions such as polymer concentration (Shen et al 2002a) Thus it is

important to first understand the factors that control the extent of intercalation by the polymer in

order to develop a large-scale production technique

25 Characterization of Clay-Polymer Nanocomposites

251 X-ray Diffraction

Changes in the basal spacing of the synthesized clay-polymer composites is typically

characterized using X-ray diffraction (XRD) This is technique most often used to characterize

clay-polymer nanocomposites particularly with intercalated structures (van Olphen 1977 Koo

2006 Mai et al 2006) Intercalation of polymer molecules into the layer space increases the

interlayer spacing resulting in a shift of the diffraction peak towards lower angle values Thus

resulting interlayer spacing is calculated based on the Braggrsquos equation λ=2dmiddotsinθ where λ

denotes the wave length of the X-ray radiation (typically CuKa where λ=1541Aring ) d denotes the

interlayer spacing and θ denotes the measured diffraction angle

252 Spectroscopic Ellipsometry

Ellipsometry has previously been utilized to measure the thickness of the double layer

and adsorbed polymer layer on a surface (Lee and Fuller 1984 Irene 1993 Filippova 1998

Schwarz et al 1999 Russev et al 2000 Fan and Advincula 2002 Fan et al 2002 Wang et al

2004 Schmidt et al 2009) The technique detects the change in the polarization state of the light

modified by a sample surface Among the many techniques such as nuclear magnetic resonance

vibrational spectroscopy ellipsometry and neutron scattering that can be used to characterize

adsorbed polymer layers (Cohen Stuart et al 1986) ellipsometry illuminates in-situ

characteristics of adsorbed polymer molecules on a nearly flat surface such that effects of the

surface properties including roughness and curvature can be negligible Other benefits of using

25

ellipsometry are that the method is non-destructive non-invasive highly accurate requires only

small sample sizes and can be used on wet samples (Irene 1993 Russev et al 2000 Fan et al

2002) The achievable resolution can be lt 1 Aring but sensitivity to film thickness can be

maintained to tens of microns Changes in the polarization state result in different values of the

relative phase change Δ and the relative amplitude change which are characteristic angles of

the surface reflecting the polarized light perpendicularly (s-wave) and parallel (p-wave) to the

incidence plane The fundamental relationship between and is given as a complex reflection

coefficient (Irene 1993)

)exp()tan( i

||

||)tan(

s

p

r

r

sp

where p and s are the phase angles and rp and rs represent the complex amplitude reflection or

Fresnel coefficients The properties of the sample ndash optical properties in the form of the complex

refractive index (N = n +ik) or complex dielectric function (ε = ε1 + iε2 = N2) spectra and

microstructural factors such as film thickness ndash affect the measured spectra (Δ ψ) Thus the pH-

and time-dependent conformational changes of adsorbed polymer molecules onto a simulated

mineral surface may be captured through measurement of the spectroscopic ellipsometric angles

26 Computer Simulation

261 Overview

One important goal of simulation and modeling in material science is the accurate and

rapid prediction of materials and their properties and features Computer simulation may provide

a molecular level understanding of the mechanisms responsible for the behavior of clay-polymer

26

systems All forces and interactions occurring at a nano- andor micro-level can easily be

modeled by mathematical equations Such a technique not only complements experimental

results with a detailed atomistic level picture of the relevant phenomena but also illuminates

systems unaccessible via experimental methods Computer simulation and modeling of clays and

polymers based on theories and computational methods have long been used to study and

understand their complex behavior (Chang et al 1995 Skipper et al 1995 Boek et al 1996

Groot and Warren 1997 Sposito et al 1999 Balazs et al 2000 Bourg et al 2003 Cygan et al

2004b Pandey et al 2005 Sutton and Sposito 2006 Suter et al 2009) A number of

computational techniques have been used to investigate processes at different length and time

scales Figure 27 is a time-length scale plot illustrating current computational techniques at

relevant time and length scales

Quantum

Mechanics(electrons)

Mesoscale Simulation (molecules segments)

eg Coarse-grained MD DPD

Molecular

Mechanics(atoms)

Chara

cte

ristic

Length

Characteristic Time

mm

μm

nm

pico

seconds

nano

seconds

micro

seconds seconds minutes

FEM DEM

(finite elements)


and length scales Also shown are the basic interaction units in each method

27

Since atomistic simulation and modeling methods such as molecular dynamics (MD) and

Monte Carlo (MC) approach a realistic description of the system they are commonly used to

understand the behavior and properties of clays electrolytes and polymers (Skipper et al 1995

Sposito et al 1999 Chodanowski and Stoll 2001 Bourg et al 2003 Boulet et al 2004 Cygan

et al 2004b Laguecir and Stoll 2005 Katti et al 2006 Sutton and Sposito 2006 Ulrich et al

2006 Rotenberg et al 2007 Mazo et al 2008 Pagonabarraga et al 2010) However extreme

care must be taken in interpreting the results from such atomistic simulations since they can only

probe extremely small spatial dimensions and very limited time scales compared to experiments

In addition atomistic simulations take a significant amount of time and cost for predicting the

behavior of full-scale complex systems such as clay-polymer composites due to the restricted

length (~102 nm) and time scale (~102 ns) (Rotenberg et al 2007) For example a clay particle

with a width of 05μm and 100 layers would have about 01 billion atoms If such particles are

associated with a polymer molecule to form clay-polymer composites the system would

comprise too many atoms for atomistic simulation to equilibrate microscopic properties such as

radius of gyration or end-to-end distance

On the other hand the basic idea of coarse-grained atomistic computer simulation such

as coarse-grained molecular dynamics (CGMD) and dissipative particle dynamics (DPD) is to

decrease the system size These meso-scale computer simulations are based on spring-connected

particles so-called beads representing groups of atoms Thus the coarse-grained atomistic

technique has advantages in simulating and modeling large andor complex systems at a longer

timescale with current computer performance (Kremer and Grest 1990 Groot and Warren 1997

Goddard et al 2001 Muller-plathe 2002 Nieminen 2002 Kroger 2004 Boek et al 2005

Daivis et al 2007 Depa 2007 Fermeglia and Pricl 2007 Scocchi et al 2007 Zeng et al

2008 Luo and Sommer 2009 Suter et al 2009 Gruenert et al 2010) Figure 28 illustrates a

28

L AL

A

(a) (b)



Bond length (L) and bond angle (A) of the coarse-grained beads are also shown

schematic of coarse-graining a polymer chain and a clay particle where a monomer and a unit cell

of the clay particle respectively are replaced with a single bead

262 Dissipative Particle Dynamics

DPD was introduced by Hoogerbrugge and Koelman (1992) for addressing

hydrodynamic behavior of fluids While DPD is similar to molecular dynamics (MD) it has one

major difference in that a group of atoms a so-called coarse-grained bead is the basic unit of

DPD simulation Thus DPD has several advantages over the traditional MD technique For

example hydrodynamic behavior of a DPD system can be observed with fewer particles than that

required in an MD simulation which allows larger time steps to be taken than those in MD DPD

can simulate both Newtonian and non-Newtonian fluids including polymer solutions on

microscopic length and time scales

In the DPD approach all beads are defined by their mass mi position ir and momentum

ip Particles interact through a pairwise two-body short-ranged force ijF describing the sum

29

of a conservative force ijCF a dissipative force ij

DF and a random force ijRF (Espaňol and

Warren 1995 Groot and Warren 1997 Gibson et al 1998)

ijF = ijCF + ij

DF + ijRF

ijCF =

cij

cij

ij

ij

c

ij

ij

rrif

rrifr

r

r

ra

0

))(1(

ijDF = -γij∙ω

Dmiddotrijmiddotij

ij

ij

ij

ij

r

rv

r

r )(

ijRF = σijmiddot ω

Rmiddotrij

ij

ijij

r

r

t

where aij is the maximum repulsion between bead i and bead j rij = || ijr ijr = ji rr rc is the

cutoff radius γij and σij are the friction coefficient and noise amplitude between bead i and bead

j respectively ωD and ωR are r-dependent weight functions jjiiij mpmpv and ζij = ζji

is a Gaussian random number with zero mean and unit variance

It has been shown that the system obeys the fluctuation-dissipation theorem in which one

of the two weight functions fixes the other weight function if the following relationships hold

(Espaňol and Warren 1995)

ωD(r) = [ωR(r)]2

σ2 = 2γkBT

where kB is the Boltzmann constant and T is the temperature ωD(r) and ωR(r) are simply chosen

as (Groot and Warren 1997)

c

c

cRD

rrif

rrifr

r

rr

0

)1()]([)(

2

2

30

Neighboring beads in a polymer chain link together through a harmonic spring with the spring

constant ks and equilibrium bond length r0 (Groot and Warren 1997)

Fsij = ksmiddot(r ndash r0)

2

The spring constant for polymers ranges from 4 to 10 (Groot 2003 Qian et al 2007) The

equilibrium bond length ranging from 0 to 085rc has been adopted for a polymer molecule

(Gibson et al 1998 Gibson et al 1999 Rekvig et al 2003 Gonzalez-Melchor et al 2006)

This harmonic spring can also be used as a bond in a rigid particle For a rigid particle including

clay particles the spring constant varies from 50 to 100 (Rekvig et al 2003 Gonzalez-Melchor

et al 2006 Knauert et al 2007)

Electrostatic interactions play a key role in understanding the phenomena of a complex

system such as colloidal suspensions polymeric solutions and their mixtures Thus the

inclusion of electrostatic interactions in DPD simulations is essential to capture the micro-scale

phenomena including charged polymer adsorption on a clay particle clay intercalation by a

charged polymer and conformation of a charged polymer adsorbed on a surface Electrostatic

interactions in DPD simulations can be solved using a grid method modified Ewald sum method

or modified particle-particle particle-mesh (PPPM) technique (Groot 2003 Gonzalez-Melchor et

al 2006 Ibergay et al 2009) The grid method in which the electrostatic field is solved locally

on a grid efficiently captures the most important features of electrostatic interactions in a

reasonable manner Polyelectrolyte-surfactant systems were successfully simulated using this

method (Groot 2003) The modified Ewald sum method is a combination of the standard Ewald

method with some charge distribution on a particle that avoids the formation of nondesirable

ionic pairs due to soft repulsion of DPD beads The modified PPPM method in which charges

are distributed over a particle has also been successfully used to study charged polymer systems

(Ibergay et al 2009 Ibergay et al 2010) The standard Ewald method is known for accurately

describing Coulombic forces (Ewald 1921 Essmann et al 1995 Cygan et al 2004a Suter et

31

al 2007) However since computational efficiency is more important in a very complex system

the modified PPPM method was used in this study

DPD simulations usually operate in reduced units that are dimensionless Length mass

and energy are measured in units of a force cutoff radius the mass of a single DPD bead and kBT

where kB is Boltzmannrsquos constant and T is absolute temperature

32

Chapter 3

SYNTHESIS OF TUNABLE CLAY-POLYMER NANOCOMPOSITES

The purpose of the study described in this chapter is to develop an optimized procedure

for synthesizing clay-polymer nanocomposites using an expansive clay mineral (bentonite) and a

responsive polymer (polyacrylamide) for the future production of ldquotunablerdquo clay soils The

nanocomposites were produced using a solution intercalation technique that has potential for

large-scale production in situ Variables investigated include clay content polymer molecular

weight pH and clay-to-polymer volume ratio Changes in the basal spacing of bentonite were

characterized using X-ray diffraction

31 Introduction

In order to enhance engineering properties clay soils are often manipulated by physical

andor chemical processes including polymer addition However polymer treatment limits

further modification of the clay-polymer nanocomposites due to their irreversible interactions A

responsive polymer can be used to synthesize clay-polymer nanocomposites (CPN) the properties

of which vary with external environment triggers That is interlayer andor interparticle spacing

of the CPN can be manipulated through changes in the surrounding fluid pH ionic concentration

temperature or electric field For example CPN synthesized from a pH responsive polymer may

be further modifiable by exposing the CPN to alternate pH conditions Since the conformation of

pH-responsive polymers varies with pH the interlayer andor interparticle spacing may also vary

with pH By altering the fabric of the clay system at the particle level the meso-scale properties

such as void ratio permeability swelling potential and strength will also be affected For

example when the conformation of the polymer becomes coiled the interlayer andor

interparticle spacing decreases This leads to a dense fabric and a subsequent decrease in void

ratio Once the polymer is adsorbed in the interlayer space of swelling clays the swelling

33

behavior may also be controlled via the reversible conformational change of the responsive

polymer

In order to maximize the potential for interlayer and interparticle spacing modification

the optimized design of nanocomposites is CPN with intercalated structures in which polymer

molecules are adsorbed onto both the particle surface and interlayer surface Hence both

interparticle and interlayer spacing of the CPN are capable of further modification through

exposure to alternating pH conditions ie ldquotunablerdquo CPN

The purpose of this study is to develop an optimized procedure for synthesizing ldquotunablerdquo

CPN using an expansive clay mineral (montmorillonite) and a responsive polymer

(polyacrylamide) for the future production of in-situ modifiable clay soils Furthermore the CPN

should be created such that the potential for structure modification is maximized The CPN were

synthesized using a solution intercalation technique which has potential for in-situ large-scale

production The significance of this approach is that the optimized procedure found through this

study can be utilized to synthesize a new type of CPN which is tunable as well as feasible for in-

situ large-scale production The variables investigated in this study include clay content polymer

molecular weight pH and clay-to-polymer volume ratio Changes in the basal spacing of

montmorillonite were characterized using X-ray diffraction (XRD) Nuclear magnetic resonance

(NMR) spectroscopy was used to monitor mineral dissolution under the tested pH conditions

The effects of nanocomposite synthesizing temperature were also investigated

32 Experimental Study

321 Materials

3211 Bentonite

Montmorillonite (Mt) was chosen due to its large swelling capacity which provides the

greatest opportunity for polymer molecule adsorption onto both the particle surface as well as the

34

interlayer surfaces The clay mineral used in this study is an untreated Mt a dioctahedral

smectite with the chemical formula (NaCa)033(Al167Mg033)Si4O10(OH)2middotnH2O A sodium

bentonite from American Colloid Company (Arlington Illinois) designated commercially as

AEG powder was used as the sour of Mt The sodium bentonite comprises principally of Mt and

minor amounts of feldspar and quartz The chemical composition obtained from the supplier is

listed in Table 31 Selected properties of the clay material are given in Table 32 The Mt was

oven-dried for 24 hours at 105˚C prior to testing

3212 Polyacrylamide (PAM)

Polymer intercalation into the interlayer space of Mt was attempted using

polyacrylamides obtained from Cytec Industries Inc (West Paterson NJ) Polyacrylamide was

chosen because it is responsive to pH changes Specifically the conformation (expansion or

contraction) of a PAM molecule depends on the surrounding fluid pH The polymer molecule has

a contracted coil conformation at acidic pH and an extended conformation at basic pH (Michaels

1954 Al-Anazi and Sharma 2002 Besra et al 2004) as shown schematically in Figure 25

Therefore PAM molecules are expected to be more easily adsorbed onto the interlayer space at

basic pH leading to more intercalated structure formation than that at acidic pH PAM is also

sensitive to ionic concentration but this property was not considered in this study Hence ionic

concentration was kept constant The two types of polyacrylamides used in this study were high

molecular weight nonionic (NPAM) and low molecular weight nonionic (nPAM) These polymer

types were chosen to highlight the impacts of molecular weight difference on the formation of

intercalated structure Selected characteristics of the polymers are given in Table 33

35

Table 31 Chemical composition of the sodium bentonite used in this study (Supplier data)

component component

SiO2 6302

Al2O3 2108

Fe2O3 325

FeO 035

CaO 065

MgO 267

Na2O 257

trace 072

LOI 564

Table 32 Properties of the sodium bentonite used in this study

Property Values Methods

Median particle diameter D50 (μm) 272

Particle size distribution determined using a

Malvern Mastersizer S (Malvern Instruments

Ltd)

Specific gravity 25 Supplier data

Specific surface (m2g) 706 Modified methylene blue European spot

method (Santamarina et al 2002b)

pH (at solids content of 2) 85 Determined from pH measurement using the

Accumet XL50 pH meter (Fisher Scientific)

Isoelectric point (pH) 003

Determined from zeta potential

measurements using a PALS zeta potential

analyzer (Brookhaven Instruments Co)

Cationic exchange capacity

(cmolkg) 808

Ammonia-electrode method (Borden and

Giese 2001)

Table 33 Characteristics of polyacrylamides used in this study

Type Trade Name Structure (Barvenik 1994

Huang et al 2001) Molecular weight

(gmol) a

High molecular

weight N300

~ 6 x 106

Low molecular

weight N300LMW ~ 8 x 104

aMeasured using viscometry method (Brandrup and Immergut 1989 Ravve 2000)

n

CH

NH2

O = C

CH2

36

322 Synthesis of Clay-Polymer Nanocomposites ndash Solution Intercalation

The solution intercalation technique is a CPN synthesizing method in which clay

dispersions and polymer solutions are separately prepared and then mixed together Due to

negative variation in the Gibbs free energy polymer molecules are spontaneously intercalated

into the interlayer space of Mt (Theng 1979 Vaia et al 1993) Thus energy demand is minimal

implying cost efficiency and contributing to the capability of large-scale production for

geotechnical and geoenvironmental applications In addition in-situ production as well as low

health and safety risks can be expected due to the use of water as a solvent

Since Mt intercalation by a polymer molecule is affected by clay content (Shen et al

2002b Perez-Santano et al 2005) polymer concentration (Hwang and Dixon 2000 Shen et al

2002a) polymer molecular weight (Hwang and Dixon 2000 Heinz et al 2007) and pH (Besra

et al 2004 Perez-Santano et al 2005) selected variables investigated in this study using the

solution intercalation technique include clay content polymer molecular weight pH and clay-to-

polymer volume ratio The clay content is defined as the proportion of clay volume with respect

to the total dispersion volume Dispersions were prepared at clay contents of 0001 0005 001

and 003 representing a broad range of clay content in geotechnical and environmental

applications The high molecular weight polymer has MW ~ 6x106 gmol and MW of the low

molecular weight polymer is ~ 8x104 gmol The polymer solution pH was modified to target

acidic (pH asymp 4) neutral (pH asymp 6) and basic (pH asymp 11) conditions The polymer molecule

conformational change results from hydrolysis and reaction on the amino functional group

(Barvenik 1994 Kurenkov 1997 Bruice 2001) Hydrolysis and the amino group reactions

occur very slowly at pH below 9 and below 45 respectively Since the conformational change is

insignificant at pH below 45 the acidic target pH used was pH 4

The clay-to-polymer volume ratio is defined as the proportion of clay volume with

respect to polymer volume and is used to consider both clay content and polymer concentration

37

simultaneously An example calculation for clay-to-polymer volume ratio can be found in

Appendix A A broad range of clay-to-polymer volume ratios were considered in this study

125 2 4 8 125 25 and 625

Clay dispersions were prepared at the specified clay contents by mixing the appropriate

mass of oven-dried clay in deionized water The dispersion was placed on a magnetic stirrer and

stirred for 24 hours to provide enough separation of interlayers ie swelling This step is herein

referred to as the swelling stage

Polymer solutions were prepared according to the designated clay-to-polymer volume

ratio by mixing the appropriate mass of each polymer in deionized water The solution was

stirred for 24 hours The pH of the solution was adjusted to the target pH by using 01M HCl or

01M NaOH buffer solutions After adjusting the pH the polymer solution was mixed thoroughly

with the prepared clay dispersion for 24 hours This step is herein referred to as the mixing stage

During mixing the dispersion was covered to prevent evaporation The mixture of clay and

polymer was then air-dried and pulverized using a pestle and mortar The solution intercalation

process was performed a total of three times per test condition

323 Mixing and Drying Temperatures

Mixing temperature has been reported as a factor affecting changes in basal spacing of

Mt treated with a polymer (Tran et al 2005 Filippi et al 2007) The basal spacing of Mt treated

with poly(acrylic acid) was further expanded at a mixing temperature of 60˚C compared to room

temperature (Tran et al 2005) However analogous information is not available for Mt treated

with polyacrylamide In addition determining the optimum composite synthesis conditions is the

first step in designing future feasibility studies for large-scale production especially in terms of

additional energy consumption In order to investigate the effect of mixing temperature samples

were prepared at clay content of 002 pH 11 and clay-to-polymer volume ratio of 8 These

synthesis conditions were randomly chosen within the boundaries for intercalated structure

38

formation ie clay content lt 003 and clay-to-polymer volume ratio lt 25 The samples were

mixed at room temperature (21 plusmn 2˚C) 60˚C and 85˚C and then air-dried Samples to

investigate the effect of drying temperature (post mixing stage) were prepared at clay content of

001 pH 11 and clay-to-polymer volume ratio of 125 These synthesis conditions were

randomly chosen as above The samples were then dried at 110˚C and room temperature and

then ground into powder form

324 Analysis Techniques

3241 X-ray Diffraction (XRD)

Changes in the basal spacing of the synthesized clay-polymer composites were

characterized using X-ray diffraction (XRD) This technique is most often used to characterize

clay-polymer composites particularly intercalated structures (van Olphen 1977 Koo 2006 Mai

et al 2006) Intercalation of polymer molecules into the clay particle increases the interlayer

spacing resulting in a shift of the diffraction peak towards lower diffraction angle values (2θ lt

7˚)

The pulverized clay-polymer composites ie powder form (approximately 05 g by

weight) were placed in a zero-background holder consisting of a quartz crystal cut polished 6deg of

the c-axis The holder filled with the sample was introduced to the XRD instrument XRD

spectrums for the treated samples were obtained with a Scintag Pad V (Scintag Inc Cupertino

CA) operated at 35 kV voltage and 30 mA current with Cu Kα radiation (λ = 154178 Aring )

Quantitatively analyzing XRD results of clay samples is theoretically possible using Rietveld

XRD quantification (Rietveld 1967 Ufer et al 2008) However quantification of XRD results

for clay-polymer nanocomposites presents its own challenge since particles may not be aligned

and no database on clay-polymer complexes exists In addition the XRD peaks from this study

are low-angle (2θ lt 10˚) This diffraction angle range is not ideal for obtaining reliable

39

diffraction signatures due to distorted reflections (Moore and Reynolds 1997) Therefore for the

purpose of this study it is assumed that particles are oriented in the same direction and the

relative degree of intercalation is compared using XRD intensity data Note that the XRD peak

position for each diffractogram was determined using Jade 9+ software (Materials Data Inc

Livermore CA)

3242 Nuclear Magnetic Resonance (NMR) Spectroscopy

The effects of mineral dissolution at pH 4 and pH 11 were investigated using nuclear

magnetic resonance (NMR) spectroscopy coupled with X-ray diffraction (XRD) NMR spectra

are used to identify the structural and dynamic properties of solids including clay minerals and

clay-based materials (Sanz and Serratosa 2002) NMR spectra provide information on whether

or not layer distortions have occurred XRD patterns provide information on whether or not the

layered structure of the tested clay minerals remains intact Thus XRD patterns as well as solid-

state 29Si 27Al MAS NMR spectra can be used as indicators of the final structure of CPN

High-resolution 29Si 27Al MAS NMR spectra of the sample (approximately 02 g by

weight) in powder form were recorded using a Bruker Avance 300 spectrometer and 5 mm Doty

MAS probes spun at 6 kHz for Si and 15 kHz for Al respectively A 1 μs (π10) pulse with 30 s

delay was used for 29Si and a 1 μs (π10) pulse with 1 s delay was used for 27Al

33 Results and Discussion

The characteristic basal spacings obtained using XRD for the synthesized

nanocomposites are summarized in Table 34 and plotted in Figures 31 and 32 Sample

numbers in Table 34 beginning with CC MW PH and CP indicate the corresponding variables

clay content polymer molecular weight pH and clay-to-polymer volume ratio respectively

Sample numbers beginning with N represent a clay sample without polymer treatment XRD

intensity represented as counts indicates the relative amount of a structure with a particular basal

40

Table 34 Test matrix and resulting basal spacing with XRD intensity

Sample

numbera

Clay

content

Polymer

type

pH of

polymer

solution

Clay-to-

polymer

volume ratio

Basal spacing

(nm)b

XRD intensity

at peak

(counts)

N1 0001 na na na

1227 150

N2 001 1166 160

CC1 0001 nPAM 109 8 1526 225

CC4 0005 nPAM 109 8 1509 280

CC7 001 nPAM 1094 8 1515 200

CC10 003 nPAM 111 8 1215 210

MW1 001 nPAM 1094 125 1527 1211 180 180

MW4 001 NPAM 1096 125 1558 1151 130 115

PH1 001 nPAM 41 8 1515 1289 230 180

PH4 001 nPAM 565 8 1515 1308 210 175

PH7 001 nPAM 1094 8 1515 200

CP1 0001 nPAM 109 125 1557 310

CP4 0001 nPAM 11 2 1541 460

CP7 0001 nPAM 1104 4 1504 400

CP10 001 nPAM 111 8 1515 1289 230 180

CP13 001 nPAM 1094 125 1527 1211 180 180

CP16 001 nPAM 109 25 1108 310

CP19 001 nPAM 1092 625 1164 225 a For clarity iterations under each condition are not tabulated but still found in text or in plots

b All XRD peaks within 2θ below eight degrees (basal spacing greater than approximately 11nm) are

tabulated

spacing (Moore and Reynolds 1997) Thus the intensity corresponding to basal spacings greater

than 145Aring is directly related to the quantity of intercalated structures Results of the mineral

dissolution study are shown in Figures 33 and 34

331 Influence of Mixing and Drying Temperatures

Mixing temperature appeared to have no impact on the formation of intercalated structure when

using the low molecular weight polyacrylamide over the range of temperatures tested (Figure

