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Sol-Gel Nano Materials and Process
MS512 Nano Technology
Prof. Byeong-Soo Bae
Prof. Byeong-Soo Bae Dept. of Materials Sci. & Eng.
I. IntroductionII. Chemistry of Precursors SolutionsIII. Sol-Gel Process of SilicaIV. Sol-Gel Process of Complex Oxides
(Ferroelectrics)V. Sol-Gel Process of Hybrid MaterialsVI. Sol-Gel Process of Mesoporous
Materials
Text:1. A. C. Pierre, Introduction to Sol-Gel Processing, Kluwer Academic
Publisher, 19982. C. J. Brinker, G. W. Scherer, Sol-Gel Science, Academic Press,
1990
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I. Introduction
MS512 Nano Technology
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• Sol-gel Processing
Sol-gel processing is a wet chemical route to synthesis of a colloidal suspension of solid
particles or clusters in a liquid (sol) and subsequently to formation of a dual phase material of
a solid skeleton filled with a solvent (wet gel) through sol-gel transition (gelation). When the
solvent is removed, the wet gel converts to a xerogel through ambient pressure drying or an
aerogel through supercritical drying. Thin (~ 100 nm), uniform and crack-free films can be
readily formed on various materials by dip, spin, or spray-coating; thick films can be obtained
by multiple coatings.
In the sol preparation, the precursors (either organic or inorganic) undergo two chemical
reactions: hydrolysis and condensation or polymerization, typically with acid or base as
catalysts, to form small solid particles or clusters in a liquid (either organic or aqueous
solvent). The solid particles or clusters are so small (1~1,000 nm) that gravitational forces are
negligible and interactions are dominated by van der Waals, coulombic and steric forces. Sols
are stabilized by an electric double layer, or steric repulsion, or their combination.
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Colloid: a suspension in which the dispersed phase is so small ( 1~1000 nm) that gravitational forces are negligible and interactions are dominated by short-range forces, such as Van der Waals attraction and surface charges.
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Sol: a colloidal suspension of solid particles in a liquid .
Gel: a solid network filled with a second phase of colloidal dimensions, either liquid or gas that also forms a three dimensional inter-connected network.
Gelation: also called sol-gel transition that begins with the formation of solid fractal aggregates that grow until they extends throughout the sol.
Xerogel: a gel in which the solvent has been removed by evaporation at an ambient environment.
Aerogel: a gel in which the solvent has been removed by supercritical drying. An aerogel typically has a porosity >75% and a BET surface area > 1000 m2/g.
Supercritical drying: a process of removing the liquid from the pores of wet gel above the critical temperature and critical pressure.
Precursor: a starting compound for preparation of a colloid (or sol). It consists of a metal or metalloid element surrounded by various ligands. It includes inorganic salts and organic compounds.
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Hydrolysis: a chemical reaction in which hydroxyl groups become attached to the metal atom by replacing the ligands in the precursor.
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Condensation (or polymerization): A process that hydroxyl groups merge to form metal- oxygen-metal bonds, while releasing a water molecule, resulting in formation of solid particles or clusters through combining monomers, growth of particles or clusters, and linking of particles or clusters into chains and networks that extend through the sol.
Steric force: a repulsion which results from polymers adsorbed to the interacting surfaces. The physical basis of the steric repulsion is a combination of a volume restriction effect arising from the decrease in possible configurations in the region between the two surfaces and an osmotic effect due to the relatively high concentration of adsorbed polymers in the region between the two surfaces as they approach one another.
Electric double layer: forms at the vicinity of a solid particle in a sol. When a solid submerges into a liquid, the surface will be electrically charged and subsequently an electric double layer forms due to the combination of coulombic, entropic and other specific forces. When two particles approach each other, as soon as the double layers overlap, a repulsive electrostatic force arises to prevent two solid particles to aggregate so that the sol is stabilized.
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Sol-gel processing is a simple technology in principle but has required considerable effort to
become of practical use. Sol-gel enables materials to be mixed on an atomic level and thus
crystallization and densification to be accomplished at a much low temperature. However, a true
atomic level homogeneity in a multiple component system is an endeavor; the difficulty arises
from the fact that the chemical reactivity varies greatly from precursor to precursor. Precursor
modification and step-wise partial hydrolysis are the common approaches to homogeneity in
multiple component systems.
The advantages of the sol-gel process in general are high purity, homogeneity, and low
temperature. For a lower temperature process, there is a reduced loss of volatile components and
thus the process is more environmental friendly. In addition, some materials that cannot be made
by conventional means because of thermal and thermodynamical instability, can be made by this
process. The sol-gel process has many applications in synthesis of novel materials. Examples
include aerogels used in space crafts to capture stellar dust, xerogels as matrix in biosensors, and
high power laser materials.
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Condensation
RO OH
OR
OR
M RO OR
OR
OR
M RO O
OR
OR
M+ OR
OR
OR
M
RO OH
OR
OR
M HO OR
OR
OR
M ROO
M
OR OR
+ HOH
OR
OR
M+
OR
+ ROH
Hydrolysis
RO OR + H
2O
OR
OR
M RO OH
OR
OR
M + ROH
Alkoxides:M(OR)n M= Si,Ti,Zr,Al
R= -CH3, -CH2CH3
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•Definitions of Sol-Gel Process
Alkoxide Sol-Gel
• Dislich - Procedure to prepare the multicomponent oxides that are homogeneous at the atomic level� should include the colloidal coprecipitates of hydroxides and oxyhydrates� restrict to the gels synthesized from metal alkoxides
Coloidal Sol-Gel
• Segal – Production of inorganic oxides either from colloidal dispersion or from the metal alkoxides
� non-oxides such as nitrides and sulfides, and organic-inorganic hybrids
• Colloidal route used to synthesize ceramics with an intermediate stage including a sol and/or gel state
• Production of inorganic oxides either from colloidal dispersion or from the metal alkoxides
• Chemical processing to synthesize ceramics glasses, and hybrids from wet chemicals
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• Inorganic Polymerization
Monomer
Solution
Dimer Oligomer
O
M
O
OO M
O
O
O M
O
O
O M
O
O
O
Sol
Gel
O
M OO M
O
O M
O
O
O
M
O
OO M
O
O
O M
O
O
O
O O O
O M O O M O M O
O O O
M OO M O M O M M
O
OO M
O
O
O
M
O
OO M
O
O
O M
O
OO
O M
O
O M O
O
M
O
O
O
M OO M
O
O M
OOxide
O M
O O
M OO M
O
O
M
O
OO M
O
O M
O
O M
O
O M O
O
M
O
O
Solid
ColloidGelation
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DryingSintering
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Processing of Sol-Gel Materials
• Powders
• Monoliths
• Fibers
• Coatings and Thin Films
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• Porous Materials and Aerogel
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Melting and Sol-Gel Process for Glass Fabrication
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Advantages and Disadvantages of Sol-Gel Process
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• Advantages • Disadvantages
High purity from raw materials High cost of raw materials
Good homogeneity from raw materials Large shrinkage during processing
Low processing temperature Residual fine pores and hydroxyls
Good shape ability Health hazards of organic solution
Production of new composition glasses Easily cracking during the drying stage
Long processing times
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Characteristics of Sol-Gel Process
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D Low temperature process of fine ceramics and glasses
D Bottom-up fabrication from chemicals
D Aqueous-based chemistry and process
D Immobilization & encapsulation over wide range of sizes, chemistries and functions
D Mild & easily controlled conditions
D Molecular level dispersion
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Fabrication of Sol-Gel Optical Fiber Preform
정화소결
혼합 및 