31) Note that basal spacings larger than 145Aring indicate the formation of intercalated structure

since the height of the PAM monomer is approximately 51Aring (Bruice 2001) For

nanocomposites formed with nPAM (Figure 32-a) and nanocomposites formed with NPAM

41

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1479nm1278nm

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1495nm1192nm

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1494nm1253nm


60degC and (c) 85degC mixing temperatures

(Figure 32-b) drying temperature did not significantly influence intercalation Furthermore the

difference between the second basal spacings (room-temperature vs oven-temperature) was

approximately the size of a water molecule (approximately 2 ~ 34Aring ndash Skipper et al 1995) This

observation was confirmed by comparing these results (Figure 32) with samples of hydrated

clay N1 and N2 (Table 34) which were prepared following the same synthesizing procedures

except without polymer addition The comparison of basal spacings at different drying

(a)

(b)

(c)

42

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1527nm1211nm

21plusmn2˚C

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1509nm

1005nm

110˚C

(a)

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1558nm1151nm

21plusmn2˚C

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1511nm

1005nm

110˚C

(b)


drying temperatures with (a) low molecular weight PAM and (b) high molecular weight PAM

43

temperatures indicated that the drying temperature did not influence the intercalation and

confirmed that the clay particle was intercalated by the polymer molecule Thus all remaining

attempts at forming nanocomposites were completed at room temperature for both the mixing and

drying stages

332 Mineral Dissolution

NMR and XRD results to investigate the impact of pH on mineral dissolution are shown

in Figures 33 and 34 Figure 33 presents typical NMR characteristics of Mt Tetrahedral

silicon corresponds to -935 ppm on the Si-NMR spectra and tetrahedral and octahedral

aluminum peak at 58737 and 3917 ppm respectively on the Al-NMR spectra (Kinsey et al

1985) The lack of shifting in the NMR peak positions for nanocomposites synthesized with pH-

adjusted (Figure 33-b and 33-c) and unadjusted (Figure 33-a) polymer solutions indicated that

the acid or base added during the polymer solution pH-adjustment step did not impact mineral

dissolution when the polymer solution was mixed with the clay dispersion This result was

confirmed in the XRD diffractogram which showed that the typical characteristics of Mt

remained for nanocomposites synthesized with pH-adjusted and unadjusted polymer solutions

(Figure 34) Figures 33 and 34 indicate that the amount of mineral dissolution of the CPN due

to exposure to the pH-adjusted solutions (pH asymp 4 and pH asymp 11) did not differ significantly from a

nanocomposite synthesized with unadjusted polymer solution Figure 34 also indicates that

PAM treatment increased the interlayer spacing due to the formation of intercalated structure

44




adjusted polymer solutions (e) pHasymp4 and (f) pHasymp11

(c)

(b)

(a)

(f)

(e)

(d)

-935

-1062

3917

58737

45

2 7 12 17 22 27

Rel

ativ

e In

ten

sity

2θ˚ (CuKα)

15 nm



denotes a typical peak for Mt

333 Nanocomposite Synthesis Optimization


nanocomposites are summarized in Table 34 and plotted in Figures 35 and 36 as a function of

the variables considered in this study

(a)

(b)

(c)

M M

M M

M M

46

0

100

200

300

400

500

0001 001 01

Inte

nsi

ty (

cou

nts

)

Clay content



bars were plotted based on the calculated standard deviation of three measured values

The relationship between clay content and XRD intensity for intercalated structure is

plotted in Figure 35 The clay content was defined as the proportion of clay volume with respect

to the total dispersion volume With respect to clay content intercalated structure occurred at

clay contents of 0001 0005 and 001 but not at clay content of 003 As clay content increased

less intercalated CPN formed Polymer molecules tend to be adsorbed first onto particle surface

due primarily to accessibility thus more clay particles may hinder the interlayer adsorption of

polymer At clay content of 003 no intercalated structure formation implies that the polymer

adsorption takes place on the particle surface first

Intercalated structure occurred in the presence of both low molecular weight PAM and

high molecular weight PAM However the difference in molecular weight led to slight

differences in basal spacing and amount of intercalated structure (Table 34) When all other

nanocomposite synthesis conditions were held constant the low molecular weight PAM

nanocomposites resulted in a higher XRD intensity than the nanocomposite synthesized with high

47

molecular weight PAM The slightly lower quantity of intercalated structures with high

molecular weight PAM is consistent with its larger size This observation is similar to that of

other researchers in that smaller molecules penetrate more easily into interlayer spaces (Aranda

and Ruiz-Hitzky 1992 Hwang and Dixon 2000 Inyang and Bae 2005)

The effect of polymer conformation was insignificant XRD intensity and basal spacing

at all tested pH ranges were nearly constant The polyacrylamide used in this study has extended

conformation at basic pH while it has contracted coil conformation at acidic pH (Figure 25)

Thus PAM molecules were expected to be more easily adsorbed onto the interlayer space at basic

pH leading to more intercalated structure formation than that at acidic pH However the results

indicate that the polymer solution pH did not significantly influence the formation of intercalated

structure One possible reason for this observation is due to pH neutralization during mixing with

clay dispersion Since pH adjustment was performed for the polymer solution only it is very

likely that adjusted pH of polymer solution was neutralized when added to the clay dispersion

(pH not adjusted) diminishing the effect of polymer conformation This was confirmed with pH

values measured after mixing that ranged from pH 75 to pH 9

The formation of intercalated structure tends to increase with decreasing clay-to-polymer

volume ratio (Figure 36) The quantity of intercalated structures was maximized at a clay-to-

polymer volume ratio of 2 Beyond this apparent maximum XRD intensity decreased with

decreasing clay-to-polymer volume ratio At the lowest tested clay-to-polymer volume ratio of

125 the reduction in intensity suggests exfoliation of the clay particles (Wang and Pinnavaia

1994 Alexandre and Dubois 2000 Biswas and Ray 2001) As exfoliated structures form the

XRD intensity corresponding to the quantity of intercalated structures decreases On the other

hand the lowest quantity of intercalated structures corresponded to the clay-to-polymer volume

ratio of 125 These results indicate that the formation of intercalated structure in part is

determined by the applied clay-to-polymer volume ratio

48

0

100

200

300

400

500

1 10 100

Inte

nsi

ty (

coun

ts)

Clay-to-Polymer Volume Ratio




335 Dominant Factor for Intercalated Structure Formation

Most of the conditions tested here exhibited expanded basal spacing (greater than 145Aring )

which is an indication of the formation of intercalated structure However intercalated structure

indicated by basal spacing gt145Aring was not observed in samples CC10 CP16 and CP19 CC10

sample was synthesized at clay content 003 while CP16 and CP19 were synthesized at clay-to-

polymer volume ratios of 25 and 625 (Table 34) While clay content polymer molecular

weight and clay-to-polymer volume ratio affect the formation of intercalated structure based on

the increase in XRD intensity clay content and clay-to-polymer volume ratio are the most

significant factors tested here Polymer molecular weight and polymer solution pH (in the tested

range) play a less critical role The most significant factor affecting intercalated structure

formation was the clay-to-polymer volume ratio From samples CP16 and CP19 although clay

49

content was expected to form intercalated structures the measured basal spacings did not exceed

145Aring due to the high clay-to-polymer volume ratio (gt 125)

34 Conclusions

The purpose of this study is to develop an optimized procedure for synthesizing clay-

polymer nanocomposites (CPN) using an expansive clay and a pH-responsive polymer for the

goal of creating ldquotunablerdquo nanocomposites Factors such as clay content polymer molecular

weight pH and clay-to-polymer volume ratio that influence the formation of intercalated

structure were investigated The solution intercalation technique was found to be appropriate for

synthesizing CPN using bentonite and polyacrylamide a responsive polymer

When synthesizing CPN the mixing and drying temperatures do not appear to affect the

formation of intercalated structure for nanocomposites of bentonite and polyacrylamide

Synthesizing these nanocomposites at high temperatures provides no advantage over synthesizing

at room temperature In the tested temperature range the solution intercalation technique is

promising for synthesizing bentonite-polyacrylamide nanocomposites with no additional energy

consumption

Nuclear magnetic resonance spectra and X-ray diffraction indicate that the mineral

dissolution due to pH-adjusted polymer solutions is insignificant It is likely that mixing the pH-

adjusted polymer solution with the clay dispersion (not pH-adjusted) results in pH neutralization

Such pH neutralization also affects conformational behavior of polyacrylamide molecules

minimizing the pH effect on the synthesis of intercalated structure

The formation of intercalated structure is maximized by the appropriate clay content

polymer molecular weight and clay-to-polymer volume ratios Intercalation was successful at

clay content below 003 and clay-to-polymer volume ratio below 25 While clay content

polymer molecular weight and clay-to-polymer volume ratio affect the formation of intercalated

50

structure the most significant factor is the clay-to-polymer volume ratio The formation of

intercalated structure is expected only when appropriate clay-to-polymer volume ratio of less than

25 is applied At clay-to-polymer volume ratios below 25 intercalated structure formation

increases with decreasing clay content and polymer molecular weight The quantity of

intercalated material tends to increase with decreasing clay-to-polymer volume ratio and has an

apparent maximum at the ratio of 2 Using low molecular weight polyacrylamide was slightly

more efficient in forming CPN compared to high molecular weight polyacrylamide The smaller

size of the low molecular weight polyacrylamide molecule allows for easier insertion into the

interlayer space of the particle

51

Chapter 4

MANUPULATION OF SYNTHESIZED CLAY-POLYMER

NANOCOMPOSITES

The purpose of this chapter is to investigate the responsiveness or tunability of clay-

polymer composite materials with controllable micro-scale properties such as interlayer and

interparticle spacing and with controllable meso-scale properties including specific surface area

swelling potential and permeability Descriptions of experimental methods and their

interpretation are provided verifying that the micro-scale conformational changes of polymer lead

to meso-scale property changes

41 Introduction

Soils are often modified with the use of polymers or surfactants in the fields of material

science geotechnical and geoenvironmental engineering (Gardner and Arias 2000 Bhardwaj et

al 2007 Story et al 2009 Young et al 2009) Polymer additions alter soil fabric enhancing

engineering properties such as swelling behavior (Hjelmstad 1990 Inyang et al 2007) water

permeability (Young et al 2009) contaminant barrier properties (Inyang and Bae 2005) water

retention (Bhardwaj et al 2007) and material properties such as thermal resistance toughness

and water permeability (Strawhecker and Manias 2006) The use of responsive polymers has an

additional benefit of controllable morphologies Morphologies of pH- ionic strength-

temperature- and electrical potential-responsive polymers are tunable with each environmental

trigger inducing controllable system properties (Bae et al 1990 Feil et al 1992 Wu and Shanks

2003 Kim et al 2006 Xia et al 2006)

Many studies have focused on the investigation of conformation of polymers adsorbed on

a clay mineral surface using ellipsometry nuclear magnetic resonance scanning probe

52

microscopy diffuse reflectance Fourier transform infrared spectroscopy and Monte Carlo

simulation (Bottero et al 1988 Takahashi 1991 Chodanowski and Stoll 2001 Brotherson et

al 2007 Blachier et al 2009) Only a few studies have attempted to characterize polymer

conformation adsorbed in the interlayer space of a clay mineral (Glinel et al 2001) However

conformational behavior of a responsive polymer after adsorption has not been studied since

current experimental technologies limit the ability to characterize the conformation of the

polymer adsorbed on a mobile suspended surface ie clay particle in water Understanding the

conformational behavior of a responsive polymer adsorbed on a surface is critical to predicting

the behavior of tunable CPN

This study utilizes a pH-responsive polymer since the high solubility of a pH-responsive

polymer is advantageous for large-scale production necessary for in-situ engineering applications

pH-responsive polymers may have various conformations as a function of the surrounding fluid

chemistry which could lead to changes in CPN properties Therefore the objective of this

chapter is to link micro-scale conformational behavior of a pH-responsive polymer to meso-scale

properties of CPN Micro-scale tests such as dynamic light scattering and spectroscopic

ellipsometry were used to investigate micro-scale conformational behavior of the pH-responsive

polymer The polymer conformation in a bulk aqueous solution was investigated using dynamic

light scattering Spectroscopic ellipsometry was used to explore the polymer conformation on a

surface Meso-scale tests including specific surface area measurement swelling potential

measurement and hydraulic conductivity tests were conducted to explore meso-scale properties

of CPN corresponding to micro-scale polymer conformations A linkage between the micro-scale

polymer conformation and the meso-scale properties of CPN will be made For example CPN

synthesized using polyacrylamide is expected to have greater interlayer and interparticle spacings

ie open fabric at pH above 11 than that at pH below 10 Thus the swelling potential of the

CPN would be maximized at pH above 11 resulting in minimal permeability

53

42 Materials

421 Clay Minerals



interlayer surfaces The clay mineral used in this study was an untreated Mt a dioctahedral

smectite with the chemical formula (NaCa)033(Al167Mg033)Si4O10(OH)2middotnH2O The source of Mt

is a sodium bentonite from American Colloid Company (Arlington Illinois) designated

commercially as AEG powder This bentonite comprises principally of Mt and minor amounts of

feldspar and quartz The chemical composition obtained from the supplier is listed in Table 41

Selected properties of the clay material are given in Table 42 The Mt was oven-dried for 24

hours at 105˚C prior to testing

Kaolinite was also used to investigate effects of interlayer spacing modification

Kaolinite has little swelling potential and cannot easily be intercalated by a polymer while Mt

has a high swelling potential and is easily intercalated by a polymer providing the ability for

interlayer spacing modification Thus only interparticle spacing can be modified in the case of

kaolinite treated with polymer The kaolinite used in this study was an untreated kaolin from

Wilkinson Kaolin Associates LLC (Gordon Georgia) The kaolinite designated commercially as

Wilklay SA-1 is a dioctahedral kaolinite with the chemical formula Al2O3middot2SiO2middot2H2O The

chemical composition is nearly the same as theoretical kaolinite indicating a high level of purity

(Table 41) The kaolinite was converted to a monoionic sodium kaolin using a conversion

method modified after van Olphen (1977) and Palomino and Santamarina (2005) The method

consists of mixing the kaolin in a 2M NaCl solution for 48 hours and a 1M NaCl solution twice

for 24 hours each time After the final salt wash the excess salt is removed by replacing the

supernatant fluid with deionized water until the supernatant conductivity measures less than 100

microScm The converted clay slurry is oven-dried and ground using a pestle and mortar The

54

kaolinite contains small content of illite impurity confirmed by X-ray diffraction (Kim and

Palomino 2009)

Table 41 Chemical composition of clay minerals used in this study

constituent

constituent

Kaolinite

(Supplier Data)

Theoretical kaolinite

(Murray 1991)

Bentonite

(Supplier Data)

SiO2 456 463 6302

Al2O3 384 398 2108

Fe2O3 04 325

FeO 035

TiO2 15

CaO 006 065

MgO trace 267

K2O 018

Na2O trace 257

trace 072

LOI 1382 139 564

Table 42 Properties of clay materials used in this study

Property Kaolinite Bentonite

Median particle diameter D50 (μm) 168a 272b

Specific gravityc 26 25

Specific surfaced (m2g) 4037 70646

pH (at solids content of 2)e 75 85

Isoelectric point (pH)f 23 003

Cationic exchange capacity (cmolkg)g 23 808 a Hydrometer test (ASTM 2003) b Particle size distribution determined using a Malvern Mastersizer S (Malvern Instruments Ltd)

c Supplier data

d Modified methylene blue European spot method (Santamarina et al 2002b) e Determined from pH measurement using the Accumet XL50 pH meter (Fisher Scientific)

f Determined from zeta potential measurements using a PALS zeta potential analyzer (Brookhaven

Instruments Co) g Ammonia-electrode method (Borden and Giese 2001)

55

422 Polyacrylamide

Polyacrylamide (PAM) was chosen because it is responsive to changes in pH

Specifically the conformation (expansion or contraction) of a PAM molecule depends on the

surrounding fluid pH The polymer molecule has a contracted coil conformation at acidic pH and

an extended conformation at basic pH (Michaels 1954 Al-Anazi and Sharma 2002 Besra et al

2004) as shown schematically in Figure 25 PAM is also sensitive to ionic concentration but

this property was not considered in this study Hence ionic concentration was kept constant

For most of the tests the clay minerals were treated with low molecular weight nonionic

PAM (nPAM) In the hydraulic conductivity testing (Section 443) high molecular weight

nonionic PAM (NPAM) and high molecular weight cationic PAM (CPAM) containing 20

cationic quaternary ammonium salt groups were also used to highlight the impacts of polymer

molecular weight and ionic type respectively All three types of PAM were obtained from Cytec

Industries Inc West Paterson NJ Selected characteristics of the polymers are given in Table 43


Type Trade Name Structure (Barvenik 1994 Huang

et al 2001) Fraction of

charged units

Molecular

weight (gmol) a

NPAM N300

None ~ 6 x 106

nPAM N300LMW None ~ 8 x 104

CPAM C494

20)(

ba

b ~ 4 x 106

a Measured using viscometry method (Brandrup and Immergut 1989 Ravve 2000)

a

CH

NH2

O = C

CH2

a

CH

NH2

O = C

CH2 CH2

b

CH

N+

O = C

O

(CH2)2

(CH3)3

Cl-

56

Degree of hydrolysis τ = b (a+b) was determined by acid-base titration (Anthony et al 1975)

τ = 1 defines the chemical formula of poly(acrylic acid) The degree of hydrolysis employed in

this study is a statistical quantity thus it does not correlate with the conformation of the polymer

molecule (Michaels 1954)

423 Synthesis of CPN and Microcomposites

Clay-polymer nanocomposites were synthesized through a solution intercalation

technique using bentonite and PAM The clay content and clay-to-polymer volume ratio were

0001 and 2 respectively which were the optimum conditions for the greatest quantity of

intercalated structure (Kim and Palomino 2011) Figure 41 shows scanning electron microscopy

images for bentonite and the synthesized CPN The synthesized CPN was (1) used in gel-form

or (2) air-dried and ground using pestle and mortar ie powder-form Gel-form CPN is the

synthesized CPN prior to air-drying and grinding

Kaolinite-PAM microcomposites were synthesized by mixing kaolinite slurry with PAM

solution for 24 hours The microcomposites were used to highlight affects of interlayer spacing

modification when compared to montmorillonite-PAM composites The concentration of PAM

was 240 mgL ie clay-to-polymer volume ratio = 625 which was the optimum condition for

the formation of microcomposites (Kim and Palomino 2009) Figure 42 shows scanning

electron microscopy images for kaolinite and the synthesized microcomposite Two types of

composites gel-form and powder-form were prepared as above

57

(a) (b)


using bentonite and PAM

(a) (b)


synthesized using kaolinite and PAM

43 Micro-Scale Characterization

The term ldquomicrordquo used in this study is defined as the level of a clay particle ie lt 2 μm

in length Responsiveness of PAM in terms of conformation was investigated using dynamic

light scattering (DLS) and spectroscopic ellipsometry (SE) Although the polymer is expected to

have a particular conformation in a dilute solution it is not guaranteed that the polymer will have

3 μm 25 μm

5 μm 10 μm

58

the same conformation when adsorbed onto a clay mineral surface since the properties of a

surface play a critical role in the conformational behavior (Michaels 1954 Fleer 1993) Thus it

is important to characterize conformational behavior of the polymer not only in a dilute solution

but also on a clay mineral surface The polymer conformation in a dilute solution was

investigated using DLS while SE was used to explore conformational behavior of the polymer

adsorbed on a clay mineral surface

431 Dynamic Light Scattering

In a dilute solution where a conventional viscometer does not have enough sensitivity

dynamic light scattering (DLS) has been proven to be a powerful method to study the

morphology of clay particles polymer molecules and their complexes (Berne and Pecora 1976

Francois et al 1979 Kulicke et al 1982 Muzny et al 1996 Pignon et al 1996 Peng and Wu

1999 Nelson and Cosgrove 2004 Wu et al 2006 Connal et al 2008) Dynamic light

scattering offers many advantages speed versatility small sample size and measurement time

independent of particle density It is also a non-destructive technique For sub-micron sizes it is

sometimes the only viable technique

If a laser beam falls on a polymer solution and impinges upon the molecular particles the

electrons of the particles are induced to vibrate such that they interfere with the transmission of

light and cause scattering in various directions The fluctuations in the scattered light which are

related to the motion of the particles are measured For a dilute monodispersed suspension of

noninteracting particles the relaxation of the fluctuations (Г) is described by

Dn 2

0

))2

sin(4

(

where n is the refractive index of the suspending liquid λ0 is the wavelength of the laser in

vacuum α is the scattering angle and D is the particle diffusion coefficient For spherical

59

particles the Stokes-Einstein relationship relates the particle diameter d and the diffusion

constant D

Dt

Tkd B

)(3

where kB is the Boltzmannrsquos constant T is the absolute temperature and η(t) is the viscosity of

the liquid in which the particle is moving

A Mt dispersion and an nPAM solution were prepared at clay content of 4x10-5 and

polymer concentration of 15 mgL respectively The samples were then treated with 01M HCl

and NaOH solutions to reach the target pH (pH 3 6 and 115) DLS was performed using a nano

zeta potential and submicron particle size analyzer Beckman Coulter Delsa 400SX (Brookhaven

Instruments Corporation Holtsville NY) The wavelength of the laser light is 635nm

Measurements were conducted at 25 degC and the scattering angle was set at 90deg DLS was carried

out a total of two times per test condition PAM molecules were expected to have pH-dependent

hydrodynamic radius since PAM expands with increasing pH

10

100

1000

1 3 5 7 9 11 13

Hy

dro

dy

nam

ic R

adiu

s (

nm

)

pH

Mt

nPAM

Figure 43 Hydrodynamic radius of montmorillonite and nPAM as a function of pH

60

Figure 43 shows DLS results for montmorillonite and nPAM as a function of pH The

molecule size of nPAM was affected by pH as expected The hydrodynamic radius increased

with increasing pH The hydrodynamic radius of the polymer at pH 115 is approximately five

times larger than that at pH 3 Since the hydrolysis rate of PAM is theoretically the same at pH

below pH 10 the hydrodynamic radius at pH 6 was expected to be nearly the same as that at pH 3

However it was experimentally found that PAM molecules have slight negative charges even at

neutral pH due to hydrolysis of the amide group into acrylic acid (Kurenkov 1997) Repulsion

forces between negatively charged groups of PAM molecules induced expanded coiled

conformation at pH 6 With increasing pH the expanded coiled nPAM molecules become

extended (pH 115) The hydrodynamic radius of Mt in the dispersion also appeared to be pH-

dependent Since Mt has pH-dependent charges on its surface (Schindler 1981 Mohan and

Fogler 1997) flocculationaggregation the degree and extent of which are a function of pH

occurs leading to pH-dependent particle size

DLS results confirm that PAM is pH-responsive in an aqueous solution However DLS

cannot capture the conformation of PAM in the interlayer space of CPN since DLS does not

provide information on the location of polymer molecules Even if PAM in CPN is still pH-

responsive the pH-dependent behavior of Mt may hinder DLS from characterizing PAM

conformation of CPN


In order to investigate the pH-responsiveness of PAM in CPN it has to first be

demonstrated that PAM is still pH-responsive on a surface In this chapter PAM molecules were

adsorbed onto a fixed surface simulating a clay mineral surface After the polymer adsorption

pH-responsiveness of PAM was explored at various pH values using SE The conformational

61

behavior of PAM adsorbed on the simulated surface is expected to be a function of ambient

solution pH

Amorphous SiO2 was used to simulate a clay mineral surface A simulated surface was

used instead of a real clay particle in order to accurately capture adsorbed PAM conformation and

its evolution using SE The complexities associated with utilizing true clay particles in

suspension (mobile suspended surface) with the technique would yield results that are difficult to

interpret Thus a simpler system was devised that would isolate the behavior of interest The

amorphous SiO2 layer used is simply the native oxide of crystalline silicon (c-Si) wafer The

simulated surface was placed at the bottom of a fused silica vessel with windows at 20deg to the

sample surface normal such that the incident light from the ellipsometer passes through the

windows at normal incidence as schematically shown in Figure 44 A polymer solution (1875

mgL) of 150ml was introduced to the vessel the polymer was allowed to adsorb onto the

simulated surface for 2 hours Since it has been reported that the adsorbed amount of PAM on a

silica surface reaches equilibrium within about an hour (Stemme et al 1999) a 2-hour time

period was selected to allow for PAM to be uniformly adsorbed onto the simulated surface

Consequently the adsorption density was same throughout the surface Also the equilibrium

period did not affect capturing time-dependent hydrolysis behavior of PAM since the adsorption

was allowed at neutral pH where the hydrolysis reaction occurs relatively slowly The solution

pH was then adjusted to the selected target value pH 3 6 or 115 Note that the simulated

surface is negatively charged at all tested pH conditions similar to the actual silica tetrahedral

sheet of montmorillonite However the charge density may be different

A model RC2 multichannel ellipsometer fabricated by J A Woollam Co Inc (Lincoln

NE) having a maximum spectral range from 075 to 515 eV and operating on the dual rotating

compensator principle (Chen et al 2004) was used for this study Ellipsometric spectra (in Δ ψ)

are collected at room temperature (20 plusmn 1degC) via real-time spectroscopic ellipsometry (RTSE)

62

Detector

Polarizer

Analyzer

Simulated Surface

Polymer

Layer

Thickness

Subjected to pH change

after polymer placementLaser

Light

Figure 44 Schematic of spectroscopic ellipsometry apparatus

monitoring during sample modification from reflection mode measurements at an oblique angle

of incidence of 70deg The spectral range was limited to 15 to 45 eV due to the absorption of light

by water (H2O)

The complex dielectric function spectra (ε = ε1 + iε2) or alternately the complex index of

refraction (N = n + ik) of the PAM layer and its time-dependent thickness variations were

extracted using a least squares regression analysis and an unweighted error function (Cong et al

1991) to fit the experimental RTSE data using structural models consisting of a semi-infinite c-Si

substrate 17 Aring native SiO2 PAM layer H2O structure For each sample measured ε is

obtained by fitting 10 individual SE measurements selected from the RTSE data to structural

models where the PAM thickness can vary A common parameterization for ε consisting of a

Sellmeier oscillator (Collins and Ferlauto 2005) and a constant additive term to ε1 was used In

this way a representative ε for each film is obtained which can then be used to determine the

PAM thickness for all ellipsometric spectra collected in real-time The underlying native oxide

thickness is determined from a separate measurement of each c-Si wafer in air Reference spectra

in ε for native SiO2 c-Si (Herzinger et al 1998) and H2O (Synowicki et al 2004) were used

Figure 45 shows the real part of (1 = n2 where 2 = 2nk = 0) obtained from RTSE

measurements of the PAM prepared at pH of 3 6 and 115 There appears to be little variation in

63

the PAM due to the pH of the solution and no absorption originating from the PAM is observed

in this spectral range 2= 0 1 for H2O is also shown to highlight the optical contrast present

between it and the PAM Figure 46-a shows the time-dependent PAM thickness for each

solution pH in this series over the span of one day The initial thickness d0 of the PAM layers

are different but range from 290 to 390 Aring The error on all thickness values is 4 Aring Figure 46-

b shows the percentage difference in the thickness for each layer as a function of time

determined by d = (d d0)d0 where d is the PAM thickness at a given time


solutions with pH = 3 6 and 115 Also shown is 1 for H2O

225

275

325

375

425

0 400 800 1200

Th

ick

nes

s (

Aring)

Time (minutes)

pH asymp 6

pH asymp 3

pH asymp 115

-30

-20

-10

0

10

20

30

0 400 800 1200

Th

ick

nes

s C

han

ge

Δd

d0

()

Time (minutes)

pH asymp 6

pH asymp 3

pH asymp 115

Δd = d - d0

(a) (b)


pH = 3 6 and 115

64

It appears that the PAM in the basic solution pH 115 swells by approximately 27 of

its initial value by the end of one day while the PAM in the acidic solutions pH 3 and 6 contract

by 26 and 17 respectively Closer investigation of the time dependent PAM layer thickness

show that the sample in pH 115 appears to initially decrease in the first 15 minutes by 7 then

subsequently increase throughout the remainder of RTSE monitoring The thickness of the PAM

in pH 115 saturates at about 600 minutes (10 hours) PAM in acid decreases monotonically with

time although PAM in the more acidic solution (pH 3) contracts more rapidly The contraction

rate for PAM in the pH 6 solution may be stabilizing after 900 minutes (15 hours) indicating that

a steady state may be reached PAM in the pH 3 solution does not appear to stabilize over the

measurement time

The initial difference in the layer thickness can be explained by a difference in ionic

strength due to the addition of 01M NaOH and HCl solution as a pH modifier The

concentration of Na+ at pH 115 was approximately 0006M while that of Cl- at pH 3 was

approximately 0001M which are large enough to limit expansion of PAM molecules resulting in

contracted coil conformation (Klenina and Lebedeva 1983 Aulich et al 2010 Bittrich et al

2010) Thus PAM in the absence of added ions ie at pH 6 has the maximum initial layer

thickness Assuming that no additional PAM attaches to the surface during this time for the pH

115 solution the PAM is expected to have initially contracted on the SiO2 surface but later

uncoiled resulting in the increased layer thickness After 15 minutes expansion of the PAM

molecules started to offset the initial decrease The PAM in pH 3 and 6 solutions begin

constricted and coiled near the SiO2 surface and continues to contract For the pH 6 case

however the changes in the layer thickness will stabilize over 15 hours while the PAM thickness

for the pH 3 case continues to decrease Since the layer thickness was expected to remain nearly

constant at pH 3 and 6 this unexpected time-dependent phenomenon at those pH values can be

considered with the concept of surface coverage It is well-known that adsorbed polymer layer

65

thickness decreases with increasing surface coverage and high molecular weight polymer

adsorbed on a surface slowly covers the surface (Leermakers et al 1996 Filippova 1998

Samoshina et al 2005) At all tested pH the same behavior of covering the surface occurs to

different degree due to pH-dependent charges on the PAM molecules Since surface coverage

increases with decreasing intermolecular repulsion (Leermakers et al 1996) the surface

coverage at pH 3 is the maximum leading to the minimum polymer layer thickness In theory the

surface coverage at pH 6 should be nearly the same as pH 3 However in reality PAM molecules

usually have slight negative charges at neutral pH caused by a finite degree of hydrolysis of

amide groups into acrylic acid (Kurenkov 1997) such that PAM molecules remain slightly

expanded coiled conformation

These RTSE results on the micro-scale PAM conformations were in reasonable

agreement with theory and previously found experimental results of PAM that PAM

conformation evolves from contracted coiled to extended as pH increases More importantly the

RTSE results confirm that PAM responsiveness to pH is still valid in the presence of a surface

44 Meso-Scale Characterization

The term ldquomesordquo used in this study is defined as the level of a significant number of clay-

polymer interactions ie 2 μm lt meso lt a few cm in length PAM appeared to have pH-

dependent conformational behavior even on a clay mineral surface evidenced by micro-scale

characterizations of PAM conformation at various pH values using dynamic light scattering and

spectroscopic ellipsometry In this section effects of such micro-scale conformational changes

on meso-scale CPN properties were investigated using specific surface area measurement

swelling test and hydraulic conductivity measurement These meso-scale characterizations may

reveal whether the controllable PAM conformation at the micro-scale is valid at the scale of

engineering applications

66

441 Specific Surface Area

Specific surface area is an important property of a clay mineral that determines amount of

accessible sites for polymer adsorption (Theng 1979 Liu and Zhang 2007) Specific surface

area measurements can be used as an indirect indicator of interlayer spacing of a clay mineral as

well as of polymer conformation The conformation of PAM molecules adsorbed onto particles

and interlayer surfaces varies with pH Thus a variation in specific surface area indicates a

change in the interlayer spacing resulting from the changing polymer molecule conformation

Gas adsorption and methylene blue (MB) adsorption are often used to measure specific surface

area Contrary to gas adsorption which utilizes dry samples the MB adsorption technique can be

applied to wet samples which is viable for characterization of tunable CPN synthesized using a

pH-responsive polymer and an expansive clay mineral Hence MB adsorption was used in this

study to measure the specific surface area of the synthesized CPN

The chemical formula of MB is C16H18N3SCl with a molecular weight of 31987 gmol

The thickness of a MB molecule is about 325Aring (Santamarina et al 2002b) Since the interlayer

spacing of Mt is about 22Aring only in the first stage of swelling ie short-range swelling (Theng

1979) MB molecules are readily adsorbed onto the interlayer surface and onto PAM molecules

previously adsorbed on the interlayer surface ie intercalated Therefore interlayer spacing

varying with PAM conformation was investigated through MB specific surface measurements

CPN and microcomposites were synthesized as aforementioned (Section 423) Clay

alone samples were also prepared as a comparison at the same clay content used for each system

The samples were then treated with 01M HCl and NaOH solutions to reach the target pH (pH 3

6 and 115) MB specific surface area measurement was carried out following the modified

European spot method (Kandhal and Parker 1998 Santamarina et al 2002b)

67

Interlayer spacing of clay minerals varying with PAM conformation was investigated

through specific surface area measurements The specific surface area was influenced by pH

(Figure 47) Since kaolinite has pH-dependent charges on its surface (van Olphen 1977 Ma and

Eggleton 1999) pH-dependent specific surface area for pure kaolinite dispersion was expected

Due to protonation and deprotonation the pH-dependent sites become positively charged with

decreasing pH inducing a decrease in MB adsorption (Ghosh and Bhattacharyya 2002) Two

important observations in Figure 47-a are (1) the specific surface area of kaolinite-nPAM

microcomposites is pH-dependent and (2) the extent of the changes in specific surface area of the

microcomposites varying with pH is greater than that of pure kaolinite dispersion This is likely

due to the pH-dependent charges of kaolinite as well as the pH-dependent conformational

behavior of PAM This observation confirms the ellipsometric observation that PAM is still pH-

responsive on a clay mineral surface (Figure 47) Note that the specific surface area of the

microcomposites was smaller than that of pure kaolinite dispersion at all tested pH ranges It was

previously reported that polymer adsorption onto kaolinite decreases specific surface area since

polymer molecules induce flocculationaggregation of clay particles (Nabzar and Pefferkorn

1985)

While Mt theoretically has pH-dependent charges at the particle edges these charges

represent less than 5 of the total surface charge In addition to the particle edges particle faces

were also reported to be pH-dependent representing as much as 20 of the face surface charge

(Schindler 1981 Mohan and Fogler 1997) Due to protonation and deprotonation the pH-

dependent sites become positively charged with decreasing pH and negatively charged with

increasing pH MB molecules are positively charged in aqueous solution and thus are more easily

adsorbed onto the mineral surface with increasing pH (Chen et al 1999 Ghosh and

Bhattacharyya 2002) Such a contribution to the overall surface charge could explain the

apparent increase in specific surface area from pH 3 to pH 115 (Raymahashay 1987)

68

10

20

30

40

50

1 3 5 7 9 11 13

Surf

ace

area

(m

2g

)

pH

Kaolinite

Kaolinite+nPAM

(a)

400

600

800

1000

1200

1 3 5 7 9 11 13

Surf

ace

area

(m

2g

)

pH

Mt+nPAM

Mt

(b)


Clay-to-polymer volume ratio for (a) and (b) was 625 and 2 respectively

69

In contrast to the kaolinite-PAM microcomposites an even greater increase in MB

specific surface area for CPN was observed with increasing pH It is likely attributable to the

difference in clay-to-polymer volume ratio The clay-to-polymer volume ratio for the CPN is

much smaller than that for the microcomposites ie 2 vs 625 Thus polymer molecules became

a dominant factor to determine the specific surface area of the CPN The specific surface area

increased with increasing pH For pure Mt specific surface area increased by approximately 10

from pH 6 to pH 115 while that for CPN increased by approximately 50 in the same pH range

In addition to the pH-dependency of the mineral surface it is also likely that the extended

conformation of PAM at high pH provides more available surface sites for MB adsorption

This result implies that interlayer spacings increase with extended PAM conformation at

basic pH When the polymer conformation becomes extended both the increased interlayer

spacing and the extended polymer molecules allow more MB molecules to be adsorbed onto the

interlayer surface and onto the polymer surface This increases the apparent specific surface area

Nevertheless further testing is required to demonstrate which factor(s) determines the behavior

since clay surface charge MB adsorption and PAM conformation vary simultaneously with pH

Specifically the increase in MB specific surface area at pH 115 is due possibly to (1) negatively

charged clay surfaces (2) negatively charged polymer surfaces (hydrolyzed to COO-) (3)

cationic MB molecules (C16H18N3S+) in water and (4) fully extended conformation of the

polymer

442 Swelling Test

Swelling behavior of clay minerals in the presence of moisture is often a problem in the

development and maintenance of geotechnical and geoenvironmental engineering applications

The swelling behavior depends on factors such as mineral composition grain size aggregate size

cationic exchange capacity chemical composition and concentration of the bulk fluid

70

(Shackelford et al 2000 Ashmawy et al 2002) Polymer treatment was reported to limit

swelling behavior of clay minerals (Inyang et al 2007) Therefore tunable CPN cannot only

limit the swelling behavior but also provide an additional benefit due to its controllable swelling

property For example a tunable CPN synthesized using a pH-responsive polymer and an

expansive clay can be used to filtrate waste water corresponding to its pH such that extremely

high pH or low pH waste water can be separated protecting a natural ecology Thus quantitative

understanding of swelling behavior of tunable CPN is important for engineered soil applications

Comparing swelling behavior of the microcomposites with that of CPN effects of

internal swelling can be investigated As mentioned previously kaolinite has little swelling

potential Thus only the interparticle spacing of PAM-treated kaolinite is affected

(microcomposite as in Figure 26-a) On the other hand polymer intercalation into the interlayer

space of Mt was achieved through a solution intercalation technique leading to nanocomposite

with intercalated structure (Figure 26-b) Kaolinite-PAM microcomposites and CPN were

synthesized as described in Section 423 Swelling ratio was determined by measuring water

absorbency (Vazquez et al 1997 Bajpai and Giri 2003 Mahdavinia et al 2004) The

synthesized composites in dry powder form (1g) was placed into a weighed filter bag and

immersed in 250 ml deionized water The water pH was adjusted to the target pH (pH 3 6 and

115) using 01M HCl or 01M NaOH solution The sample was allowed to hydrate with water at

room temperature At consecutive time intervals the filter bag containing the swollen sample

was allowed to drain by hanging until water drops no longer fell from the sample (~20 minutes)

The bag was then weighed to determine the mass of the swollen gel The swelling ratio was

calculated by dividing the mass of the swollen sample by the mass of the dry sample

71

0

1

2

0 24 48 72

Sw

elli

ng r

ati

o

Time (hour)

pH 115

pH 6

pH 3

(a)

0

5

10

15

0 24 48 72

Sw

elli

ng r

ati

o

Time (hour)

pH 115

pH 6

pH 3

(b)


dashed lines indicate the swelling ratios for the untreated (no polymer) materials

Untreated

Kaolinite

Untreated

Mt

72

The swelling ratio determined by measuring water absorbency is shown in Figure 48

The swelling ratio tends to increase with time at all tested pH until reaching equilibrium but the

magnitude differs significantly After 72 hours the microcomposites and the CPN at pH 115

have swelling ratio of 145 and 129 respectively while those at pH 3 have swelling ratio of

approximately 11 and 38 respectively As expected the PAM hydrolysis rate was greater under

a basic condition (Kheradmand et al 1988 Kurenkov 1997) The measured degree of

hydrolysis for the polymer at pH 115 was 081 which is in good agreement with reported

experimental values of maximum degree of hydrolysis (Kurenkov 1997 Huang et al 2001)

The difference in swelling ratio between samples at pH 3 and 6 was expected to be insignificant

since little ionization occurs at pH below pH 85 ie about 2 units lower than the pKa value

However PAM hydrolysis at neutral pH as well as the addition of 01M HCl solution to adjust

the solution pH may have contributed to the observed difference seen in both the microcomposite

and the CPN

In spite of previously reported results that polymer treatment limits swelling behavior

(Inyang et al 2007) this result implies that conformational changes of PAM adsorbed in the

interlayer space lead to interlayer spacing changes However the magnitude of internal swelling

and external swelling due to PAM conformation change cannot be separated since the surface

characteristics of kaolinite and Mt are different from each other Nevertheless these results

indicate that both interlayer and interparticle spacings can be modified by a pH-responsive

polymer Another important finding from the results is that the swelling property of clay-polymer

composites synthesized with a pH-responsive polymer can be controlled by altering the pH

condition such that the swelling is either less than or greater than that of the untreated material

Note that swelling ratios for untreated clay minerals were obtained from swell index

(ASTM D5890) (2006) The swelling ratio for untreated clay minerals was volumetric ratio of

the soil sample before and after the sample is immersed in deionized water for 72 hours

73

Equilibrium swelling ratios for untreated clay minerals was reached after 24 hours The swelling

ratio for untreated kaolinite was 1 at all tested pH conditions while that for untreated Mt was

117 12 and 115 at pH 3 6 and 115 respectively It was previously reported that Mt swelling

decreased with increasing ionic strength (Herbert et al 2008) Thus the slightly pH-dependent

swelling ratio for pure Mt is likely attributed to increased ionic concentration by adding 01M

HCl or NaOH solution as a pH-modifier Expansion of polymer conformation is also limited by

high ionic strength at highlow pH (Aulich et al 2010 Bittrich et al 2010) Thus the same

effect likely occurred in the swelling ratio measurement for the microcomposites and the CPN

However when comparing the extent of PAM conformation changes the effect of increased ionic

strength was insignificant after equilibrium is reached

443 Hydraulic Conductivity Measurement

Hydraulic conductivity (permeability) which is one of most important characteristics in

the field of geotechnical and geoenvironmental engineering is affected by fabric anisotropy pore

fluid chemistry mineral type including particle size size distribution and chemical composition

internal swelling saturation and compaction method of a soil system (Mitchell 1993) Different

fabric types for kaolinite and Mt lead to different permeability values (Mitchell 1956 Suarez et

al 1984) For example open fabric (eg edge-to-face and edge-to-edge) systems have two

orders of magnitude greater permeability than closed fabric (eg face-to-face and dispersed)

systems Internal swelling of clay soil systems decreases permeability (Jo et al 2001) and can be

limited by treating with a polymer (Inyang et al 2007) Polymer adsorption onto clay particles

occurs at the external surface and internal surface (ie intercalation) altering the fabric type and

the interlayer spacing Thus the effect of fabric type and internal swelling is of concern in this

study

74

Hydraulic conductivity tests were conducted to investigate pH-dependent meso-scale

behavior of kaolinite-PAM microcomposite and CPN materials Permeability of the

microcomposites and the CPN should decrease with increasing pH since PAM extends under high

pH conditions resulting in swelling of the composites Consequently the surrounding pore size

reduces A reduction in the pore size prevents water flow through the system thus decreasing

permeability (Gardner and Arias 2000 Shackelford et al 2000 El-Hajji et al 2001 Jo et al

2001) Effects of sample type polymer molecular weight (MW) and ionic type of polymer were

also investigated Two different sample types ndash gel-form and powder-form ndash were used Three

different PAM ndash low MW nonionic PAM high MW nonionic PAM and high MW cationic PAM

ndash were used

A pressurized permeameter was used for this study The permeability test apparatus

included a confining pressure cell and equipment for supplying a driving pressure greater than

ambient pressure to the sample (Figure 49) This pressurized permeability test (Plaks 2010) was

adopted to minimize the measurement time and preferential flow The permeability cell consists

of a hollow metal cylinder which holds a Tygon tube with an inner diameter of 254 cm Clay-

polymer composites of 23 g were synthesized in either gel-from or powder-form using three

different PAM ie low MW PAM high MW nonionic PAM and high MW cationic PAM Thus

total number of samples was 16 including untreated (no polymer) kaolinite and Mt The

synthesized materials were placed in the Tygon tube and then compacted using a tamping rod

until the packed sample length is 4 cm so the void ratio of the sample is 05 A confining

pressure of 50 lbin2 and a driving pressure of 25 lbin2 were applied though high pressure

permeant lines connected to the permeability cell The permeant solution was pH-adjusted

deionized water The pH was adjusted to pH 3 6 or 115 using 01M HCl or 01M NaOH

solution A test at one pH condition was run until the effluent pH and electrical conductivity

reached equilibrium Effluent pH and electrical conductivity were monitored at consecutive time

75

Pressure

Control PanelGas

Supply

Influent

Solution Reservoir

Driving Pressure

Confining

PressurePermeability

Cell

Effluent

Collector


cell

intervals After replacing the influent solution with next target pH another permeability

measurement was conducted on the same sample Once a cycle of permeability tests with four

pH conditions (pH 6 pH 3 pH 6 pH 115) was completed the sample was replaced

Sample calculations for permeability can be found in Appendix B Note that a permeability of

1x10-10 cms was the experimental minimum of the test apparatus

Figure 410 shows the hydraulic conductivity test results for kaolinite-PAM

microcomposites as a function of pH Permeability tends to decrease with increasing pH for all

tested samples Due to pH-dependent surface charges of kaolinite pure kaolinite has a slightly

pH-dependent permeability The pH-dependent surface leads to dispersed fabric at high pH

resulting in low permeability (Mitchell 1956 Santamarina et al 2001 Palomino and

Santamarina 2005) For the microcomposites polymer adsorption induced flocculation or

aggregation of kaolinite particles leading to larger pore sizes in the system Kaolinite-NPAM

microcomposites have the greatest permeability since high molecular weight PAM links more

kaolinite particles leading to larger flocsaggregates ie larger pore size Greater decreases in

76

permeability for the microcomposites with increasing pH than the case of pure kaolinite were

observed (Figure 410-a) Since PAM conformation becomes extended at high pH these

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bil

ity

(cm

s)

pH

Kaolinite+nPAM

Kaolinite+NPAM

Kaolinite+CPAM

Kaolinite

(a)

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bil

ity

(cm

s)

pH

Kaolinite+nPAM

Kaolinite+NPAM

Kaolinite+CPAM

Kaolinite

(b)


and (b) powder-form

77

decreases in permeability were likely due to PAM-induced pore size reduction For kaolinite-

CPAM microcomposites the magnitude of permeability changes with pH differs from other

microcomposites since cationic PAM molecules preferentially link negatively charged kaolinite

particles reducing the expansion of PAM molecules The ion-ion interaction between a kaolinite

particle and a CPAM molecule is even stronger than the ion-dipole interaction between a

kaolinite particle and a nPAMNPAM molecule (Ebnesajjad 2006)

For the microcomposites in powder form (Figure 410-b) permeability decreased to a

lesser degree when treated with PAM This is attributed to mechanical degradation of PAM

molecules when ground (Kulicke et al 1982) Since the air-dried microcomposites were ground

into nearly same sized particles PAM molecules adsorbed on the kaolinite surfaces were trimmed

to nearly same sized chains Thus all three types of kaolnite-PAM microcomposites appear as

having nearly the same permeability at pH 3 and 6 At pH 115 slightly higher permeability of

kaolinite-CPAM microcomposites was observed due to wholely negatively charged kaolinite

surfaces Kaolinite particles become negatively charged on both silica and aluminum sheets at

pH gt 8 since the isoelectric point for the face and edge of kaolinite particle is about pH 79 and

pH 72 respectively (Santamarina et al 2001 Tekin et al 2005)

Figure 411 shows the hydraulic conductivity test results for CPN as a function of pH

Permeability tends to decrease with increasing pH for all tested samples Due to pH-dependent

surface charges of Mt pure Mt has slightly pH-dependent permeability As pH decreases the

particle edges become positively charged while the particle faces still remain negatively charged

inducing electrostatic attraction between the edges and faces ie edge-to-face flocculation

(Lagaly 1989 Mohan and Fogler 1997)

For CPN polymer adsorption induced flocculationaggregation of Mt particles leads to

larger pore sizes in the system Mt-nPAM nanocomposites have the greatest permeability which

is different from the case of kaolinite-PAM microcomposites This implies that internal swelling

78

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bilit

y (

cms

)

pH

Mt+nPAM

Mt+NPAM

Mt+CPAM

Mt

(a)

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bilit

y (

cms

)

pH

Mt+nPAM

Mt+NPAM

Mt+CPAM

Mt

(b)

Figure 411 Permeability of CPN as a function of pH (a) gel-form and (b) powder-form

as well as fabric type plays a significant role in permeability nPAM was found to be most

readily intercalated into the interlayer space of Mt thus Mt-nPAM nanocomposites are likely to

79

have the greatest ability for permeability modification by pH changes Greater decreases in

permeability for CPN with increasing pH than the case of pure Mt were observed (Figure 411-a)

Since PAM conformation becomes extended at high pH the greater decreases in permeability

were likely due to PAM-induced pore size reduction For Mt-CPAM nanocomposites the

different magnitudes of the pH-dependent permeability changes from other CPN is because

cationic PAM molecules preferentially link negatively charged Mt particles hindering an

expansion of PAM molecules

For the CPN in powder form (Figure 411-b) permeability decreased to a lesser degree

All three types of CPN appeared to have nearly the same permeability at pH 3 and 6 Like to the

microcomposites this is attributed to mechanical degradation of PAM molecules when ground

(Kulicke et al 1982) At pH 115 higher permeability of Mt-CPAM nanocomposites was due to

the higher affinity of cationic PAM molecules to the negatively charged Mt surfaces

45 Linkage of Micro-Scale Behavior to Meso-Scale Property

It was observed that the micro-scale polymer conformation influenced meso-scale CPN

properties including specific surface area swelling potential and permeability From the

evidence of DLS and SE measurements the coiled polymer conformation at pH 3 becomes

expanded coiled at pH 6 and further extended with increasing pH (pH 115) Meso-scale CPN

properties were affected by the pH-dependent PAM conformation Specific surface area

increased with extended conformation of PAM while it decreased with coiled conformation of

PAM Swelling potential also increased with increasing pH ie extended conformation of PAM

The increase in swelling potential of CPN induced a decrease in pore size in the CPN system

resulting in decreased permeability

In comparing hydrodynamic radius measurements obtained from DLS to adsorbed PAM

layer thickness measurements obtained from SE a qualitative agreement was found that both

80

hydrodynamic radius and adsorbed PAM layer thickness increase with increasing pH (Figure

412) According to scaling law theory (de Gennes 1987) the maximum possible hydrodynamic

thickness for PAM is 12181 nm assuming one layer adsorption of PAM on the surface However

the adsorbed thickness at pH 115 was approximately 375 nm Such a discrepancy may result

from many factors affecting the polymer comformation including ionic strength due to the

addition of pH modifiers crosslinking effect and intra-interactions of the polymer and

interactions between polymers and surfaces (Klenina and Lebedeva 1983 de Gennes 1987

Askadskii 1990 Fleer 1993 Lee et al 1999 Wu et al 2001 Aulich et al 2010 Bittrich et al

2010) Note that the scaling law theory does not provide any insight into the conformation of the

polymer adsorbed on a surface (Campbell et al 2002) The same discrepancy was observed

when comparing conformational behavior of the polymer at two different scales ie adsorbed

PAM layer thickness vs swelling ratio (Figure 413) However a qualitative agreement was

found between the adsorbed PAM layer thickness and the swelling ratio

0

10

20

30

40

0

20

40

60

80

100

1 3 5 7 9 11 13

Ad

sorb

ed P

AM

Lay

er T

hic

kn

ess

(nm

)

Hy

dro

dy

nam

ic R

adiu

s (n

m)

Solution pH

Hydrodynamic radius of PAM

Adsorbed PAM layer thickness



layer thickness was obtained from spectroscopic ellipsometry

81

0

5

10

15

0

10

20

30

40

1 3 5 7 9 11 13

Sw

elling

R

atio

Ad

sorb

ed P

AM

Lay

er T

hic

knes

s (n

m)

Solution pH


Swelling ratio



was measured using water absorbency tests

The extent of conformation changes was likely to be affected by the presence of a clay

surface Based on DLS results PAM layer thickness should increase by approximately 100

from pH 6 to pH 115 However the layer thickness of PAM adsorbed on a surface increased by

approximately 20 (Figure 412) Similar phenomenon was also observed for PAM sandwiched

in between two surfaces (Figure 47) Based on the surface area of a PAM molecule calculated

using hydrodynamic radius the surface area of a PAM molecule increases by approximately

500 from pH 6 to pH 115 in a bulk aqueous solution However surface area contribution of

PAM molecules to the increase in CPN specific surface area was approximately 50 Thus the

conformational behavior of PAM was further limited when it is adsorbed in between two surfaces

These phenomena can be explained by the previously reported observation that the logarithmic

value of the acid dissociation constant pKa inside a polymer molecule is different from the pKa

value near a surface (Dong et al 2009) Possible reasons for this gradient include minimization

82

of the systemsrsquo free energy and inhomogeneous polymer volume distribution or the formation of

a double layer at the polymer-solution interface reducing the ion transport into the polymer

molecule (Uhlik et al 2004 Gong et al 2007)

Yet a quantitative linkage between the micro-scale PAM conformation and the meso-

scale properties cannot be made due to (1) many factors affecting the behavior simultaneously

and (2) experimental limitations of characterizing the location of polymer molecules in CPN ndash

either in the interlayer spacing or on the particle surface Computer simulation providing a

molecular level understanding of the mechanisms responsible for the behavior of clay-polymer

systems can be an alternative to capture the PAM behavior in the interlayer spacing of CPN

Such a technique is expected not only to complement experimental results with a detailed micro

level picture of the relevant phenomena but also to illuminate systems inaccessible via current

experimental methods

46 Conclusions

In this chapter micro-scale conformational behavior of a pH-responsive polymer was

qualitatively linked to meso-scale properties of clay-polymer nanocomposites (CPN) including

specific surface area swelling potential and permeability The micro-scale polymer

conformation studied by dynamic light scattering (DLS) and real-time spectroscopic ellipsometry

(RTSE) was in a reasonable agreement with the measured specific surface area swelling potential

and permeability of the CPN

The conformation of polyacrylamide (PAM) in an aqueous solution varied with pH from

coiled (pH 3) to extended (pH 115) Corresponding to the conformational changes layer

thickness of PAM adsorbed on a surface meso-scale properties of the synthesized clay-polymer

composites including specific surface area swelling potential and permeability were modified by

altering the pH condition The layer thickness specific surface area and swelling potential

83

increased significantly with increasing pH corresponding to the extended conformation of PAM

at basic pH The increase in swelling potential reduced the pore size leading to a decrease in

permeability In the presence of a surface the conformational changes were limited However a

quantitative linkage was not made due to experimental limitations and complex pH-dependencies

of clay surface charge and PAM conformation

Nevertheless the effectiveness of the use of a pH-responsive polymer has been

established in this chapter Understanding the kinetics of PAM conformational behavior on a

simulated surface verified by specific surface area swelling potential measurements and

permeability tests on real CPN will assist in developing strategies for designing CPN with tunable

engineering properties

84

Chapter 5

COMPUTER SIMULATION

The purpose of this chapter is to computationally investigate responsiveness or tunability

of clay-polymer nanocomposites (CPN) with controllable micro-scale interlayer and interparticle

spacing since quantification is limited with current experimental techniques The quantitatively

found computer simulation results will be linked to an experimentally measured property of the

CPN Descriptions of computational procedures and their interpretation are provided

quantitatively verifying that the micro-scale conformational changes of polymer lead to meso-

scale property changes

51 Introduction

In spite of the considerable number of studies of CPN clay intercalation by polymer is

not yet fully understood Due to many factors affecting the process and difficulties of developing

tools capable of monitoring the process quantifying final morphology and properties of the final

CPN is very challenging In addition nearly amorphous characteristics of clay minerals and the

interactions responsible for meso-scale properties occurring at the length scales of monomers

approximately a billionth of a meter limit probing with current experimental techniques

Understanding the conformational behavior of a responsive polymer adsorbed on a surface is

critical to predicting the behavior of tunable CPN Thus computer simulation may play an ever-

increasing role in designing and predicting material properties and designing such experimental

work

Computer simulation can provide insight into the molecular level understanding of the

mechanisms responsible for the behavior of clay-polymer systems All forces and interactions

occurring at the micro-level can be simulated through mathematical equations Such a technique

not only complements experimental results with a detailed atomistic level picture of the relevant

85

phenomena but also illuminates systems unaccessible via experimental methods Computer

simulation of clays and polymers based on theories and computational methods have long been

used to study and understand their complex behavior (Chang et al 1995 Skipper et al 1995

Boek et al 1996 Groot and Warren 1997 Sposito et al 1999 Balazs et al 2000 Bourg et al

2003 Cygan et al 2004b Pandey et al 2005 Sutton and Sposito 2006 Suter et al 2009) The

purpose of this study is to investigate pH-dependent conformational behavior of a polyacrylamide

(PAM) in an aqueous solution and to link the micro-scale conformational changes to a meso-scale

CPN property Dissipative particle dynamics (DPD) a coarse-grained atomistic computer

simulation technique was used to simulate micro-scale CPN behavior Three different conditions

were simulated (1) polymer in an aqueous solution (2) polymer adsorbed on a clay layer surface

and (3) polymer sandwiched between two clay layers An attempt was made to link the

composite response predicted with DPD to the experimentally measured CPN properties under

similar pH conditions

52 Mapping of Length- and Time Scales

In a DPD simulation it is necessary to map physical length and time scales with reduced

units in order to match the simulated system behavior with actual system conditions Groot and

co-authors (Groot and Warren 1997 Groot and Rabone 2001) report that the distance beyond

which all forces become zero the so-called cutoff radius is always unity Thus when

representing more than a single water molecule with a single DPD bead Groot et alrsquos

parameterization often fails For example an increase in the repulsion parameter led to freezing

of a DPD liquid This represents an upper limit of coarse-graining (CG) (Pivkin and Karniadakis

2006) An alternative CG method was developed such that the cutoff radius can be adjusted

(Fuchslin et al 2009) This method prescribes enlarging the interaction radius of DPD beads

while decreasing the number of DPD beads in a system Using this method a simple monomeric

86

DPD system with a CG level of up to 125 was simulated without changing the pressure or mass

density of the system This alternative method of coarse-graining was adopted for this study

The scaling relations for the CG level number mass and cutoff radius of DPD beads DPD force

constants and energy and time units are listed in Table 51

The density and the number of atoms to be coarse-grained into a DPD bead influence the

mapping between physical and reduced length- and time scales In this study =1 represents a

system in which one water molecule is coarse-grained into a DPD bead Thus simulation

parameters for =1 are rc=1 m=1 α=25 γ=45 σ=3 and ε=1 (Groot and Warren 1997) These

parameters imply that each DPD bead has a volume equal to the volume of a water molecule (asymp

30 Aring 3) hence rc = 4481 Aring at mass density ρ=3 (Groot 2003) These parameters are scaled

according to the described scaling relations for other coarse-graining levels For example for

=12 simulation parameters should be rc=12 m=12 α=131037 γ=23587 σ=23792 and ε=12

Table 51 Scaling relations used in this study (Fuchslin et al 2009)

Scaling ratio = 1 Scaling ratio =

Total number of DPD beads N -1 N

Mass m m

Cutoff radius rc 1d rc

Force constant α 1-1d α

Friction coefficient γ 1-1d γ

Noise amplitude σ 1-1(2d) σ

Energy unit ε ε

Time unit τ 1d τ

d is the number of dimensions of the system

87

53 Polyacrylamide in an Aqueous Solution

The first step in this study was to investigate the polymer conformation with various

charge fractions in an aqueous solution The DPD method has been successfully used to simulate

the conformation of charged polymers (Gonzalez-Melchor et al 2006) Gonzalez-Melchor et al

found that the root mean square radius of gyration which represents the morphology of polymer

molecules increases with increasing charge fraction on the polymer chain in an aqueous solution

Thus the root mean square radius of gyration was used to monitor the conformation of the

polymer with eight different charge fractions 0 01 0143 02 025 033 05 and 08 The

charge fraction was defined as the number of charged beads with respect to the total number of

beads composing the polymer molecule Hence the difference in charge fraction was simulated

by increasing the number of charged beads on a polymer chain The maximum charge fraction

was set to 08 since the maximum degree of hydrolysis of polyacrylamide is 80 (Kurenkov

1997 Huang et al 2001) In order to remove the effect of ionic strength which has been reported

to influence polymer conformation (Fleer 1993) the ionic concentration was kept at zero by not

adding any salts beads

The system considered here includes a long chain of polymer molecules with charges

counterions and water molecules Each of these components was modeled explicitly A cubic

simulation box of size 50 x 50 x 50 in DPD length units was employed The DPD parameters

used in this study are found in Tables 52 and 53 The overall mass density of the system was

held constant at ρm = 3 For a system with 1 the force constant between like beads was

determined as αii = 75ρm (Groot and Warren 1997) The force constant between unlike beads

αij was determined as (Groot 2000)

αij = αii + 3268middotχij

where αii is the force constant between like beads and χij is the Flory-Huggins parameter which is

048plusmn001 for the given polymer in water at 30degC (Huang et al 2001) The force constant was

88

Table 52 DPD parameters used in this study

= 1 = 12

Mass 1 12

Mass density 3 3

Number density 3 025

Cutoff radius 1 2289

γ 45 23587

σ 3 23792

ε 1 12

τ 1 2289

Table 53 Force constants α used in this study

water

Non-

charged

PAM

Charged

PAM

Non-

charged

clay

Charged

Clay Counterion

water 13104 13261 10483 13261 4717 13104

Non-charged

PAM 13104 13104 4717 1048 13261

Charged PAM 13104 1048 13261 13261

Non-charged

clay 13104 13104 13261

Charged Clay 13104 13261

Counterion 13104

also calculated based on the solvency of each component as (Kong et al 1997 Gibson et al

1998)

αij = αii (1 + ζ)

89

where ζ is the solvency of the solvent The theta-solvent condition (random coil conformation)

occurs at ζ=0 The solvency between water and polyacrylamide was set to -002 to reflect the

water-soluble nature of the polymer (Gibson et al 1998)

DPD parameters for a system with 12 were calculated according to Fuchslinrsquos scaling

relations shown as above (Fuchslin et al 2009) This scaling ratio was selected in the

consideration of efficiency and accuracy At this scaling ratio a 236-bead polymer corresponds

to mapping polyacrylamide (PAM) with molecular weight Mw=80000

A constant time step of Δt = 004 was used so that the investigation of the equations of

motion remained stable and the average temperature of the system did not exceed a system

temperature plusmn2 All simulations were performed using the LAMMPS molecular dynamics

simulator (Plimpton 1995) A simulation was run for 500000 time steps to reach equilibrium

followed by another 500000 time steps to calculate average properties of the system

One polyacrylamide molecule in water was simulated at eight different charge fractions

The main result of this type of simulation is the root mean square radius of gyration ltRg2gt12 of

the polymer in the solution as a function of charge fraction The radius of gyration is a key

property that varies with polymer conformation which has been studied both theoretically and

experimentally (Francois et al 1979 Medjahdi et al 1990 Stigter and Dill 1995 Griffiths et

al 2004) The root mean square radius of gyration was calculated by

i

cmiig rrmM

R 2212)(

1

where M is the total mass of polymer molecule mi and ri are the mass and position of ith

monomer and rcm is the center-of-mass position of the molecule Since the conformation of

polyacrylamide varies with pH the radius of gyration should also vary with pH pH of the

simulated solution was calculated with the Henderson-Hasselbalch equation (Katchalsky and

Spitnik 1947)

90

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

3

4

5

5 7 9 11 13

ltR

g2gt

12

pH

(b)


pH

91

apKc

cpH

)

1(log10

where c is charge density and pKa is the logarithmic value of the acid dissociation ndash acidity ndash

constant (108 for polyacrylamide) Simulated root mean square radius of gyration results of the

polymer are shown in Figure 51

Figure 51-a shows the results for the root mean square radius of gyration as a function of

charge density The trend is in good agreement with experimental results (Stigter and Dill 1995)

Figure 51-b shows the pH-dependent root mean square radius of gyration The radius of gyration

abruptly changed around the pH value of the polymerrsquos pKa which qualitatively corresponds to

experimental results (Griffiths et al 2004) Note that pH values of 1 and 14 correspond

theoretically to the fully coiled and fully extended polymer conformation respectively (Stigter

and Dill 1995) In order to confirm that the apparent increase in the root mean square radius of

gyration between charge density 025 and 033 plots of ltRg2gt12 vs simulation time intervals are

displayed in Figure 52 Figure 52 also demonstrates that the used time step of 500000 for

equilibrium was appropriate for the studied system

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

(a) (b)

Figure 52 ltRg2gt12 vs simulation time for PAM with charge density of (a) 025 and (b) 033

92

54 Polyacrylamide Adsorbed on a Clay Particle

After investigating the conformational behavior of the polymer in an aqueous solution

the conformation of adsorbed polymer on a clay particle was explored using the DPD method A

polymer molecule and a clay layer were placed in a cubic simulation box of size 50 x 50 x 50 in

DPD length units The clay layer was tethered at the bottom of the simulation box (z=1) by a stiff

harmonic spring A system containing the polymer molecule with no charges and the clay layer

were simulated for 500000 time steps allowing adsorption of the polymer molecule onto the clay

layer surface Another 500000 time steps were run at each selected polymer charge fraction to

collect average properties of the system Z-coordination and root mean square radius of gyration

of the polymer were monitored In order to isolate the conformational behavior of PAM the clay

surface charge density was fixed at 02 which is a typical charge fraction for a montmorillonite

(Mt) surface

The z-coordination and root mean square radius of gyration of a PAM molecule as well

as the conformational behavior of the PAM molecule adsorbed on a clay surface were

investigated Simulated results of root mean square radius of gyration of the polymer and the

polymer layer thickness ie averaged z-coordination of the polymer are shown in Figure 53


charge density The trend is in good agreement with that for the polymer in an aqueous solution

(Figure 51-a) However there appear to be slight differences between this case and the polymer

molecule in solution alone The difference may be attributed to the interactions between the

surface and the polymer which induced a bulk pKa value inside the polymer molecule different

from the pKa value near the surface (Uhlik et al 2004 Gong et al 2007 Dong et al 2009) At

pH 85~10 the expected force on the polymer molecule is repulsion so that the conformation is

expanded-coiled At pH gt 10 the expected repulsive force on the polymer molecule further

increases and the corresponding conformation also increases leading to the maximum polymer

93

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Poly

mer

Lay

er T

hic

knes

s

pH

(b)


layer thickness as a function of pH

94

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)




neutral clay and charged clay

95

layer thickness The adsorbed polymer layer thickness also varies with solution pH (Figure 53-

b) The results shown in Figure 53-b confirm that PAM molecules remain pH-responsive when

adsorbed on a clay surface Figure 54 graphically shows that the polymer layer thickness varied

according to conformational changes of the polymer due to different charge densities The

polymer layer thickness increases near the pKa value of the polymer

55 Interlayer Spacing Manipulation

Interlayer spacing between two clay layers was monitored with varying polymer charge

fraction A polymer molecule and two clay layers were placed in a cubic simulation box of size

50 x 50 x 50 in DPD length units One clay layer was tethered at the bottom of the simulation

box (z=1) by a stiff harmonic spring and the other clay layer was placed at z=10 so that the initial

interlayer spacing was approximately 40Aring which is the experimental maximum interlayer

spacing of montmorillonite (van Olphen 1977) A system containing the polymer molecule with

no charges was sandwiched between the clay layers and simulated for 500000 time steps

allowing adsorption of the polymer molecule onto the two clay layer surfaces Another 500000

time steps were run at each polymer charge fraction to collect average properties of the system

The z-coordination of the top clay layer and root mean square radius of gyration of the polymer

were monitored The clay surface charge density was fixed at 02 The effect of clay-to-polymer

volume ratio was also simulated by increasing the number of polymer molecules One and two

polymer molecules represent clay-to-polymer volume ratio of 4 and 2 respectively

Z-coordination of the top clay layer and root mean square radius of gyration of the

polymer were monitored to investigate interlayer spacing manipulation Interlayer spacing was

calculated by averaging the z-coordination of the top clay layer Simulated results of the root

mean square radius of gyration of the polymer and the interlayer spacing are shown in Figure 55

96

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

pac

ing

pH

(b)


interlayer spacing as a function of pH at clay-to-polymer volume ratio 4

Figure 55-a shows results for root mean square radius of gyration as a function of charge

density The trend is in good agreement with that for the polymer in an aqueous solution (Figure

97

51-a) while a slight difference appeared due to the presence of two clay layer surfaces Interlayer

spacing tends to increase with pH (Figure 55-b) showing the tunability of the clay-polymer

nanocomposites The polymer layer thickness with only one clay layer surface (Figure 53-b) was

greater than the case with two clay layers In other words the polymer layer thickness ie

interlayer spacing decreased with the two clay layer surfaces Interactions between the surfaces

and the polymer induced a difference in the pKa value between inside the polymer molecule and

near the surface (Uhlik et al 2004 Gong et al 2007 Dong et al 2009) The extent of the

difference in pKa value further increased with the two clay layer surfaces Figure 56 graphically

shows final trajectories of the polymer and the clay layers The interlayer spacing varied

according to conformational changes of the polymer due to different charge densities An abrupt

change occurs in the interlayer spacing near the pKa value of the polymer ie charge density 05

(Figure 56-h)

98

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)






99

Clay-to-polymer volume ratio has been reported to be a critical factor for the intercalated

structure formation (Kim and Palomino 2011) The quantity of intercalated structure increases

with decreasing clay-to-polymer volume ratio enhancing the ability for further modification

Effects of clay-to-polymer volume ratio were investigated with clay-to-polymer volume ratios of

2 and 4 Simulated results of the root mean square radius of gyration of the polymer and the

interlayer spacing at clay-to-polymer volume ratio 2 are shown in Figure 57 The trend is nearly

the same as at clay-to-polymer volume ratio 4 However an increase in the interlayer spacing

was observed at charge density greater than 033 It is well-known that crosslinking polymer

molecules affects polymer conformation in dilute solutions (Askadskii 1990 Fleer 1993 Lee et

al 1999 Wu et al 2001) Thus the observation is likely due to the relative increase in the

number of polymer molecules At high charge density the repulsion forces generated by two

polymer molecules ndash clay-to-polymer volume ratio 2 ndash are greater than those with one polymer

molecule ndash clay-to-polymer volume ratio 4 ndash such that the interlayer spacing further increased

This phenomenon is in good agreement with previously reported experimental results and that

the potential for further modification increases with decreasing clay-to-polymer volume ratio

(Kim and Palomino 2011)

100

1

2

3

4

5

6

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

pac

ing

pH

(b)


the interlayer spacing as a function of pH at clay-to-polymer volume ratio 2

101


It was quantitatively found that PAM conformation becomes extended with increasing

pH inducing an increase in the interlayer spacing of a clay mineral However this result for one

PAM-molecule system cannot be quantitatively linked to the experimental findings described in

Chapter 4 since in reality it is difficult to test with one PAM molecule For example 17x1014

PAM molecules are theoretically contained even at a very small concentration of PAM (eg 15

ml of 15 mgL PAM solution which was used in the DLS tests) In addition crosslinking

polymer molecules affects polymer conformation in dilute solutions (Askadskii 1990 Fleer

1993 Lee et al 1999 Wu et al 2001) Hence a quantitative linkage between computer

simulation results and experimental results often fail Yet it is still worth attempting to

qualitatively link the computational results to the experimental findings

In addition to the measurement conducted in Chapter 442 the same test was carried out

at five different pH values to match with simulated pH intervals The additionally tested pH

values were pH 112 108 102 84 and 38 Results of swelling ratio at 72 hours as well as the

simulated interlayer spacing are presented in Figure 58 The simulated results of interlayer

spacing is in a good qualitative agreement with the experimental swelling ratio In other words

PAM conformation changes to extended with increasing pH However a significant change in

the swelling ratio occurs around pH 113 On the other hand the simulated results show that such

a significant change in the interlayer spacing occurs near the pKa value of the polymer (ie pH

108) This is attributed to not only the change in the pKa value of the polymer near the surface

but also the lowered pH value near the surface (Michaels and Morelos 1955 Uhlik et al 2004

Gong et al 2007 Dong et al 2009)

102

0

10

20

30

40

50

0

5

10

15

1 3 5 7 9 11 13

Sim

ula

ted

Inte

rlay

er

Spac

ing

Sw

elling R

atio

Solution pH

Swelling ratio

Simulated interlayer spacing



respectively The CPN was synthesized at clay-to-polymer volume ratio 2

Contrary to the observations from DPD simulations of the interlayer spacing that the

PAM conformations were nearly the same at pH below 8 the swelling ratio significantly

increased from pH 3 to pH 84 This phenomenon may be attributed to the nature of Mt and

PAM The charge fraction for the simulated clay surfaces was fixed at 02 (pH-independent) to

isolate the conformational behavior of PAM while natural Mt has pH-dependent charges on its

surface The results of specific surface area and permeability for Mt confirm the pH-dependent

behavior of Mt (Figures 43 and 45) In addition PAM molecules usually have slight negative

charges at neutral pH caused by a finite degree of hydrolysis of amide groups into acrylic acid

(Kurenkov 1997) Thus it is likely that the combination of those mechanisms induced a

significant change in swelling ratio from pH 3 to pH 84

DPD simulations and physical experiments are mutually supportive Experimental

limitations precluded obtaining a permeability measurement for CPN at pH 115 as the

103

permeability was too low to measure However DPD simulation results provide insight into the

permeability at pH 115 The expected permeability would further decrease due to more extended

interlayer spacing (Figure 55-b) On the other hand a system is often simplified for the

efficiency of computer simulation so some characteristics are not captured In this study the use

of simplified clay surfaces and polymer molecules did not capture pH-dependent behavior of Mt

and the hydrolysis behavior of PAM at neutral pH

57 Conclusions

In this study the coarse-grained atomistic computer simulation technique of dissipative

particle dynamics was used to quantitatively explore the effect of micro-scale pH-responsive

polymer conformation on the interlayer spacing of clay-polymer nanocomposites (CPN)

Polyacrylamide (PAM) and montmorillonite (Mt) surface were modeled as a bead and harmonic

spring The pH-responsiveness of the polymer was simulated by using various charge fractions

The polymer conformation became extended with increasing pH The same trend was observed

with clay surfaces to a lesser degree A quantitative relationship between the PAM conformation

and the interlayer spacing of the simulated clay was found for a system containing one PAM

molecule sandwiched in between two Mt layers

Swelling ratio was measured to link the micro-scale PAM conformation to meso-scale

CPN properties The swelling ratio results were in qualitative agreement with the simulated PAM

conformation in that the swelling ratio increased with increasing pH The computer simulation

results confirmed that micro-scale changes in polymer conformation of tunable CPN affect meso-

scale CPN behaviors

Although it is still challenging to quantitatively link computational findings to

experimental results computer simulation was demonstrated to be a viable tool providing a good

qualitative agreement with experimental findings In addition computer simulation provided the

104

insight to overcome experimental limitations On the other hand experimental results provided

information that computer simulation did not capture such as pH-dependent behavior of

montmorillonite crosslinking effects of the polymer and hydrolysis behavior of PAM at neutral

pH

105

Chapter 6

CONCLUSIONS

A new technique of soil modification with the use of a responsive polymer ndash tunable

clay-polymer nanocomposites (CPN) ndash was developed and demonstrated in this study The

tunable CPN were proven to have controllable system properties by means of further

modifications post synthesis The tested soil was montmorillonite (Mt) and polyacrylamide

(PAM) was used as a soil modifier Micro-scale conformational behavior of PAM in a bulk

solution and in the CPN was characterized using dynamic light scattering (DLS) and

spectroscopic ellipsometry (SE) respectively Corresponding meso-scale property changes of the

CPN were characterized by measuring specific surface area swelling potential and permeability

A coarse-grained computer simulation technique dissipative particle dynamics (DPD) was used

to investigate the effects of the micro-scale PAM conformation on the meso-scale CPN properties

An optimized procedure was developed for synthesizing tunable CPN using an expansive

clay (Mt) and a water-soluble responsive polymer (PAM) The optimum condition for the

maximum quantity of intercalated structure formation was found with low molecular weight

nonionic PAM at clay-to-polymer volume ratio 2 and clay content 0001 With the use of a

water-soluble polymer large-scale production of in-situ modifiable engineered clay soils is

feasible

Corresponding to pH-dependent conformation of PAM in a bulk solution PAM in the

synthesized CPN also had pH-dependent conformation to lesser degree due to the presence of

surfaces Layer thickness of PAM adsorbed on a surface specific surface area and swelling

potential increased with increasing pH corresponding to extended PAM conformation at basic

pH The increase in the swelling potential resulted in pore size reduction leading to a decrease in

permeability

106

With the use of DPD technique a quantitative linkage between PAM conformation and a

CPN property ndash interlayer spacing ndash was made for a system containing one PAM molecule

sandwiched between two Mt layers Although it is still challenging to quantitatively link

computational findings to meso-scale experimental results computer simulation was

demonstrated to be a viable tool providing good qualitative agreement with experimental

findings In addition computer simulation provided the insight to overcome experimental

limitations On the other hand experimental results provided information that computer

simulation did not capture such as pH-dependent behavior of Mt and hydrolysis behavior of PAM

at neutral pH

This study indicates that the use of pH-responsive polymer is a viable tool for soil

modification The conformation of a pH-responsive polymer varies with ambient solution pH

leading to system property changes due to changes in soil fabric ie interlayer and interparticle

spacings Thus this study may offer a new outlook for a purpose of creating engineered soil

systems A responsive polymer can be widely utilized in the fields of geotechnical and

geoenvironmental engineering to build an engineered soil system which has tunable system

properties

107

Future Work

Strength and Deformation of Clay-Polymer Nanocomposites

Since geotechnical applications typically include supporting the load imposed by

buildings or structures mechanical properties such as shear strength compressive strength and

deformation are of interest Polymer introduction may affect mechanical properties of the

system thus effects of polymer are required to be investigated by means of laboratory testing

used in the field of geotechnical engineering

Polymer molecules provide additional bonding between clay particles or between clay

layers thus better mechanical properties may be obtained Polymer molecules are typically

flexible while clay particles are relatively rigid and hence better toughness may be expected for

clay-polymer systems Thus mechanical properties for polymer-treated clay soil systems will be

investigated by means of geotechnical testing such as direct shear test consolidation test and

triaxial tests Variables such as sample type molecular weight and ionic type of polymer and

ionic strength can be used to explore effects of each variable If current experimental techniques

are not suitable for the new material to investigate such an effect of interest a new technique can

be developed considering both characteristics of clays and polymers

Geoenvironmental Applications of Clay-Polymer Nanocomposites

In contrast to the geotechnical applications chemistry and biology are important in the

field of geoenvironmental engineering When clay-polymer composites are applied in field

interactions of the composites with preexisting ions and microorganisms may be of concern since

such interactions may affect the clay-polymer system

For example as found in this study a clay-polymer system can have lower permeability

than pure clay systems Thus it can be used for an environmental barrier or filter that prevents

108

contaminants from exposure to nature However preexisting cations andor microorganisms can

neutralize negatively charged groups of polyacrylamide leading to an increase in permeability

Preexisting cations andor microorganisms can also provide additional adsorption sites for

contaminants improving the barrier properties of the system Therefore such factors need to be

investigated prior to introducing polymers into clay soil systems Laboratory testing including

adsorption test for contaminants on the clay-polymer composites can be performed in the

presence of different ions andor microorganisms to explore effects of each factor on the barrier

property of the clay-polymer composites

Expansion of the Use of Computer Simulation for Investigation of Clay-Polymer Nanocomposites

With current experimental technologies it is very challenging to characterize clay-

polymer nanocomposites since it is a very small complex system As shown in this study

dissipative particle dynamics is a viable tool to characterize such a small complex system Thus

the technique can be used to explore unknown or controversial issues of clay-polymer systems

since computer simulation has the advantage of isolating a factor of interest

For example the most dominant factor in the behavior of the ldquotunablerdquo clay polymer

nanocomposites and complex pH-dependencies observed in specific surface area measurement

can be demonstrated with the use of computer simulation techniques Each factor affecting the

behavior can be isolated during simulation to find degree of influence Comparing the found

degree of influence the most dominant factor(s) can be determined

109

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119

Rotenberg B Marry V Vuilleumier R Malikova N Simon C and Turq P 2007 Water

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Santamarina J C Klein K A Palomino A and Guimaraes M S 2002a Micro-Scale

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120

Shen Z Simon G P and Cheng Y-B 2002a Comparison of solution intercalation and melt

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Shen Z Simon G P and Cheng Y-B 2002b Effects of molecular weight and clay organo-

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2815-2819

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Tran N H Dennis G R Milev A S Kannangara G S K Wilson M A and Lamb R N

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122

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Wu S and Shanks R A 2004 Solubility study of polyacrylamide in polar solvents Journal of


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Zeng Q H Yu A B and Lu G Q 2008 Multiscale modeling and simulation of polymer

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5(10) 1574-1592

Zysset M and Schindler P W 1996 The proton promoted dissolution kinetics of K-

montmorillonite Geochimica et Cosmochimica Acta 60(6) 921-931

123

APPENDIX A EXAMPLE CALCULATION FOR CLAY-TO-

POLYMER VOLUME RATIO

If we have 25g montmorillonite (ρ=25g0cm3) and 375g polyacrylamide (ρ=075g0cm3)

3

310

52

25cm

cmg

gV onitemontmorill

3

35

750

753cm

cmg

gV midepolyacryla

Thus clay-to-polymer volume ratio will be equal to 2

When clay-polymer nanocomposites are prepared using above amount of clay and polymer to set

clay content to 001 total volume of water to be used will be

mlcmg

g

contentclay

Mass

Vclay

clay

water 1000010

52

253

124

APPENDIX B PRESSURIZED PERMEABILITY

Sample Calculation

Measured flow rate Q = 10-5 cm3s = 61 x 10-7 in3s

Dynamic viscosity of water μ = 129 x 10-7 lbsin2 at 25degC

Sample diameter D = 1 in

Specimen length L = 15 in

Applied inlet pressure (driving pressure) Pa = 50 lbin2

Applied outlet pressure (atmospheric pressure) Pb = 147 lbin2

Unit weight of water γw = 624 lbft3 = 00361 lbin3

Cross-sectional area of the sample A = πD24 = 0785 in2

Hydraulic head due to the inlet pressure ha = Paγw = 138462 in

Hydraulic head due to the outlet pressure hb = Paγw = 40678 in

From Darcyrsquos law

L

hhAkQ ab )(

Thus hydraulic conductivity (permeability) k will be

)( ba hhA

LQk

= 1193 x 10-9 ins = 3029 x 10-9 cms

125

APPENDIX C DPD EQUILIBRATION

Figure C1 shows ltRg2gt12 of the simulated polymer sandwiched between two clay

surfaces as a function of pH at clay-to-polymer volume ratio 4 This confirms that each condition

in Figure 55 reached equilibrium at time step 500000

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(a) (b)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(c) (d)

126

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(e) (f)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

(g) (h)


0143 (d) 02 (e) 025 (f) 033 (g) 05 and (h) 08 at clay-to-polymer volume ratio 4

127

APPENDIX D SCALING OF SIMULATED SYSTEM

As described in Section 52 one simulation length unit represents 4481 Aring From this

relationship the length of a polymer molecule composed of 236 beads with cutoff radius 2289 is

242 nm This represents a PAM molecule with molecular weight asymp 80000 gmol Similarly the

simulated surface composed of 22 beads times 22 beads represents a Mt surface with dimensions

of 225 nm x 225 nm Figure D1 shows a coarse-grained DPD bead a simulated PAM molecule

and a simulated Mt surface used in this study Figure D2 shows an example of unit conversion

between simulated values and real values

(a) (b) (c)


molecule and (c) a Mt surface

0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

paci

ng

pH

0

5

10

15

20

5 7 9 11 13

Inte

rlay

er S

paci

ng (

nm)

pH

(a) (b)


real unit (nm)

103 nm MW asymp 80000 gmol 225 nm

225 nm

128

VITA

Sungho Kim

EDUCATION PhD Civil and Environmental Engineering The Pennsylvania State University Dec 2011 Dissertation ldquoAn Engineered Clay Soil System Using Functional Polymersrdquo MSCE Civil and Environmental Engineering The Pennsylvania State University Aug 2008 Thesis ldquoPolyacrylamide-Treated Kaolin Clay A Fabric Studyrdquo BSE Environmental Science and Engineering (dual degree in Civil Engineering) Korea University Feb 2005

EXPERIENCE HIGHLIGHTS Graduate Research Assistant Aug 2006 ndash Dec 2011 Soil Particle Modification for the Development of Engineered Soil Materials

Polymer-Treated Clay Soils Engineered Soil Fabrics - Pore Fluid Chemistry and Mineral Mixtures Clay Particle Surface Modification Micro-Scale Soil Mechanics Multi-Scale Computer Simulation from Atomistic to Meso (MC MD DPD) NSF Research Project Jul 2010 ndash Dec 2011 PI Angelica M Palomino Project name Engineering a Modifiable clay ldquoTunablerdquo Polymer-Clay Composite Award number 1041995 Sponsor National Science Foundation Division of Civil Mechanical and Manufacturing

Innovation USA Undergraduate Research Assistant 2004 Project name Nonstructural Strategies for flood prevention Supervisor Ministry of Construction amp Transportation South Korea

(Since 2009 Ministry of Land Transport and Maritime Affairs) Republic of Korea Air Force Jan 1999 ndash Jul 2001 Detection Radar Operator Airman First Class

AWARDS AND FELLOWSHIPS Graduate Research Assistantship 2006 ndash 2011 Student Grant of the Clay Minerals Society 2011 Graduate Scholarship of the Construction Material Testing Laboratory 2009 2008 Undergraduate Research Assistantship 2004 Honors Scholarship 2004 2003 2002 Semester High Honor 2004 2003 2002

ii

The dissertation of Sungho Kim was reviewed and approved by the following

Angelica Maria Palomino

Assistant Professor of Civil and Environmental Engineering

Dissertation Advisor

Chair of Committee

Mian C Wang

Professor Emeritus of Civil and Environmental Engineering

James H Adair

Professor of Material Science and Engineering

Coray M Colina

Associate Professor of Material Science and Engineering

Peggy A Johnson

Professor of Civil and Environmental Engineering

Head of the Department of Civil and Environmental Engineering

Signatures are on file in the Graduate School

iii

ABSTRACT























iv








v

TABLE OF CONTENTS


LIST OF TABLES xi


INTRODUCTION 1

11 Motivation 3

12 Objectives 4

13 Hypothesis 5


LITERATURE REVIEW 7









261 Overview 25



31 Introduction 32


321 Materials 33




vi






34 Conclusions 49


41 Introduction 51

42 Materials 53












46 Conclusions 82


51 Introduction 84






vii

57 Conclusions 103

CONCLUSIONS 105

Future Work 107

REFERENCES 109





VITA 128

viii

LIST OF FIGURES

































ix







48










pH = 3 6 and 115 63






cell 75











pH 90

x

























real unit (nm) 127

xi

LIST OF TABLES











xii

ACKNOWLEDGEMENTS
























Chapter 1

INTRODUCTION



















1992)




2


























3












11 Motivation



polymer composites







4

12 Objectives

























5




13 Hypothesis



















6



7

Chapter 2

LITERATURE REVIEW






















1999)

8

























9








Si

O

Al

Mg

Na

basal

spacing

096 nm

to ~ infin

Octahedral

sheet

Tetrahedral

sheet

Interlayer

space

Tetrahedral

sheet

10


























11






(2)

(3)

(1)

Surface potential


ζ (zeta potential)






shear

plane

Stern

layer


12



2

0

2

0

2

1

zc

T

Ne

k

av

B






















13


























14
























15










Heimann 1993)
















16

a

CH

NH2

O = C

CH2















+ bNaOH rarr + bNH3



CH2

a-b

CH

NH2

O = C

CH2

b

CH

Na+

O = C

O-

17

a

CH

NH2

O = C

CH2 CH2

b

CH

N+

O = C

O

(CH2)2

(CH3)3

Cl-

+ OH- rarr +




















CH2

n-m

CH

NH2

O = C

CH2

m

CH

Na+

O = C

O- n-m

CH2 CH2

OH N+

(CH3)3 Cl-

18
















Contracted coiled


Partially coiled



at pH gt 105


19


























20


























21



















(a) (b) (c)



22
























23


























24

























25









)exp()tan( i

||

||)tan(

s

p

r

r

sp








261 Overview




26












Quantum




Molecular

Mechanics(atoms)

Chara

cte

ristic

Length

Characteristic Time

mm

μm

nm

pico

seconds

nano

seconds

micro


FEM DEM

(finite elements)



27

























28

L AL

A

(a) (b)

















29




ijF = ijCF + ij

DF + ijRF

ijCF =

cij

cij

ij

ij

c

ij

ij

rrif

rrifr

r

r

ra

0

))(1(

ijDF = -γij∙ω

Dmiddotrijmiddotij

ij

ij

ij

ij

r

rv

r

r )(


Rmiddotrij

ij

ijij

r

r

t








ωD(r) = [ωR(r)]2

σ2 = 2γkBT



c

c

cRD

rrif

rrifr

r

rr

0

)1()]([)(

2

2

30




2























31






32

Chapter 3









31 Introduction















33


polymer



















321 Materials

3211 Bentonite



34






















35


component component

SiO2 6302

Al2O3 2108

Fe2O3 325

FeO 035

CaO 065

MgO 267

Na2O 257

trace 072

LOI 564






Ltd)











(cmolkg) 808


Giese 2001)




(gmol) a

High molecular

weight N300

~ 6 x 106

Low molecular



n

CH

NH2

O = C

CH2

36


























37



125 2 4 8 125 25 and 625























38














7˚)











39





Livermore CA)




















40


Sample

numbera

Clay

content

Polymer

type

pH of

polymer

solution

Clay-to-

polymer

volume ratio

Basal spacing

(nm)b

XRD intensity

at peak

(counts)

N1 0001 na na na

1227 150

N2 001 1166 160

CC1 0001 nPAM 109 8 1526 225

CC4 0005 nPAM 109 8 1509 280

CC7 001 nPAM 1094 8 1515 200

CC10 003 nPAM 111 8 1215 210

MW1 001 nPAM 1094 125 1527 1211 180 180

MW4 001 NPAM 1096 125 1558 1151 130 115

PH1 001 nPAM 41 8 1515 1289 230 180

PH4 001 nPAM 565 8 1515 1308 210 175

PH7 001 nPAM 1094 8 1515 200

CP1 0001 nPAM 109 125 1557 310

CP4 0001 nPAM 11 2 1541 460

CP7 0001 nPAM 1104 4 1504 400

CP10 001 nPAM 111 8 1515 1289 230 180

CP13 001 nPAM 1094 125 1527 1211 180 180

CP16 001 nPAM 109 25 1108 310



tabulated










41

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1479nm1278nm

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1495nm1192nm

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1494nm1253nm









(a)

(b)

(c)

42

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1527nm1211nm

21plusmn2˚C

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1509nm

1005nm

110˚C

(a)

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1558nm1151nm

21plusmn2˚C

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1511nm

1005nm

110˚C

(b)



43




drying stages
















44





(c)

(b)

(a)

(f)

(e)

(d)

-935

-1062

3917

58737

45

2 7 12 17 22 27

Rel

ativ

e In

ten

sity

2θ˚ (CuKα)

15 nm








(a)

(b)

(c)

M M

M M

M M

46

0

100

200

300

400

500

0001 001 01

Inte

nsi

ty (

cou

nts

)

Clay content

















47


























48

0

100

200

300

400

500

1 10 100

Inte

nsi

ty (

coun

ts)
















49



34 Conclusions












consumption










50










51

Chapter 4


NANOCOMPOSITES







41 Introduction














52


























53

42 Materials

421 Clay Minerals
























54


Palomino 2009)


constituent

constituent

Kaolinite

(Supplier Data)


(Murray 1991)

Bentonite

(Supplier Data)

SiO2 456 463 6302

Al2O3 384 398 2108

Fe2O3 04 325

FeO 035

TiO2 15

CaO 006 065

MgO trace 267

K2O 018

Na2O trace 257

trace 072

LOI 1382 139 564









c Supplier data




55

422 Polyacrylamide
















charged units

Molecular

weight (gmol) a

NPAM N300

None ~ 6 x 106


CPAM C494

20)(

ba

b ~ 4 x 106


a

CH

NH2

O = C

CH2

a

CH

NH2

O = C

CH2 CH2

b

CH

N+

O = C

O

(CH2)2

(CH3)3

Cl-

56




















57

(a) (b)



(a) (b)








3 μm 25 μm

5 μm 10 μm

58





















Dn 2

0

))2

sin(4

(



59


constant D

Dt

Tkd B

)(3











10

100

1000

1 3 5 7 9 11 13

Hy

dro

dy

nam

ic R

adiu

s (

nm

)

pH

Mt

nPAM


60


















conformation of CPN






61


solution pH
























62

Detector

Polarizer

Analyzer

Simulated Surface

Polymer

Layer

Thickness



Light




by water (H2O)















63










225

275

325

375

425

0 400 800 1200

Th

ick

nes

s (

Aring)

Time (minutes)

pH asymp 6

pH asymp 3

pH asymp 115

-30

-20

-10

0

10

20

30

0 400 800 1200

Th

ick

nes

s C

han

ge

Δd

d0

()

Time (minutes)

pH asymp 6

pH asymp 3

pH asymp 115

Δd = d - d0

(a) (b)


pH = 3 6 and 115

64










measurement time
















65

























66
























67
















1985)










68

10

20

30

40

50

1 3 5 7 9 11 13

Surf

ace

area

(m

2g

)

pH

Kaolinite

Kaolinite+nPAM

(a)

400

600

800

1000

1200

1 3 5 7 9 11 13

Surf

ace

area

(m

2g

)

pH

Mt+nPAM

Mt

(b)



69



















polymer

442 Swelling Test





70























71

0

1

2

0 24 48 72

Sw

elli

ng r

ati

o

Time (hour)

pH 115

pH 6

pH 3

(a)

0

5

10

15

0 24 48 72

Sw

elli

ng r

ati

o

Time (hour)

pH 115

pH 6

pH 3

(b)



Untreated

Kaolinite

Untreated

Mt

72













and the CPN













73























study

74










ndash were used
















75

Pressure

Control PanelGas

Supply

Influent

Solution Reservoir

Driving Pressure

Confining


Cell

Effluent

Collector


cell















76



10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bil

ity

(cm

s)

pH

Kaolinite+nPAM

Kaolinite+NPAM

Kaolinite+CPAM

Kaolinite

(a)

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bil

ity

(cm

s)

pH

Kaolinite+nPAM

Kaolinite+NPAM

Kaolinite+CPAM

Kaolinite

(b)


and (b) powder-form

77


























78

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bilit

y (

cms

)

pH

Mt+nPAM

Mt+NPAM

Mt+CPAM

Mt

(a)

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bilit

y (

cms

)

pH

Mt+nPAM

Mt+NPAM

Mt+CPAM

Mt

(b)




79

























80














0

10

20

30

40

0

20

40

60

80

100

1 3 5 7 9 11 13

Ad

sorb

ed P

AM

Lay

er T

hic

kn

ess

(nm

)

Hy

dro

dy

nam

ic R

adiu

s (n

m)

Solution pH






81

0

5

10

15

0

10

20

30

40

1 3 5 7 9 11 13

Sw

elling

R

atio

Ad

sorb

ed P

AM

Lay

er T

hic

knes

s (n

m)

Solution pH


Swelling ratio
















82













46 Conclusions












83











84

Chapter 5

COMPUTER SIMULATION








51 Introduction










work





85

























86
















Mass m m





Energy unit ε ε

Time unit τ 1d τ


87


























88


= 1 = 12

Mass 1 12

Mass density 3 3



γ 45 23587

σ 3 23792

ε 1 12

τ 1 2289


water

Non-

charged

PAM

Charged

PAM

Non-

charged

clay

Charged

Clay Counterion

water 13104 13261 10483 13261 4717 13104

Non-charged

PAM 13104 13104 4717 1048 13261

Charged PAM 13104 1048 13261 13261

Non-charged

clay 13104 13104 13261


Counterion 13104


1998)


89



















i

cmiig rrmM

R 2212)(

1





Spitnik 1947)

90

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

3

4

5

5 7 9 11 13

ltR

g2gt

12

pH

(b)


pH

91

apKc

cpH

)

1(log10














35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

(a) (b)


92












(Mt) surface














93

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Poly

mer

Lay

er T

hic

knes

s

pH

(b)



94

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)





95
























96

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

pac

ing

pH

(b)





97












(Figure 56-h)

98

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)






99

















100

1

2

3

4

5

6

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

pac

ing

pH

(b)



101























102

0

10

20

30

40

50

0

5

10

15

1 3 5 7 9 11 13

Sim

ula

ted

Inte

rlay

er

Spac

ing

Sw

elling R

atio

Solution pH

Swelling ratio

















103







57 Conclusions














scale CPN behaviors




104




pH

105

Chapter 6

CONCLUSIONS
















feasible






permeability

106









at neutral pH







properties

107

Future Work























108




















109

REFERENCES





Lafayette Louisiana



Reports 28(1-2) 1-63





Mater 4(6) 1395-1403



Minerals 50(5) 546-552





















158 235-243


Minerals 34(2) 259-273






110





































293-302












111























2328



143-239



NY 125-129















147(1-2) 35-44





Aspects 281(1-3) 82-91

112




York









New York








8593


253-287









5530

















Polymer 20(8) 969-975

113



214102-8







225-246








Science 138 107-147






1-41



34(15) 5267-5274










Physics 125(22)






16(19) 7493-7502



11265-11277



725-736

114



4435















Physics 115(7) 3322-3329
















304-342


Oxford New York












19(1) 84-90

115


Films 233(1-2) 96-111


San Diego















Science 45(4) 270-279



498

















453-551



8(4) 373-468




4(2) 105-123



116



ISS) 1359-1372


162(11) 826-832















15(2) 193-197











1391


Minerals 47(2) 174-180




1399-1407












Chemistry 46(7) 1485-1490

117





693-713



















77(3) 463-466



Science 108(1) 243-248





20(24) 10382-10388


New York London





10(12) 4554-4559










118










160



265(10) 889-896










184101-7


















New York









119















Chemistry C 111(35) 13170-13176









York












Arbor MI 12-49







159(2-3) 491-501



Equilibria 261(1-2) 366-374




120












Minerals 43(3) 285-293



2815-2819

































Chemistry C 111(23) 8248-8259

121




Nature 346 345-347


Rev 74(3) 385-400




Technology B 22(6) 3450-3453


23(5) 715-724


Field Science 218(4571) 467-469




782-789




York


Minerals 30(1) 1-10









282



Physics 121(5) 2367-2375




20954-20964



Materials 5(12) 1694-1696






122






474




38(4) 343-350









3129








Materials 18(4) 432-436





13-20




1231-1253





5(10) 1574-1592



123




3

310

52

25cm

cmg

gV onitemontmorill

3

35

750

753cm

cmg

gV midepolyacryla




mlcmg

g

contentclay

Mass

Vclay

clay

water 1000010

52

253

124


Sample Calculation












L

hhAkQ ab )(


)( ba hhA

LQk

= 1193 x 10-9 ins = 3029 x 10-9 cms

125





3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(a) (b)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(c) (d)

126

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(e) (f)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

(g) (h)



127









(a) (b) (c)



0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

paci

ng

pH

0

5

10

15

20

5 7 9 11 13

Inte

rlay

er S

paci

ng (

nm)

pH

(a) (b)


real unit (nm)


225 nm

128

VITA

Sungho Kim







iii

ABSTRACT























iv








v

TABLE OF CONTENTS


LIST OF TABLES xi


INTRODUCTION 1

11 Motivation 3

12 Objectives 4

13 Hypothesis 5


LITERATURE REVIEW 7









261 Overview 25



31 Introduction 32


321 Materials 33




vi






34 Conclusions 49


41 Introduction 51

42 Materials 53












46 Conclusions 82


51 Introduction 84






vii

57 Conclusions 103

CONCLUSIONS 105

Future Work 107

REFERENCES 109





VITA 128

viii

LIST OF FIGURES

































ix







48










pH = 3 6 and 115 63






cell 75











pH 90

x

























real unit (nm) 127

xi

LIST OF TABLES











xii

ACKNOWLEDGEMENTS
























Chapter 1

INTRODUCTION



















1992)




2


























3












11 Motivation



polymer composites







4

12 Objectives

























5




13 Hypothesis



















6



7

Chapter 2

LITERATURE REVIEW






















1999)

8

























9








Si

O

Al

Mg

Na

basal

spacing

096 nm

to ~ infin

Octahedral

sheet

Tetrahedral

sheet

Interlayer

space

Tetrahedral

sheet

10


























11






(2)

(3)

(1)

Surface potential


ζ (zeta potential)






shear

plane

Stern

layer


12



2

0

2

0

2

1

zc

T

Ne

k

av

B






















13


























14
























15










Heimann 1993)
















16

a

CH

NH2

O = C

CH2















+ bNaOH rarr + bNH3



CH2

a-b

CH

NH2

O = C

CH2

b

CH

Na+

O = C

O-

17

a

CH

NH2

O = C

CH2 CH2

b

CH

N+

O = C

O

(CH2)2

(CH3)3

Cl-

+ OH- rarr +




















CH2

n-m

CH

NH2

O = C

CH2

m

CH

Na+

O = C

O- n-m

CH2 CH2

OH N+

(CH3)3 Cl-

18
















Contracted coiled


Partially coiled



at pH gt 105


19


























20


























21



















(a) (b) (c)



22
























23


























24

























25









)exp()tan( i

||

||)tan(

s

p

r

r

sp








261 Overview




26












Quantum




Molecular

Mechanics(atoms)

Chara

cte

ristic

Length

Characteristic Time

mm

μm

nm

pico

seconds

nano

seconds

micro


FEM DEM

(finite elements)



27

























28

L AL

A

(a) (b)

















29




ijF = ijCF + ij

DF + ijRF

ijCF =

cij

cij

ij

ij

c

ij

ij

rrif

rrifr

r

r

ra

0

))(1(

ijDF = -γij∙ω

Dmiddotrijmiddotij

ij

ij

ij

ij

r

rv

r

r )(


Rmiddotrij

ij

ijij

r

r

t








ωD(r) = [ωR(r)]2

σ2 = 2γkBT



c

c

cRD

rrif

rrifr

r

rr

0

)1()]([)(

2

2

30




2























31






32

Chapter 3









31 Introduction















33


polymer



















321 Materials

3211 Bentonite



34






















35


component component

SiO2 6302

Al2O3 2108

Fe2O3 325

FeO 035

CaO 065

MgO 267

Na2O 257

trace 072

LOI 564






Ltd)











(cmolkg) 808


Giese 2001)




(gmol) a

High molecular

weight N300

~ 6 x 106

Low molecular



n

CH

NH2

O = C

CH2

36


























37



125 2 4 8 125 25 and 625























38














7˚)











39





Livermore CA)




















40


Sample

numbera

Clay

content

Polymer

type

pH of

polymer

solution

Clay-to-

polymer

volume ratio

Basal spacing

(nm)b

XRD intensity

at peak

(counts)

N1 0001 na na na

1227 150

N2 001 1166 160

CC1 0001 nPAM 109 8 1526 225

CC4 0005 nPAM 109 8 1509 280

CC7 001 nPAM 1094 8 1515 200

CC10 003 nPAM 111 8 1215 210

MW1 001 nPAM 1094 125 1527 1211 180 180

MW4 001 NPAM 1096 125 1558 1151 130 115

PH1 001 nPAM 41 8 1515 1289 230 180

PH4 001 nPAM 565 8 1515 1308 210 175

PH7 001 nPAM 1094 8 1515 200

CP1 0001 nPAM 109 125 1557 310

CP4 0001 nPAM 11 2 1541 460

CP7 0001 nPAM 1104 4 1504 400

CP10 001 nPAM 111 8 1515 1289 230 180

CP13 001 nPAM 1094 125 1527 1211 180 180

CP16 001 nPAM 109 25 1108 310



tabulated










41

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1479nm1278nm

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1495nm1192nm

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1494nm1253nm









(a)

(b)

(c)

42

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1527nm1211nm

21plusmn2˚C

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1509nm

1005nm

110˚C

(a)

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1558nm1151nm

21plusmn2˚C

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1511nm

1005nm

110˚C

(b)



43




drying stages
















44





(c)

(b)

(a)

(f)

(e)

(d)

-935

-1062

3917

58737

45

2 7 12 17 22 27

Rel

ativ

e In

ten

sity

2θ˚ (CuKα)

15 nm








(a)

(b)

(c)

M M

M M

M M

46

0

100

200

300

400

500

0001 001 01

Inte

nsi

ty (

cou

nts

)

Clay content

















47


























48

0

100

200

300

400

500

1 10 100

Inte

nsi

ty (

coun

ts)
















49



34 Conclusions












consumption










50










51

Chapter 4


NANOCOMPOSITES







41 Introduction














52


























53

42 Materials

421 Clay Minerals
























54


Palomino 2009)


constituent

constituent

Kaolinite

(Supplier Data)


(Murray 1991)

Bentonite

(Supplier Data)

SiO2 456 463 6302

Al2O3 384 398 2108

Fe2O3 04 325

FeO 035

TiO2 15

CaO 006 065

MgO trace 267

K2O 018

Na2O trace 257

trace 072

LOI 1382 139 564









c Supplier data




55

422 Polyacrylamide
















charged units

Molecular

weight (gmol) a

NPAM N300

None ~ 6 x 106


CPAM C494

20)(

ba

b ~ 4 x 106


a

CH

NH2

O = C

CH2

a

CH

NH2

O = C

CH2 CH2

b

CH

N+

O = C

O

(CH2)2

(CH3)3

Cl-

56




















57

(a) (b)



(a) (b)








3 μm 25 μm

5 μm 10 μm

58





















Dn 2

0

))2

sin(4

(



59


constant D

Dt

Tkd B

)(3











10

100

1000

1 3 5 7 9 11 13

Hy

dro

dy

nam

ic R

adiu

s (

nm

)

pH

Mt

nPAM


60


















conformation of CPN






61


solution pH
























62

Detector

Polarizer

Analyzer

Simulated Surface

Polymer

Layer

Thickness



Light




by water (H2O)















63










225

275

325

375

425

0 400 800 1200

Th

ick

nes

s (

Aring)

Time (minutes)

pH asymp 6

pH asymp 3

pH asymp 115

-30

-20

-10

0

10

20

30

0 400 800 1200

Th

ick

nes

s C

han

ge

Δd

d0

()

Time (minutes)

pH asymp 6

pH asymp 3

pH asymp 115

Δd = d - d0

(a) (b)


pH = 3 6 and 115

64










measurement time
















65

























66
























67
















1985)










68

10

20

30

40

50

1 3 5 7 9 11 13

Surf

ace

area

(m

2g

)

pH

Kaolinite

Kaolinite+nPAM

(a)

400

600

800

1000

1200

1 3 5 7 9 11 13

Surf

ace

area

(m

2g

)

pH

Mt+nPAM

Mt

(b)



69



















polymer

442 Swelling Test





70























71

0

1

2

0 24 48 72

Sw

elli

ng r

ati

o

Time (hour)

pH 115

pH 6

pH 3

(a)

0

5

10

15

0 24 48 72

Sw

elli

ng r

ati

o

Time (hour)

pH 115

pH 6

pH 3

(b)



Untreated

Kaolinite

Untreated

Mt

72













and the CPN













73























study

74










ndash were used
















75

Pressure

Control PanelGas

Supply

Influent

Solution Reservoir

Driving Pressure

Confining


Cell

Effluent

Collector


cell















76



10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bil

ity

(cm

s)

pH

Kaolinite+nPAM

Kaolinite+NPAM

Kaolinite+CPAM

Kaolinite

(a)

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bil

ity

(cm

s)

pH

Kaolinite+nPAM

Kaolinite+NPAM

Kaolinite+CPAM

Kaolinite

(b)


and (b) powder-form

77


























78

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bilit

y (

cms

)

pH

Mt+nPAM

Mt+NPAM

Mt+CPAM

Mt

(a)

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bilit

y (

cms

)

pH

Mt+nPAM

Mt+NPAM

Mt+CPAM

Mt

(b)




79

























80














0

10

20

30

40

0

20

40

60

80

100

1 3 5 7 9 11 13

Ad

sorb

ed P

AM

Lay

er T

hic

kn

ess

(nm

)

Hy

dro

dy

nam

ic R

adiu

s (n

m)

Solution pH






81

0

5

10

15

0

10

20

30

40

1 3 5 7 9 11 13

Sw

elling

R

atio

Ad

sorb

ed P

AM

Lay

er T

hic

knes

s (n

m)

Solution pH


Swelling ratio
















82













46 Conclusions












83











84

Chapter 5

COMPUTER SIMULATION








51 Introduction










work





85

























86
















Mass m m





Energy unit ε ε

Time unit τ 1d τ


87


























88


= 1 = 12

Mass 1 12

Mass density 3 3



γ 45 23587

σ 3 23792

ε 1 12

τ 1 2289


water

Non-

charged

PAM

Charged

PAM

Non-

charged

clay

Charged

Clay Counterion

water 13104 13261 10483 13261 4717 13104

Non-charged

PAM 13104 13104 4717 1048 13261

Charged PAM 13104 1048 13261 13261

Non-charged

clay 13104 13104 13261


Counterion 13104


1998)


89



















i

cmiig rrmM

R 2212)(

1





Spitnik 1947)

90

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

3

4

5

5 7 9 11 13

ltR

g2gt

12

pH

(b)


pH

91

apKc

cpH

)

1(log10














35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

(a) (b)


92












(Mt) surface














93

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Poly

mer

Lay

er T

hic

knes

s

pH

(b)



94

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)





95
























96

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

pac

ing

pH

(b)





97












(Figure 56-h)

98

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)






99

















100

1

2

3

4

5

6

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

pac

ing

pH

(b)



101























102

0

10

20

30

40

50

0

5

10

15

1 3 5 7 9 11 13

Sim

ula

ted

Inte

rlay

er

Spac

ing

Sw

elling R

atio

Solution pH

Swelling ratio

















103







57 Conclusions














scale CPN behaviors




104




pH

105

Chapter 6

CONCLUSIONS
















feasible






permeability

106









at neutral pH







properties

107

Future Work























108




















109

REFERENCES





Lafayette Louisiana



Reports 28(1-2) 1-63





Mater 4(6) 1395-1403



Minerals 50(5) 546-552





















158 235-243


Minerals 34(2) 259-273






110





































293-302












111























2328



143-239



NY 125-129















147(1-2) 35-44





Aspects 281(1-3) 82-91

112




York









New York








8593


253-287









5530

















Polymer 20(8) 969-975

113



214102-8







225-246








Science 138 107-147






1-41



34(15) 5267-5274










Physics 125(22)






16(19) 7493-7502



11265-11277



725-736

114



4435















Physics 115(7) 3322-3329
















304-342


Oxford New York












19(1) 84-90

115


Films 233(1-2) 96-111


San Diego















Science 45(4) 270-279



498

















453-551



8(4) 373-468




4(2) 105-123



116



ISS) 1359-1372


162(11) 826-832















15(2) 193-197











1391


Minerals 47(2) 174-180




1399-1407












Chemistry 46(7) 1485-1490

117





693-713



















77(3) 463-466



Science 108(1) 243-248





20(24) 10382-10388


New York London





10(12) 4554-4559










118










160



265(10) 889-896










184101-7


















New York









119















Chemistry C 111(35) 13170-13176









York












Arbor MI 12-49







159(2-3) 491-501



Equilibria 261(1-2) 366-374




120












Minerals 43(3) 285-293



2815-2819

































Chemistry C 111(23) 8248-8259

121




Nature 346 345-347


Rev 74(3) 385-400




Technology B 22(6) 3450-3453


23(5) 715-724


Field Science 218(4571) 467-469




782-789




York


Minerals 30(1) 1-10









282



Physics 121(5) 2367-2375




20954-20964



Materials 5(12) 1694-1696






122






474




38(4) 343-350









3129








Materials 18(4) 432-436





13-20




1231-1253





5(10) 1574-1592



123




3

310

52

25cm

cmg

gV onitemontmorill

3

35

750

753cm

cmg

gV midepolyacryla




mlcmg

g

contentclay

Mass

Vclay

clay

water 1000010

52

253

124


Sample Calculation












L

hhAkQ ab )(


)( ba hhA

LQk

= 1193 x 10-9 ins = 3029 x 10-9 cms

125





3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(a) (b)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(c) (d)

126

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(e) (f)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

(g) (h)



127









(a) (b) (c)



0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

paci

ng

pH

0

5

10

15

20

5 7 9 11 13

Inte

rlay

er S

paci

ng (

nm)

pH

(a) (b)


real unit (nm)


225 nm

128

VITA

Sungho Kim







iv








v

TABLE OF CONTENTS


LIST OF TABLES xi


INTRODUCTION 1

11 Motivation 3

12 Objectives 4

13 Hypothesis 5


LITERATURE REVIEW 7









261 Overview 25



31 Introduction 32


321 Materials 33




vi






34 Conclusions 49


41 Introduction 51

42 Materials 53












46 Conclusions 82


51 Introduction 84






vii

57 Conclusions 103

CONCLUSIONS 105

Future Work 107

REFERENCES 109





VITA 128

viii

LIST OF FIGURES

































ix







48










pH = 3 6 and 115 63






cell 75











pH 90

x

























real unit (nm) 127

xi

LIST OF TABLES











xii

ACKNOWLEDGEMENTS
























Chapter 1

INTRODUCTION



















1992)




2


























3












11 Motivation



polymer composites







4

12 Objectives

























5




13 Hypothesis



















6



7

Chapter 2

LITERATURE REVIEW






















1999)

8

























9








Si

O

Al

Mg

Na

basal

spacing

096 nm

to ~ infin

Octahedral

sheet

Tetrahedral

sheet

Interlayer

space

Tetrahedral

sheet

10


























11






(2)

(3)

(1)

Surface potential


ζ (zeta potential)






shear

plane

Stern

layer


12



2

0

2

0

2

1

zc

T

Ne

k

av

B






















13


























14
























15










Heimann 1993)
















16

a

CH

NH2

O = C

CH2















+ bNaOH rarr + bNH3



CH2

a-b

CH

NH2

O = C

CH2

b

CH

Na+

O = C

O-

17

a

CH

NH2

O = C

CH2 CH2

b

CH

N+

O = C

O

(CH2)2

(CH3)3

Cl-

+ OH- rarr +




















CH2

n-m

CH

NH2

O = C

CH2

m

CH

Na+

O = C

O- n-m

CH2 CH2

OH N+

(CH3)3 Cl-

18
















Contracted coiled


Partially coiled



at pH gt 105


19


























20


























21



















(a) (b) (c)



22
























23


























24

























25









)exp()tan( i

||

||)tan(

s

p

r

r

sp








261 Overview




26












Quantum




Molecular

Mechanics(atoms)

Chara

cte

ristic

Length

Characteristic Time

mm

μm

nm

pico

seconds

nano

seconds

micro


FEM DEM

(finite elements)



27

























28

L AL

A

(a) (b)

















29




ijF = ijCF + ij

DF + ijRF

ijCF =

cij

cij

ij

ij

c

ij

ij

rrif

rrifr

r

r

ra

0

))(1(

ijDF = -γij∙ω

Dmiddotrijmiddotij

ij

ij

ij

ij

r

rv

r

r )(


Rmiddotrij

ij

ijij

r

r

t








ωD(r) = [ωR(r)]2

σ2 = 2γkBT



c

c

cRD

rrif

rrifr

r

rr

0

)1()]([)(

2

2

30




2























31






32

Chapter 3









31 Introduction















33


polymer



















321 Materials

3211 Bentonite



34






















35


component component

SiO2 6302

Al2O3 2108

Fe2O3 325

FeO 035

CaO 065

MgO 267

Na2O 257

trace 072

LOI 564






Ltd)











(cmolkg) 808


Giese 2001)




(gmol) a

High molecular

weight N300

~ 6 x 106

Low molecular



n

CH

NH2

O = C

CH2

36


























37



125 2 4 8 125 25 and 625























38














7˚)











39





Livermore CA)




















40


Sample

numbera

Clay

content

Polymer

type

pH of

polymer

solution

Clay-to-

polymer

volume ratio

Basal spacing

(nm)b

XRD intensity

at peak

(counts)

N1 0001 na na na

1227 150

N2 001 1166 160

CC1 0001 nPAM 109 8 1526 225

CC4 0005 nPAM 109 8 1509 280

CC7 001 nPAM 1094 8 1515 200

CC10 003 nPAM 111 8 1215 210

MW1 001 nPAM 1094 125 1527 1211 180 180

MW4 001 NPAM 1096 125 1558 1151 130 115

PH1 001 nPAM 41 8 1515 1289 230 180

PH4 001 nPAM 565 8 1515 1308 210 175

PH7 001 nPAM 1094 8 1515 200

CP1 0001 nPAM 109 125 1557 310

CP4 0001 nPAM 11 2 1541 460

CP7 0001 nPAM 1104 4 1504 400

CP10 001 nPAM 111 8 1515 1289 230 180

CP13 001 nPAM 1094 125 1527 1211 180 180

CP16 001 nPAM 109 25 1108 310



tabulated










41

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1479nm1278nm

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1495nm1192nm

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1494nm1253nm









(a)

(b)

(c)

42

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1527nm1211nm

21plusmn2˚C

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1509nm

1005nm

110˚C

(a)

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1558nm1151nm

21plusmn2˚C

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1511nm

1005nm

110˚C

(b)



43




drying stages
















44





(c)

(b)

(a)

(f)

(e)

(d)

-935

-1062

3917

58737

45

2 7 12 17 22 27

Rel

ativ

e In

ten

sity

2θ˚ (CuKα)

15 nm








(a)

(b)

(c)

M M

M M

M M

46

0

100

200

300

400

500

0001 001 01

Inte

nsi

ty (

cou

nts

)

Clay content

















47


























48

0

100

200

300

400

500

1 10 100

Inte

nsi

ty (

coun

ts)
















49



34 Conclusions












consumption










50










51

Chapter 4


NANOCOMPOSITES







41 Introduction














52


























53

42 Materials

421 Clay Minerals
























54


Palomino 2009)


constituent

constituent

Kaolinite

(Supplier Data)


(Murray 1991)

Bentonite

(Supplier Data)

SiO2 456 463 6302

Al2O3 384 398 2108

Fe2O3 04 325

FeO 035

TiO2 15

CaO 006 065

MgO trace 267

K2O 018

Na2O trace 257

trace 072

LOI 1382 139 564









c Supplier data




55

422 Polyacrylamide
















charged units

Molecular

weight (gmol) a

NPAM N300

None ~ 6 x 106


CPAM C494

20)(

ba

b ~ 4 x 106


a

CH

NH2

O = C

CH2

a

CH

NH2

O = C

CH2 CH2

b

CH

N+

O = C

O

(CH2)2

(CH3)3

Cl-

56




















57

(a) (b)



(a) (b)








3 μm 25 μm

5 μm 10 μm

58





















Dn 2

0

))2

sin(4

(



59


constant D

Dt

Tkd B

)(3











10

100

1000

1 3 5 7 9 11 13

Hy

dro

dy

nam

ic R

adiu

s (

nm

)

pH

Mt

nPAM


60


















conformation of CPN






61


solution pH
























62

Detector

Polarizer

Analyzer

Simulated Surface

Polymer

Layer

Thickness



Light




by water (H2O)















63










225

275

325

375

425

0 400 800 1200

Th

ick

nes

s (

Aring)

Time (minutes)

pH asymp 6

pH asymp 3

pH asymp 115

-30

-20

-10

0

10

20

30

0 400 800 1200

Th

ick

nes

s C

han

ge

Δd

d0

()

Time (minutes)

pH asymp 6

pH asymp 3

pH asymp 115

Δd = d - d0

(a) (b)


pH = 3 6 and 115

64










measurement time
















65

























66
























67
















1985)










68

10

20

30

40

50

1 3 5 7 9 11 13

Surf

ace

area

(m

2g

)

pH

Kaolinite

Kaolinite+nPAM

(a)

400

600

800

1000

1200

1 3 5 7 9 11 13

Surf

ace

area

(m

2g

)

pH

Mt+nPAM

Mt

(b)



69



















polymer

442 Swelling Test





70























71

0

1

2

0 24 48 72

Sw

elli

ng r

ati

o

Time (hour)

pH 115

pH 6

pH 3

(a)

0

5

10

15

0 24 48 72

Sw

elli

ng r

ati

o

Time (hour)

pH 115

pH 6

pH 3

(b)



Untreated

Kaolinite

Untreated

Mt

72













and the CPN













73























study

74










ndash were used
















75

Pressure

Control PanelGas

Supply

Influent

Solution Reservoir

Driving Pressure

Confining


Cell

Effluent

Collector


cell















76



10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bil

ity

(cm

s)

pH

Kaolinite+nPAM

Kaolinite+NPAM

Kaolinite+CPAM

Kaolinite

(a)

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bil

ity

(cm

s)

pH

Kaolinite+nPAM

Kaolinite+NPAM

Kaolinite+CPAM

Kaolinite

(b)


and (b) powder-form

77


























78

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bilit

y (

cms

)

pH

Mt+nPAM

Mt+NPAM

Mt+CPAM

Mt

(a)

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bilit

y (

cms

)

pH

Mt+nPAM

Mt+NPAM

Mt+CPAM

Mt

(b)




79

























80














0

10

20

30

40

0

20

40

60

80

100

1 3 5 7 9 11 13

Ad

sorb

ed P

AM

Lay

er T

hic

kn

ess

(nm

)

Hy

dro

dy

nam

ic R

adiu

s (n

m)

Solution pH






81

0

5

10

15

0

10

20

30

40

1 3 5 7 9 11 13

Sw

elling

R

atio

Ad

sorb

ed P

AM

Lay

er T

hic

knes

s (n

m)

Solution pH


Swelling ratio
















82













46 Conclusions












83











84

Chapter 5

COMPUTER SIMULATION








51 Introduction










work





85

























86
















Mass m m





Energy unit ε ε

Time unit τ 1d τ


87


























88


= 1 = 12

Mass 1 12

Mass density 3 3



γ 45 23587

σ 3 23792

ε 1 12

τ 1 2289


water

Non-

charged

PAM

Charged

PAM

Non-

charged

clay

Charged

Clay Counterion

water 13104 13261 10483 13261 4717 13104

Non-charged

PAM 13104 13104 4717 1048 13261

Charged PAM 13104 1048 13261 13261

Non-charged

clay 13104 13104 13261


Counterion 13104


1998)


89



















i

cmiig rrmM

R 2212)(

1





Spitnik 1947)

90

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

3

4

5

5 7 9 11 13

ltR

g2gt

12

pH

(b)


pH

91

apKc

cpH

)

1(log10














35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

(a) (b)


92












(Mt) surface














93

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Poly

mer

Lay

er T

hic

knes

s

pH

(b)



94

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)





95
























96

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

pac

ing

pH

(b)





97












(Figure 56-h)

98

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)






99

















100

1

2

3

4

5

6

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

pac

ing

pH

(b)



101























102

0

10

20

30

40

50

0

5

10

15

1 3 5 7 9 11 13

Sim

ula

ted

Inte

rlay

er

Spac

ing

Sw

elling R

atio

Solution pH

Swelling ratio

















103







57 Conclusions














scale CPN behaviors




104




pH

105

Chapter 6

CONCLUSIONS
















feasible






permeability

106









at neutral pH







properties

107

Future Work























108




















109

REFERENCES





Lafayette Louisiana



Reports 28(1-2) 1-63





Mater 4(6) 1395-1403



Minerals 50(5) 546-552





















158 235-243


Minerals 34(2) 259-273






110





































293-302












111























2328



143-239



NY 125-129















147(1-2) 35-44





Aspects 281(1-3) 82-91

112




York









New York








8593


253-287









5530

















Polymer 20(8) 969-975

113



214102-8







225-246








Science 138 107-147






1-41



34(15) 5267-5274










Physics 125(22)






16(19) 7493-7502



11265-11277



725-736

114



4435















Physics 115(7) 3322-3329
















304-342


Oxford New York












19(1) 84-90

115


Films 233(1-2) 96-111


San Diego















Science 45(4) 270-279



498

















453-551



8(4) 373-468




4(2) 105-123



116



ISS) 1359-1372


162(11) 826-832















15(2) 193-197











1391


Minerals 47(2) 174-180




1399-1407












Chemistry 46(7) 1485-1490

117





693-713



















77(3) 463-466



Science 108(1) 243-248





20(24) 10382-10388


New York London





10(12) 4554-4559










118










160



265(10) 889-896










184101-7


















New York









119















Chemistry C 111(35) 13170-13176









York












Arbor MI 12-49







159(2-3) 491-501



Equilibria 261(1-2) 366-374




120












Minerals 43(3) 285-293



2815-2819

































Chemistry C 111(23) 8248-8259

121




Nature 346 345-347


Rev 74(3) 385-400




Technology B 22(6) 3450-3453


23(5) 715-724


Field Science 218(4571) 467-469




782-789




York


Minerals 30(1) 1-10









282



Physics 121(5) 2367-2375




20954-20964



Materials 5(12) 1694-1696






122






474




38(4) 343-350









3129








Materials 18(4) 432-436





13-20




1231-1253





5(10) 1574-1592



123




3

310

52

25cm

cmg

gV onitemontmorill

3

35

750

753cm

cmg

gV midepolyacryla




mlcmg

g

contentclay

Mass

Vclay

clay

water 1000010

52

253

124


Sample Calculation












L

hhAkQ ab )(


)( ba hhA

LQk

= 1193 x 10-9 ins = 3029 x 10-9 cms

125





3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(a) (b)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(c) (d)

126

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(e) (f)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

(g) (h)



127









(a) (b) (c)



0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

paci

ng

pH

0

5

10

15

20

5 7 9 11 13

Inte

rlay

er S

paci

ng (

nm)

pH

(a) (b)


real unit (nm)


225 nm

128

VITA

Sungho Kim







v

TABLE OF CONTENTS


LIST OF TABLES xi


INTRODUCTION 1

11 Motivation 3

12 Objectives 4

13 Hypothesis 5


LITERATURE REVIEW 7









261 Overview 25



31 Introduction 32


321 Materials 33




vi






34 Conclusions 49


41 Introduction 51

42 Materials 53












46 Conclusions 82


51 Introduction 84






vii

57 Conclusions 103

CONCLUSIONS 105

Future Work 107

REFERENCES 109





VITA 128

viii

LIST OF FIGURES

































ix







48










pH = 3 6 and 115 63






cell 75











pH 90

x

























real unit (nm) 127

xi

LIST OF TABLES











xii

ACKNOWLEDGEMENTS
























Chapter 1

INTRODUCTION



















1992)




2


























3












11 Motivation



polymer composites







4

12 Objectives

























5




13 Hypothesis



















6



7

Chapter 2

LITERATURE REVIEW






















1999)

8

























9








Si

O

Al

Mg

Na

basal

spacing

096 nm

to ~ infin

Octahedral

sheet

Tetrahedral

sheet

Interlayer

space

Tetrahedral

sheet

10


























11






(2)

(3)

(1)

Surface potential


ζ (zeta potential)






shear

plane

Stern

layer


12



2

0

2

0

2

1

zc

T

Ne

k

av

B






















13


























14
























15










Heimann 1993)
















16

a

CH

NH2

O = C

CH2















+ bNaOH rarr + bNH3



CH2

a-b

CH

NH2

O = C

CH2

b

CH

Na+

O = C

O-

17

a

CH

NH2

O = C

CH2 CH2

b

CH

N+

O = C

O

(CH2)2

(CH3)3

Cl-

+ OH- rarr +




















CH2

n-m

CH

NH2

O = C

CH2

m

CH

Na+

O = C

O- n-m

CH2 CH2

OH N+

(CH3)3 Cl-

18
















Contracted coiled


Partially coiled



at pH gt 105


19


























20


























21



















(a) (b) (c)



22
























23


























24

























25









)exp()tan( i

||

||)tan(

s

p

r

r

sp








261 Overview




26












Quantum




Molecular

Mechanics(atoms)

Chara

cte

ristic

Length

Characteristic Time

mm

μm

nm

pico

seconds

nano

seconds

micro


FEM DEM

(finite elements)



27

























28

L AL

A

(a) (b)

















29




ijF = ijCF + ij

DF + ijRF

ijCF =

cij

cij

ij

ij

c

ij

ij

rrif

rrifr

r

r

ra

0

))(1(

ijDF = -γij∙ω

Dmiddotrijmiddotij

ij

ij

ij

ij

r

rv

r

r )(


Rmiddotrij

ij

ijij

r

r

t








ωD(r) = [ωR(r)]2

σ2 = 2γkBT



c

c

cRD

rrif

rrifr

r

rr

0

)1()]([)(

2

2

30




2























31






32

Chapter 3









31 Introduction















33


polymer



















321 Materials

3211 Bentonite



34






















35


component component

SiO2 6302

Al2O3 2108

Fe2O3 325

FeO 035

CaO 065

MgO 267

Na2O 257

trace 072

LOI 564






Ltd)











(cmolkg) 808


Giese 2001)




(gmol) a

High molecular

weight N300

~ 6 x 106

Low molecular



n

CH

NH2

O = C

CH2

36


























37



125 2 4 8 125 25 and 625























38














7˚)











39





Livermore CA)




















40


Sample

numbera

Clay

content

Polymer

type

pH of

polymer

solution

Clay-to-

polymer

volume ratio

Basal spacing

(nm)b

XRD intensity

at peak

(counts)

N1 0001 na na na

1227 150

N2 001 1166 160

CC1 0001 nPAM 109 8 1526 225

CC4 0005 nPAM 109 8 1509 280

CC7 001 nPAM 1094 8 1515 200

CC10 003 nPAM 111 8 1215 210

MW1 001 nPAM 1094 125 1527 1211 180 180

MW4 001 NPAM 1096 125 1558 1151 130 115

PH1 001 nPAM 41 8 1515 1289 230 180

PH4 001 nPAM 565 8 1515 1308 210 175

PH7 001 nPAM 1094 8 1515 200

CP1 0001 nPAM 109 125 1557 310

CP4 0001 nPAM 11 2 1541 460

CP7 0001 nPAM 1104 4 1504 400

CP10 001 nPAM 111 8 1515 1289 230 180

CP13 001 nPAM 1094 125 1527 1211 180 180

CP16 001 nPAM 109 25 1108 310



tabulated










41

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1479nm1278nm

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1495nm1192nm

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1494nm1253nm









(a)

(b)

(c)

42

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1527nm1211nm

21plusmn2˚C

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1509nm

1005nm

110˚C

(a)

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1558nm1151nm

21plusmn2˚C

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1511nm

1005nm

110˚C

(b)



43




drying stages
















44





(c)

(b)

(a)

(f)

(e)

(d)

-935

-1062

3917

58737

45

2 7 12 17 22 27

Rel

ativ

e In

ten

sity

2θ˚ (CuKα)

15 nm








(a)

(b)

(c)

M M

M M

M M

46

0

100

200

300

400

500

0001 001 01

Inte

nsi

ty (

cou

nts

)

Clay content

















47


























48

0

100

200

300

400

500

1 10 100

Inte

nsi

ty (

coun

ts)
















49



34 Conclusions












consumption










50










51

Chapter 4


NANOCOMPOSITES







41 Introduction














52


























53

42 Materials

421 Clay Minerals
























54


Palomino 2009)


constituent

constituent

Kaolinite

(Supplier Data)


(Murray 1991)

Bentonite

(Supplier Data)

SiO2 456 463 6302

Al2O3 384 398 2108

Fe2O3 04 325

FeO 035

TiO2 15

CaO 006 065

MgO trace 267

K2O 018

Na2O trace 257

trace 072

LOI 1382 139 564









c Supplier data




55

422 Polyacrylamide
















charged units

Molecular

weight (gmol) a

NPAM N300

None ~ 6 x 106


CPAM C494

20)(

ba

b ~ 4 x 106


a

CH

NH2

O = C

CH2

a

CH

NH2

O = C

CH2 CH2

b

CH

N+

O = C

O

(CH2)2

(CH3)3

Cl-

56




















57

(a) (b)



(a) (b)








3 μm 25 μm

5 μm 10 μm

58





















Dn 2

0

))2

sin(4

(



59


constant D

Dt

Tkd B

)(3











10

100

1000

1 3 5 7 9 11 13

Hy

dro

dy

nam

ic R

adiu

s (

nm

)

pH

Mt

nPAM


60


















conformation of CPN






61


solution pH
























62

Detector

Polarizer

Analyzer

Simulated Surface

Polymer

Layer

Thickness



Light




by water (H2O)















63










225

275

325

375

425

0 400 800 1200

Th

ick

nes

s (

Aring)

Time (minutes)

pH asymp 6

pH asymp 3

pH asymp 115

-30

-20

-10

0

10

20

30

0 400 800 1200

Th

ick

nes

s C

han

ge

Δd

d0

()

Time (minutes)

pH asymp 6

pH asymp 3

pH asymp 115

Δd = d - d0

(a) (b)


pH = 3 6 and 115

64










measurement time
















65

























66
























67
















1985)










68

10

20

30

40

50

1 3 5 7 9 11 13

Surf

ace

area

(m

2g

)

pH

Kaolinite

Kaolinite+nPAM

(a)

400

600

800

1000

1200

1 3 5 7 9 11 13

Surf

ace

area

(m

2g

)

pH

Mt+nPAM

Mt

(b)



69



















polymer

442 Swelling Test





70























71

0

1

2

0 24 48 72

Sw

elli

ng r

ati

o

Time (hour)

pH 115

pH 6

pH 3

(a)

0

5

10

15

0 24 48 72

Sw

elli

ng r

ati

o

Time (hour)

pH 115

pH 6

pH 3

(b)



Untreated

Kaolinite

Untreated

Mt

72













and the CPN













73























study

74










ndash were used
















75

Pressure

Control PanelGas

Supply

Influent

Solution Reservoir

Driving Pressure

Confining


Cell

Effluent

Collector


cell















76



10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bil

ity

(cm

s)

pH

Kaolinite+nPAM

Kaolinite+NPAM

Kaolinite+CPAM

Kaolinite

(a)

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bil

ity

(cm

s)

pH

Kaolinite+nPAM

Kaolinite+NPAM

Kaolinite+CPAM

Kaolinite

(b)


and (b) powder-form

77


























78

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bilit

y (

cms

)

pH

Mt+nPAM

Mt+NPAM

Mt+CPAM

Mt

(a)

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bilit

y (

cms

)

pH

Mt+nPAM

Mt+NPAM

Mt+CPAM

Mt

(b)




79

























80














0

10

20

30

40

0

20

40

60

80

100

1 3 5 7 9 11 13

Ad

sorb

ed P

AM

Lay

er T

hic

kn

ess

(nm

)

Hy

dro

dy

nam

ic R

adiu

s (n

m)

Solution pH






81

0

5

10

15

0

10

20

30

40

1 3 5 7 9 11 13

Sw

elling

R

atio

Ad

sorb

ed P

AM

Lay

er T

hic

knes

s (n

m)

Solution pH


Swelling ratio
















82













46 Conclusions












83











84

Chapter 5

COMPUTER SIMULATION








51 Introduction










work





85

























86
















Mass m m





Energy unit ε ε

Time unit τ 1d τ


87


























88


= 1 = 12

Mass 1 12

Mass density 3 3



γ 45 23587

σ 3 23792

ε 1 12

τ 1 2289


water

Non-

charged

PAM

Charged

PAM

Non-

charged

clay

Charged

Clay Counterion

water 13104 13261 10483 13261 4717 13104

Non-charged

PAM 13104 13104 4717 1048 13261

Charged PAM 13104 1048 13261 13261

Non-charged

clay 13104 13104 13261


Counterion 13104


1998)


89



















i

cmiig rrmM

R 2212)(

1





Spitnik 1947)

90

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

3

4

5

5 7 9 11 13

ltR

g2gt

12

pH

(b)


pH

91

apKc

cpH

)

1(log10














35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

(a) (b)


92












(Mt) surface














93

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Poly

mer

Lay

er T

hic

knes

s

pH

(b)



94

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)





95
























96

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

pac

ing

pH

(b)





97












(Figure 56-h)

98

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)






99

















100

1

2

3

4

5

6

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

pac

ing

pH

(b)



101























102

0

10

20

30

40

50

0

5

10

15

1 3 5 7 9 11 13

Sim

ula

ted

Inte

rlay

er

Spac

ing

Sw

elling R

atio

Solution pH

Swelling ratio

















103







57 Conclusions














scale CPN behaviors




104




pH

105

Chapter 6

CONCLUSIONS
















feasible






permeability

106









at neutral pH







properties

107

Future Work























108




















109

REFERENCES





Lafayette Louisiana



Reports 28(1-2) 1-63





Mater 4(6) 1395-1403



Minerals 50(5) 546-552





















158 235-243


Minerals 34(2) 259-273






110





































293-302












111























2328



143-239



NY 125-129















147(1-2) 35-44





Aspects 281(1-3) 82-91

112




York









New York








8593


253-287









5530

















Polymer 20(8) 969-975

113



214102-8







225-246








Science 138 107-147






1-41



34(15) 5267-5274










Physics 125(22)






16(19) 7493-7502



11265-11277



725-736

114



4435















Physics 115(7) 3322-3329
















304-342


Oxford New York












19(1) 84-90

115


Films 233(1-2) 96-111


San Diego















Science 45(4) 270-279



498

















453-551



8(4) 373-468




4(2) 105-123



116



ISS) 1359-1372


162(11) 826-832















15(2) 193-197











1391


Minerals 47(2) 174-180




1399-1407












Chemistry 46(7) 1485-1490

117





693-713



















77(3) 463-466



Science 108(1) 243-248





20(24) 10382-10388


New York London





10(12) 4554-4559










118










160



265(10) 889-896










184101-7


















New York









119















Chemistry C 111(35) 13170-13176









York












Arbor MI 12-49







159(2-3) 491-501



Equilibria 261(1-2) 366-374




120












Minerals 43(3) 285-293



2815-2819

































Chemistry C 111(23) 8248-8259

121




Nature 346 345-347


Rev 74(3) 385-400




Technology B 22(6) 3450-3453


23(5) 715-724


Field Science 218(4571) 467-469




782-789




York


Minerals 30(1) 1-10









282



Physics 121(5) 2367-2375




20954-20964



Materials 5(12) 1694-1696






122






474




38(4) 343-350









3129








Materials 18(4) 432-436





13-20




1231-1253





5(10) 1574-1592



123




3

310

52

25cm

cmg

gV onitemontmorill

3

35

750

753cm

cmg

gV midepolyacryla




mlcmg

g

contentclay

Mass

Vclay

clay

water 1000010

52

253

124


Sample Calculation












L

hhAkQ ab )(


)( ba hhA

LQk

= 1193 x 10-9 ins = 3029 x 10-9 cms

125





3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(a) (b)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(c) (d)

126

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(e) (f)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

(g) (h)



127









(a) (b) (c)



0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

paci

ng

pH

0

5

10

15

20

5 7 9 11 13

Inte

rlay

er S

paci

ng (

nm)

pH

(a) (b)


real unit (nm)


225 nm

128

VITA

Sungho Kim







vi






34 Conclusions 49


41 Introduction 51

42 Materials 53












46 Conclusions 82


51 Introduction 84






vii

57 Conclusions 103

CONCLUSIONS 105

Future Work 107

REFERENCES 109





VITA 128

viii

LIST OF FIGURES

































ix







48










pH = 3 6 and 115 63






cell 75











pH 90

x

























real unit (nm) 127

xi

LIST OF TABLES











xii

ACKNOWLEDGEMENTS
























Chapter 1

INTRODUCTION



















1992)




2


























3












11 Motivation



polymer composites







4

12 Objectives

























5




13 Hypothesis



















6



7

Chapter 2

LITERATURE REVIEW






















1999)

8

























9








Si

O

Al

Mg

Na

basal

spacing

096 nm

to ~ infin

Octahedral

sheet

Tetrahedral

sheet

Interlayer

space

Tetrahedral

sheet

10


























11






(2)

(3)

(1)

Surface potential


ζ (zeta potential)






shear

plane

Stern

layer


12



2

0

2

0

2

1

zc

T

Ne

k

av

B






















13


























14
























15










Heimann 1993)
















16

a

CH

NH2

O = C

CH2















+ bNaOH rarr + bNH3



CH2

a-b

CH

NH2

O = C

CH2

b

CH

Na+

O = C

O-

17

a

CH

NH2

O = C

CH2 CH2

b

CH

N+

O = C

O

(CH2)2

(CH3)3

Cl-

+ OH- rarr +




















CH2

n-m

CH

NH2

O = C

CH2

m

CH

Na+

O = C

O- n-m

CH2 CH2

OH N+

(CH3)3 Cl-

18
















Contracted coiled


Partially coiled



at pH gt 105


19


























20


























21



















(a) (b) (c)



22
























23


























24

























25









)exp()tan( i

||

||)tan(

s

p

r

r

sp








261 Overview




26












Quantum




Molecular

Mechanics(atoms)

Chara

cte

ristic

Length

Characteristic Time

mm

μm

nm

pico

seconds

nano

seconds

micro


FEM DEM

(finite elements)



27

























28

L AL

A

(a) (b)

















29




ijF = ijCF + ij

DF + ijRF

ijCF =

cij

cij

ij

ij

c

ij

ij

rrif

rrifr

r

r

ra

0

))(1(

ijDF = -γij∙ω

Dmiddotrijmiddotij

ij

ij

ij

ij

r

rv

r

r )(


Rmiddotrij

ij

ijij

r

r

t








ωD(r) = [ωR(r)]2

σ2 = 2γkBT



c

c

cRD

rrif

rrifr

r

rr

0

)1()]([)(

2

2

30




2























31






32

Chapter 3









31 Introduction















33


polymer



















321 Materials

3211 Bentonite



34






















35


component component

SiO2 6302

Al2O3 2108

Fe2O3 325

FeO 035

CaO 065

MgO 267

Na2O 257

trace 072

LOI 564






Ltd)











(cmolkg) 808


Giese 2001)




(gmol) a

High molecular

weight N300

~ 6 x 106

Low molecular



n

CH

NH2

O = C

CH2

36


























37



125 2 4 8 125 25 and 625























38














7˚)











39





Livermore CA)




















40


Sample

numbera

Clay

content

Polymer

type

pH of

polymer

solution

Clay-to-

polymer

volume ratio

Basal spacing

(nm)b

XRD intensity

at peak

(counts)

N1 0001 na na na

1227 150

N2 001 1166 160

CC1 0001 nPAM 109 8 1526 225

CC4 0005 nPAM 109 8 1509 280

CC7 001 nPAM 1094 8 1515 200

CC10 003 nPAM 111 8 1215 210

MW1 001 nPAM 1094 125 1527 1211 180 180

MW4 001 NPAM 1096 125 1558 1151 130 115

PH1 001 nPAM 41 8 1515 1289 230 180

PH4 001 nPAM 565 8 1515 1308 210 175

PH7 001 nPAM 1094 8 1515 200

CP1 0001 nPAM 109 125 1557 310

CP4 0001 nPAM 11 2 1541 460

CP7 0001 nPAM 1104 4 1504 400

CP10 001 nPAM 111 8 1515 1289 230 180

CP13 001 nPAM 1094 125 1527 1211 180 180

CP16 001 nPAM 109 25 1108 310



tabulated










41

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1479nm1278nm

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1495nm1192nm

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1494nm1253nm









(a)

(b)

(c)

42

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1527nm1211nm

21plusmn2˚C

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1509nm

1005nm

110˚C

(a)

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1558nm1151nm

21plusmn2˚C

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1511nm

1005nm

110˚C

(b)



43




drying stages
















44





(c)

(b)

(a)

(f)

(e)

(d)

-935

-1062

3917

58737

45

2 7 12 17 22 27

Rel

ativ

e In

ten

sity

2θ˚ (CuKα)

15 nm








(a)

(b)

(c)

M M

M M

M M

46

0

100

200

300

400

500

0001 001 01

Inte

nsi

ty (

cou

nts

)

Clay content

















47


























48

0

100

200

300

400

500

1 10 100

Inte

nsi

ty (

coun

ts)
















49



34 Conclusions












consumption










50










51

Chapter 4


NANOCOMPOSITES







41 Introduction














52


























53

42 Materials

421 Clay Minerals
























54


Palomino 2009)


constituent

constituent

Kaolinite

(Supplier Data)


(Murray 1991)

Bentonite

(Supplier Data)

SiO2 456 463 6302

Al2O3 384 398 2108

Fe2O3 04 325

FeO 035

TiO2 15

CaO 006 065

MgO trace 267

K2O 018

Na2O trace 257

trace 072

LOI 1382 139 564









c Supplier data




55

422 Polyacrylamide
















charged units

Molecular

weight (gmol) a

NPAM N300

None ~ 6 x 106


CPAM C494

20)(

ba

b ~ 4 x 106


a

CH

NH2

O = C

CH2

a

CH

NH2

O = C

CH2 CH2

b

CH

N+

O = C

O

(CH2)2

(CH3)3

Cl-

56




















57

(a) (b)



(a) (b)








3 μm 25 μm

5 μm 10 μm

58





















Dn 2

0

))2

sin(4

(



59


constant D

Dt

Tkd B

)(3











10

100

1000

1 3 5 7 9 11 13

Hy

dro

dy

nam

ic R

adiu

s (

nm

)

pH

Mt

nPAM


60


















conformation of CPN






61


solution pH
























62

Detector

Polarizer

Analyzer

Simulated Surface

Polymer

Layer

Thickness



Light




by water (H2O)















63










225

275

325

375

425

0 400 800 1200

Th

ick

nes

s (

Aring)

Time (minutes)

pH asymp 6

pH asymp 3

pH asymp 115

-30

-20

-10

0

10

20

30

0 400 800 1200

Th

ick

nes

s C

han

ge

Δd

d0

()

Time (minutes)

pH asymp 6

pH asymp 3

pH asymp 115

Δd = d - d0

(a) (b)


pH = 3 6 and 115

64










measurement time
















65

























66
























67
















1985)










68

10

20

30

40

50

1 3 5 7 9 11 13

Surf

ace

area

(m

2g

)

pH

Kaolinite

Kaolinite+nPAM

(a)

400

600

800

1000

1200

1 3 5 7 9 11 13

Surf

ace

area

(m

2g

)

pH

Mt+nPAM

Mt

(b)



69



















polymer

442 Swelling Test





70























71

0

1

2

0 24 48 72

Sw

elli

ng r

ati

o

Time (hour)

pH 115

pH 6

pH 3

(a)

0

5

10

15

0 24 48 72

Sw

elli

ng r

ati

o

Time (hour)

pH 115

pH 6

pH 3

(b)



Untreated

Kaolinite

Untreated

Mt

72













and the CPN













73























study

74










ndash were used
















75

Pressure

Control PanelGas

Supply

Influent

Solution Reservoir

Driving Pressure

Confining


Cell

Effluent

Collector


cell















76



10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bil

ity

(cm

s)

pH

Kaolinite+nPAM

Kaolinite+NPAM

Kaolinite+CPAM

Kaolinite

(a)

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bil

ity

(cm

s)

pH

Kaolinite+nPAM

Kaolinite+NPAM

Kaolinite+CPAM

Kaolinite

(b)


and (b) powder-form

77


























78

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bilit

y (

cms

)

pH

Mt+nPAM

Mt+NPAM

Mt+CPAM

Mt

(a)

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bilit

y (

cms

)

pH

Mt+nPAM

Mt+NPAM

Mt+CPAM

Mt

(b)




79

























80














0

10

20

30

40

0

20

40

60

80

100

1 3 5 7 9 11 13

Ad

sorb

ed P

AM

Lay

er T

hic

kn

ess

(nm

)

Hy

dro

dy

nam

ic R

adiu

s (n

m)

Solution pH






81

0

5

10

15

0

10

20

30

40

1 3 5 7 9 11 13

Sw

elling

R

atio

Ad

sorb

ed P

AM

Lay

er T

hic

knes

s (n

m)

Solution pH


Swelling ratio
















82













46 Conclusions












83











84

Chapter 5

COMPUTER SIMULATION








51 Introduction










work





85

























86
















Mass m m





Energy unit ε ε

Time unit τ 1d τ


87


























88


= 1 = 12

Mass 1 12

Mass density 3 3



γ 45 23587

σ 3 23792

ε 1 12

τ 1 2289


water

Non-

charged

PAM

Charged

PAM

Non-

charged

clay

Charged

Clay Counterion

water 13104 13261 10483 13261 4717 13104

Non-charged

PAM 13104 13104 4717 1048 13261

Charged PAM 13104 1048 13261 13261

Non-charged

clay 13104 13104 13261


Counterion 13104


1998)


89



















i

cmiig rrmM

R 2212)(

1





Spitnik 1947)

90

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

3

4

5

5 7 9 11 13

ltR

g2gt

12

pH

(b)


pH

91

apKc

cpH

)

1(log10














35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

(a) (b)


92












(Mt) surface














93

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Poly

mer

Lay

er T

hic

knes

s

pH

(b)



94

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)





95
























96

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

pac

ing

pH

(b)





97












(Figure 56-h)

98

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)






99

















100

1

2

3

4

5

6

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

pac

ing

pH

(b)



101























102

0

10

20

30

40

50

0

5

10

15

1 3 5 7 9 11 13

Sim

ula

ted

Inte

rlay

er

Spac

ing

Sw

elling R

atio

Solution pH

Swelling ratio

















103







57 Conclusions














scale CPN behaviors




104




pH

105

Chapter 6

CONCLUSIONS
















feasible






permeability

106









at neutral pH







properties

107

Future Work























108




















109

REFERENCES





Lafayette Louisiana



Reports 28(1-2) 1-63





Mater 4(6) 1395-1403



Minerals 50(5) 546-552





















158 235-243


Minerals 34(2) 259-273






110





































293-302












111























2328



143-239



NY 125-129















147(1-2) 35-44





Aspects 281(1-3) 82-91

112




York









New York








8593


253-287









5530

















Polymer 20(8) 969-975

113



214102-8







225-246








Science 138 107-147






1-41



34(15) 5267-5274










Physics 125(22)






16(19) 7493-7502



11265-11277



725-736

114



4435















Physics 115(7) 3322-3329
















304-342


Oxford New York












19(1) 84-90

115


Films 233(1-2) 96-111


San Diego















Science 45(4) 270-279



498

















453-551



8(4) 373-468




4(2) 105-123



116



ISS) 1359-1372


162(11) 826-832















15(2) 193-197











1391


Minerals 47(2) 174-180




1399-1407












Chemistry 46(7) 1485-1490

117





693-713



















77(3) 463-466



Science 108(1) 243-248





20(24) 10382-10388


New York London





10(12) 4554-4559










118










160



265(10) 889-896










184101-7


















New York









119















Chemistry C 111(35) 13170-13176









York












Arbor MI 12-49







159(2-3) 491-501



Equilibria 261(1-2) 366-374




120












Minerals 43(3) 285-293



2815-2819

































Chemistry C 111(23) 8248-8259

121




Nature 346 345-347


Rev 74(3) 385-400




Technology B 22(6) 3450-3453


23(5) 715-724


Field Science 218(4571) 467-469




782-789




York


Minerals 30(1) 1-10









282



Physics 121(5) 2367-2375




20954-20964



Materials 5(12) 1694-1696






122






474




38(4) 343-350









3129








Materials 18(4) 432-436





13-20




1231-1253





5(10) 1574-1592



123




3

310

52

25cm

cmg

gV onitemontmorill

3

35

750

753cm

cmg

gV midepolyacryla




mlcmg

g

contentclay

Mass

Vclay

clay

water 1000010

52

253

124


Sample Calculation












L

hhAkQ ab )(


)( ba hhA

LQk

= 1193 x 10-9 ins = 3029 x 10-9 cms

125





3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(a) (b)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(c) (d)

126

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(e) (f)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

(g) (h)



127









(a) (b) (c)



0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

paci

ng

pH

0

5

10

15

20

5 7 9 11 13

Inte

rlay

er S

paci

ng (

nm)

pH

(a) (b)


real unit (nm)


225 nm

128

VITA

Sungho Kim







vii

57 Conclusions 103

CONCLUSIONS 105

Future Work 107

REFERENCES 109





VITA 128

viii

LIST OF FIGURES

































ix







48










pH = 3 6 and 115 63






cell 75











pH 90

x

























real unit (nm) 127

xi

LIST OF TABLES











xii

ACKNOWLEDGEMENTS
























Chapter 1

INTRODUCTION



















1992)




2


























3












11 Motivation



polymer composites







4

12 Objectives

























5




13 Hypothesis



















6



7

Chapter 2

LITERATURE REVIEW






















1999)

8

























9








Si

O

Al

Mg

Na

basal

spacing

096 nm

to ~ infin

Octahedral

sheet

Tetrahedral

sheet

Interlayer

space

Tetrahedral

sheet

10


























11






(2)

(3)

(1)

Surface potential


ζ (zeta potential)






shear

plane

Stern

layer


12



2

0

2

0

2

1

zc

T

Ne

k

av

B






















13


























14
























15










Heimann 1993)
















16

a

CH

NH2

O = C

CH2















+ bNaOH rarr + bNH3



CH2

a-b

CH

NH2

O = C

CH2

b

CH

Na+

O = C

O-

17

a

CH

NH2

O = C

CH2 CH2

b

CH

N+

O = C

O

(CH2)2

(CH3)3

Cl-

+ OH- rarr +




















CH2

n-m

CH

NH2

O = C

CH2

m

CH

Na+

O = C

O- n-m

CH2 CH2

OH N+

(CH3)3 Cl-

18
















Contracted coiled


Partially coiled



at pH gt 105


19


























20


























21



















(a) (b) (c)



22
























23


























24

























25









)exp()tan( i

||

||)tan(

s

p

r

r

sp








261 Overview




26












Quantum




Molecular

Mechanics(atoms)

Chara

cte

ristic

Length

Characteristic Time

mm

μm

nm

pico

seconds

nano

seconds

micro


FEM DEM

(finite elements)



27

























28

L AL

A

(a) (b)

















29




ijF = ijCF + ij

DF + ijRF

ijCF =

cij

cij

ij

ij

c

ij

ij

rrif

rrifr

r

r

ra

0

))(1(

ijDF = -γij∙ω

Dmiddotrijmiddotij

ij

ij

ij

ij

r

rv

r

r )(


Rmiddotrij

ij

ijij

r

r

t








ωD(r) = [ωR(r)]2

σ2 = 2γkBT



c

c

cRD

rrif

rrifr

r

rr

0

)1()]([)(

2

2

30




2























31






32

Chapter 3









31 Introduction















33


polymer



















321 Materials

3211 Bentonite



34






















35


component component

SiO2 6302

Al2O3 2108

Fe2O3 325

FeO 035

CaO 065

MgO 267

Na2O 257

trace 072

LOI 564






Ltd)











(cmolkg) 808


Giese 2001)




(gmol) a

High molecular

weight N300

~ 6 x 106

Low molecular



n

CH

NH2

O = C

CH2

36


























37



125 2 4 8 125 25 and 625























38














7˚)











39





Livermore CA)




















40


Sample

numbera

Clay

content

Polymer

type

pH of

polymer

solution

Clay-to-

polymer

volume ratio

Basal spacing

(nm)b

XRD intensity

at peak

(counts)

N1 0001 na na na

1227 150

N2 001 1166 160

CC1 0001 nPAM 109 8 1526 225

CC4 0005 nPAM 109 8 1509 280

CC7 001 nPAM 1094 8 1515 200

CC10 003 nPAM 111 8 1215 210

MW1 001 nPAM 1094 125 1527 1211 180 180

MW4 001 NPAM 1096 125 1558 1151 130 115

PH1 001 nPAM 41 8 1515 1289 230 180

PH4 001 nPAM 565 8 1515 1308 210 175

PH7 001 nPAM 1094 8 1515 200

CP1 0001 nPAM 109 125 1557 310

CP4 0001 nPAM 11 2 1541 460

CP7 0001 nPAM 1104 4 1504 400

CP10 001 nPAM 111 8 1515 1289 230 180

CP13 001 nPAM 1094 125 1527 1211 180 180

CP16 001 nPAM 109 25 1108 310



tabulated










41

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1479nm1278nm

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1495nm1192nm

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1494nm1253nm









(a)

(b)

(c)

42

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1527nm1211nm

21plusmn2˚C

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1509nm

1005nm

110˚C

(a)

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1558nm1151nm

21plusmn2˚C

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1511nm

1005nm

110˚C

(b)



43




drying stages
















44





(c)

(b)

(a)

(f)

(e)

(d)

-935

-1062

3917

58737

45

2 7 12 17 22 27

Rel

ativ

e In

ten

sity

2θ˚ (CuKα)

15 nm








(a)

(b)

(c)

M M

M M

M M

46

0

100

200

300

400

500

0001 001 01

Inte

nsi

ty (

cou

nts

)

Clay content

















47


























48

0

100

200

300

400

500

1 10 100

Inte

nsi

ty (

coun

ts)
















49



34 Conclusions












consumption










50










51

Chapter 4


NANOCOMPOSITES







41 Introduction














52


























53

42 Materials

421 Clay Minerals
























54


Palomino 2009)


constituent

constituent

Kaolinite

(Supplier Data)


(Murray 1991)

Bentonite

(Supplier Data)

SiO2 456 463 6302

Al2O3 384 398 2108

Fe2O3 04 325

FeO 035

TiO2 15

CaO 006 065

MgO trace 267

K2O 018

Na2O trace 257

trace 072

LOI 1382 139 564









c Supplier data




55

422 Polyacrylamide
















charged units

Molecular

weight (gmol) a

NPAM N300

None ~ 6 x 106


CPAM C494

20)(

ba

b ~ 4 x 106


a

CH

NH2

O = C

CH2

a

CH

NH2

O = C

CH2 CH2

b

CH

N+

O = C

O

(CH2)2

(CH3)3

Cl-

56




















57

(a) (b)



(a) (b)








3 μm 25 μm

5 μm 10 μm

58





















Dn 2

0

))2

sin(4

(



59


constant D

Dt

Tkd B

)(3











10

100

1000

1 3 5 7 9 11 13

Hy

dro

dy

nam

ic R

adiu

s (

nm

)

pH

Mt

nPAM


60


















conformation of CPN






61


solution pH
























62

Detector

Polarizer

Analyzer

Simulated Surface

Polymer

Layer

Thickness



Light




by water (H2O)















63










225

275

325

375

425

0 400 800 1200

Th

ick

nes

s (

Aring)

Time (minutes)

pH asymp 6

pH asymp 3

pH asymp 115

-30

-20

-10

0

10

20

30

0 400 800 1200

Th

ick

nes

s C

han

ge

Δd

d0

()

Time (minutes)

pH asymp 6

pH asymp 3

pH asymp 115

Δd = d - d0

(a) (b)


pH = 3 6 and 115

64










measurement time
















65

























66
























67
















1985)










68

10

20

30

40

50

1 3 5 7 9 11 13

Surf

ace

area

(m

2g

)

pH

Kaolinite

Kaolinite+nPAM

(a)

400

600

800

1000

1200

1 3 5 7 9 11 13

Surf

ace

area

(m

2g

)

pH

Mt+nPAM

Mt

(b)



69



















polymer

442 Swelling Test





70























71

0

1

2

0 24 48 72

Sw

elli

ng r

ati

o

Time (hour)

pH 115

pH 6

pH 3

(a)

0

5

10

15

0 24 48 72

Sw

elli

ng r

ati

o

Time (hour)

pH 115

pH 6

pH 3

(b)



Untreated

Kaolinite

Untreated

Mt

72













and the CPN













73























study

74










ndash were used
















75

Pressure

Control PanelGas

Supply

Influent

Solution Reservoir

Driving Pressure

Confining


Cell

Effluent

Collector


cell















76



10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bil

ity

(cm

s)

pH

Kaolinite+nPAM

Kaolinite+NPAM

Kaolinite+CPAM

Kaolinite

(a)

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bil

ity

(cm

s)

pH

Kaolinite+nPAM

Kaolinite+NPAM

Kaolinite+CPAM

Kaolinite

(b)


and (b) powder-form

77


























78

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bilit

y (

cms

)

pH

Mt+nPAM

Mt+NPAM

Mt+CPAM

Mt

(a)

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bilit

y (

cms

)

pH

Mt+nPAM

Mt+NPAM

Mt+CPAM

Mt

(b)




79

























80














0

10

20

30

40

0

20

40

60

80

100

1 3 5 7 9 11 13

Ad

sorb

ed P

AM

Lay

er T

hic

kn

ess

(nm

)

Hy

dro

dy

nam

ic R

adiu

s (n

m)

Solution pH






81

0

5

10

15

0

10

20

30

40

1 3 5 7 9 11 13

Sw

elling

R

atio

Ad

sorb

ed P

AM

Lay

er T

hic

knes

s (n

m)

Solution pH


Swelling ratio
















82













46 Conclusions












83











84

Chapter 5

COMPUTER SIMULATION








51 Introduction










work





85

























86
















Mass m m





Energy unit ε ε

Time unit τ 1d τ


87


























88


= 1 = 12

Mass 1 12

Mass density 3 3



γ 45 23587

σ 3 23792

ε 1 12

τ 1 2289


water

Non-

charged

PAM

Charged

PAM

Non-

charged

clay

Charged

Clay Counterion

water 13104 13261 10483 13261 4717 13104

Non-charged

PAM 13104 13104 4717 1048 13261

Charged PAM 13104 1048 13261 13261

Non-charged

clay 13104 13104 13261


Counterion 13104


1998)


89



















i

cmiig rrmM

R 2212)(

1





Spitnik 1947)

90

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

3

4

5

5 7 9 11 13

ltR

g2gt

12

pH

(b)


pH

91

apKc

cpH

)

1(log10














35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

(a) (b)


92












(Mt) surface














93

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Poly

mer

Lay

er T

hic

knes

s

pH

(b)



94

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)





95
























96

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

pac

ing

pH

(b)





97












(Figure 56-h)

98

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)






99

















100

1

2

3

4

5

6

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

pac

ing

pH

(b)



101























102

0

10

20

30

40

50

0

5

10

15

1 3 5 7 9 11 13

Sim

ula

ted

Inte

rlay

er

Spac

ing

Sw

elling R

atio

Solution pH

Swelling ratio

















103







57 Conclusions














scale CPN behaviors




104




pH

105

Chapter 6

CONCLUSIONS
















feasible






permeability

106









at neutral pH







properties

107

Future Work























108




















109

REFERENCES





Lafayette Louisiana



Reports 28(1-2) 1-63





Mater 4(6) 1395-1403



Minerals 50(5) 546-552





















158 235-243


Minerals 34(2) 259-273






110





































293-302












111























2328



143-239



NY 125-129















147(1-2) 35-44





Aspects 281(1-3) 82-91

112




York









New York








8593


253-287









5530

















Polymer 20(8) 969-975

113



214102-8







225-246








Science 138 107-147






1-41



34(15) 5267-5274










Physics 125(22)






16(19) 7493-7502



11265-11277



725-736

114



4435















Physics 115(7) 3322-3329
















304-342


Oxford New York












19(1) 84-90

115


Films 233(1-2) 96-111


San Diego















Science 45(4) 270-279



498

















453-551



8(4) 373-468




4(2) 105-123



116



ISS) 1359-1372


162(11) 826-832















15(2) 193-197











1391


Minerals 47(2) 174-180




1399-1407












Chemistry 46(7) 1485-1490

117





693-713



















77(3) 463-466



Science 108(1) 243-248





20(24) 10382-10388


New York London





10(12) 4554-4559










118










160



265(10) 889-896










184101-7


















New York









119















Chemistry C 111(35) 13170-13176









York












Arbor MI 12-49







159(2-3) 491-501



Equilibria 261(1-2) 366-374




120












Minerals 43(3) 285-293



2815-2819

































Chemistry C 111(23) 8248-8259

121




Nature 346 345-347


Rev 74(3) 385-400




Technology B 22(6) 3450-3453


23(5) 715-724


Field Science 218(4571) 467-469




782-789




York


Minerals 30(1) 1-10









282



Physics 121(5) 2367-2375




20954-20964



Materials 5(12) 1694-1696






122






474




38(4) 343-350









3129








Materials 18(4) 432-436





13-20




1231-1253





5(10) 1574-1592



123




3

310

52

25cm

cmg

gV onitemontmorill

3

35

750

753cm

cmg

gV midepolyacryla




mlcmg

g

contentclay

Mass

Vclay

clay

water 1000010

52

253

124


Sample Calculation












L

hhAkQ ab )(


)( ba hhA

LQk

= 1193 x 10-9 ins = 3029 x 10-9 cms

125





3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(a) (b)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(c) (d)

126

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(e) (f)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

(g) (h)



127









(a) (b) (c)



0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

paci

ng

pH

0

5

10

15

20

5 7 9 11 13

Inte

rlay

er S

paci

ng (

nm)

pH

(a) (b)


real unit (nm)


225 nm

128

VITA

Sungho Kim







viii

LIST OF FIGURES

































ix







48










pH = 3 6 and 115 63






cell 75











pH 90

x

























real unit (nm) 127

xi

LIST OF TABLES











xii

ACKNOWLEDGEMENTS
























Chapter 1

INTRODUCTION



















1992)




2


























3












11 Motivation



polymer composites







4

12 Objectives

























5




13 Hypothesis



















6



7

Chapter 2

LITERATURE REVIEW






















1999)

8

























9








Si

O

Al

Mg

Na

basal

spacing

096 nm

to ~ infin

Octahedral

sheet

Tetrahedral

sheet

Interlayer

space

Tetrahedral

sheet

10


























11






(2)

(3)

(1)

Surface potential


ζ (zeta potential)






shear

plane

Stern

layer


12



2

0

2

0

2

1

zc

T

Ne

k

av

B






















13


























14
























15










Heimann 1993)
















16

a

CH

NH2

O = C

CH2















+ bNaOH rarr + bNH3



CH2

a-b

CH

NH2

O = C

CH2

b

CH

Na+

O = C

O-

17

a

CH

NH2

O = C

CH2 CH2

b

CH

N+

O = C

O

(CH2)2

(CH3)3

Cl-

+ OH- rarr +




















CH2

n-m

CH

NH2

O = C

CH2

m

CH

Na+

O = C

O- n-m

CH2 CH2

OH N+

(CH3)3 Cl-

18
















Contracted coiled


Partially coiled



at pH gt 105


19


























20


























21



















(a) (b) (c)



22
























23


























24

























25









)exp()tan( i

||

||)tan(

s

p

r

r

sp








261 Overview




26












Quantum




Molecular

Mechanics(atoms)

Chara

cte

ristic

Length

Characteristic Time

mm

μm

nm

pico

seconds

nano

seconds

micro


FEM DEM

(finite elements)



27

























28

L AL

A

(a) (b)

















29




ijF = ijCF + ij

DF + ijRF

ijCF =

cij

cij

ij

ij

c

ij

ij

rrif

rrifr

r

r

ra

0

))(1(

ijDF = -γij∙ω

Dmiddotrijmiddotij

ij

ij

ij

ij

r

rv

r

r )(


Rmiddotrij

ij

ijij

r

r

t








ωD(r) = [ωR(r)]2

σ2 = 2γkBT



c

c

cRD

rrif

rrifr

r

rr

0

)1()]([)(

2

2

30




2























31






32

Chapter 3









31 Introduction















33


polymer



















321 Materials

3211 Bentonite



34






















35


component component

SiO2 6302

Al2O3 2108

Fe2O3 325

FeO 035

CaO 065

MgO 267

Na2O 257

trace 072

LOI 564






Ltd)











(cmolkg) 808


Giese 2001)




(gmol) a

High molecular

weight N300

~ 6 x 106

Low molecular



n

CH

NH2

O = C

CH2

36


























37



125 2 4 8 125 25 and 625























38














7˚)











39





Livermore CA)




















40


Sample

numbera

Clay

content

Polymer

type

pH of

polymer

solution

Clay-to-

polymer

volume ratio

Basal spacing

(nm)b

XRD intensity

at peak

(counts)

N1 0001 na na na

1227 150

N2 001 1166 160

CC1 0001 nPAM 109 8 1526 225

CC4 0005 nPAM 109 8 1509 280

CC7 001 nPAM 1094 8 1515 200

CC10 003 nPAM 111 8 1215 210

MW1 001 nPAM 1094 125 1527 1211 180 180

MW4 001 NPAM 1096 125 1558 1151 130 115

PH1 001 nPAM 41 8 1515 1289 230 180

PH4 001 nPAM 565 8 1515 1308 210 175

PH7 001 nPAM 1094 8 1515 200

CP1 0001 nPAM 109 125 1557 310

CP4 0001 nPAM 11 2 1541 460

CP7 0001 nPAM 1104 4 1504 400

CP10 001 nPAM 111 8 1515 1289 230 180

CP13 001 nPAM 1094 125 1527 1211 180 180

CP16 001 nPAM 109 25 1108 310



tabulated










41

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1479nm1278nm

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1495nm1192nm

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1494nm1253nm









(a)

(b)

(c)

42

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1527nm1211nm

21plusmn2˚C

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1509nm

1005nm

110˚C

(a)

0

100

200

300

400

Inte

nsi

ty (

cou

nts

)

1558nm1151nm

21plusmn2˚C

0

100

200

300

400

2 7 12 17 22 27

Inte

nsi

ty (

cou

nts

)

2θ˚ (CuKα)

1511nm

1005nm

110˚C

(b)



43




drying stages
















44





(c)

(b)

(a)

(f)

(e)

(d)

-935

-1062

3917

58737

45

2 7 12 17 22 27

Rel

ativ

e In

ten

sity

2θ˚ (CuKα)

15 nm








(a)

(b)

(c)

M M

M M

M M

46

0

100

200

300

400

500

0001 001 01

Inte

nsi

ty (

cou

nts

)

Clay content

















47


























48

0

100

200

300

400

500

1 10 100

Inte

nsi

ty (

coun

ts)
















49



34 Conclusions












consumption










50










51

Chapter 4


NANOCOMPOSITES







41 Introduction














52


























53

42 Materials

421 Clay Minerals
























54


Palomino 2009)


constituent

constituent

Kaolinite

(Supplier Data)


(Murray 1991)

Bentonite

(Supplier Data)

SiO2 456 463 6302

Al2O3 384 398 2108

Fe2O3 04 325

FeO 035

TiO2 15

CaO 006 065

MgO trace 267

K2O 018

Na2O trace 257

trace 072

LOI 1382 139 564









c Supplier data




55

422 Polyacrylamide
















charged units

Molecular

weight (gmol) a

NPAM N300

None ~ 6 x 106


CPAM C494

20)(

ba

b ~ 4 x 106


a

CH

NH2

O = C

CH2

a

CH

NH2

O = C

CH2 CH2

b

CH

N+

O = C

O

(CH2)2

(CH3)3

Cl-

56




















57

(a) (b)



(a) (b)








3 μm 25 μm

5 μm 10 μm

58





















Dn 2

0

))2

sin(4

(



59


constant D

Dt

Tkd B

)(3











10

100

1000

1 3 5 7 9 11 13

Hy

dro

dy

nam

ic R

adiu

s (

nm

)

pH

Mt

nPAM


60


















conformation of CPN






61


solution pH
























62

Detector

Polarizer

Analyzer

Simulated Surface

Polymer

Layer

Thickness



Light




by water (H2O)















63










225

275

325

375

425

0 400 800 1200

Th

ick

nes

s (

Aring)

Time (minutes)

pH asymp 6

pH asymp 3

pH asymp 115

-30

-20

-10

0

10

20

30

0 400 800 1200

Th

ick

nes

s C

han

ge

Δd

d0

()

Time (minutes)

pH asymp 6

pH asymp 3

pH asymp 115

Δd = d - d0

(a) (b)


pH = 3 6 and 115

64










measurement time
















65

























66
























67
















1985)










68

10

20

30

40

50

1 3 5 7 9 11 13

Surf

ace

area

(m

2g

)

pH

Kaolinite

Kaolinite+nPAM

(a)

400

600

800

1000

1200

1 3 5 7 9 11 13

Surf

ace

area

(m

2g

)

pH

Mt+nPAM

Mt

(b)



69



















polymer

442 Swelling Test





70























71

0

1

2

0 24 48 72

Sw

elli

ng r

ati

o

Time (hour)

pH 115

pH 6

pH 3

(a)

0

5

10

15

0 24 48 72

Sw

elli

ng r

ati

o

Time (hour)

pH 115

pH 6

pH 3

(b)



Untreated

Kaolinite

Untreated

Mt

72













and the CPN













73























study

74










ndash were used
















75

Pressure

Control PanelGas

Supply

Influent

Solution Reservoir

Driving Pressure

Confining


Cell

Effluent

Collector


cell















76



10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bil

ity

(cm

s)

pH

Kaolinite+nPAM

Kaolinite+NPAM

Kaolinite+CPAM

Kaolinite

(a)

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bil

ity

(cm

s)

pH

Kaolinite+nPAM

Kaolinite+NPAM

Kaolinite+CPAM

Kaolinite

(b)


and (b) powder-form

77


























78

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bilit

y (

cms

)

pH

Mt+nPAM

Mt+NPAM

Mt+CPAM

Mt

(a)

10E-10

10E-08

10E-06

10E-04

1 3 5 7 9 11 13

Per

mea

bilit

y (

cms

)

pH

Mt+nPAM

Mt+NPAM

Mt+CPAM

Mt

(b)




79

























80














0

10

20

30

40

0

20

40

60

80

100

1 3 5 7 9 11 13

Ad

sorb

ed P

AM

Lay

er T

hic

kn

ess

(nm

)

Hy

dro

dy

nam

ic R

adiu

s (n

m)

Solution pH






81

0

5

10

15

0

10

20

30

40

1 3 5 7 9 11 13

Sw

elling

R

atio

Ad

sorb

ed P

AM

Lay

er T

hic

knes

s (n

m)

Solution pH


Swelling ratio
















82













46 Conclusions












83











84

Chapter 5

COMPUTER SIMULATION








51 Introduction










work





85

























86
















Mass m m





Energy unit ε ε

Time unit τ 1d τ


87


























88


= 1 = 12

Mass 1 12

Mass density 3 3



γ 45 23587

σ 3 23792

ε 1 12

τ 1 2289


water

Non-

charged

PAM

Charged

PAM

Non-

charged

clay

Charged

Clay Counterion

water 13104 13261 10483 13261 4717 13104

Non-charged

PAM 13104 13104 4717 1048 13261

Charged PAM 13104 1048 13261 13261

Non-charged

clay 13104 13104 13261


Counterion 13104


1998)


89



















i

cmiig rrmM

R 2212)(

1





Spitnik 1947)

90

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

3

4

5

5 7 9 11 13

ltR

g2gt

12

pH

(b)


pH

91

apKc

cpH

)

1(log10














35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

(a) (b)


92












(Mt) surface














93

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Poly

mer

Lay

er T

hic

knes

s

pH

(b)



94

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)





95
























96

3

4

5

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

pac

ing

pH

(b)





97












(Figure 56-h)

98

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)






99

















100

1

2

3

4

5

6

0 025 05 075 1

ltR

g2gt

12

Charge Density

(a)

0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

pac

ing

pH

(b)



101























102

0

10

20

30

40

50

0

5

10

15

1 3 5 7 9 11 13

Sim

ula

ted

Inte

rlay

er

Spac

ing

Sw

elling R

atio

Solution pH

Swelling ratio

















103







57 Conclusions














scale CPN behaviors




104




pH

105

Chapter 6

CONCLUSIONS
















feasible






permeability

106









at neutral pH







properties

107

Future Work























108




















109

REFERENCES





Lafayette Louisiana



Reports 28(1-2) 1-63





Mater 4(6) 1395-1403



Minerals 50(5) 546-552





















158 235-243


Minerals 34(2) 259-273






110





































293-302












111























2328



143-239



NY 125-129















147(1-2) 35-44





Aspects 281(1-3) 82-91

112




York









New York








8593


253-287









5530

















Polymer 20(8) 969-975

113



214102-8







225-246








Science 138 107-147






1-41



34(15) 5267-5274










Physics 125(22)






16(19) 7493-7502



11265-11277



725-736

114



4435















Physics 115(7) 3322-3329
















304-342


Oxford New York












19(1) 84-90

115


Films 233(1-2) 96-111


San Diego















Science 45(4) 270-279



498

















453-551



8(4) 373-468




4(2) 105-123



116



ISS) 1359-1372


162(11) 826-832















15(2) 193-197











1391


Minerals 47(2) 174-180




1399-1407












Chemistry 46(7) 1485-1490

117





693-713



















77(3) 463-466



Science 108(1) 243-248





20(24) 10382-10388


New York London





10(12) 4554-4559










118










160



265(10) 889-896










184101-7


















New York









119















Chemistry C 111(35) 13170-13176









York












Arbor MI 12-49







159(2-3) 491-501



Equilibria 261(1-2) 366-374




120












Minerals 43(3) 285-293



2815-2819

































Chemistry C 111(23) 8248-8259

121




Nature 346 345-347


Rev 74(3) 385-400




Technology B 22(6) 3450-3453


23(5) 715-724


Field Science 218(4571) 467-469




782-789




York


Minerals 30(1) 1-10









282



Physics 121(5) 2367-2375




20954-20964



Materials 5(12) 1694-1696






122






474




38(4) 343-350









3129








Materials 18(4) 432-436





13-20




1231-1253





5(10) 1574-1592



123




3

310

52

25cm

cmg

gV onitemontmorill

3

35

750

753cm

cmg

gV midepolyacryla




mlcmg

g

contentclay

Mass

Vclay

clay

water 1000010

52

253

124


Sample Calculation












L

hhAkQ ab )(


)( ba hhA

LQk

= 1193 x 10-9 ins = 3029 x 10-9 cms

125





3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(a) (b)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(c) (d)

126

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

3

4

5

0 5 10 15

ltR

g2gt

12

Time (μs)

(e) (f)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

35

45

55

0 5 10 15

ltR

g2gt

12

Time (μs)

(g) (h)



127









(a) (b) (c)



0

10

20

30

40

50

5 7 9 11 13

Inte

rlay

er S

paci

ng

pH

0

5

10

15

20

5 7 9 11 13

Inte

rlay

er S

paci

ng (

nm)

pH

(a) (b)


real unit (nm)


225 nm

128

VITA

Sungho Kim







AN ENGINEERED CLAY SOIL SYSTEM USING FUNCTIONAL …

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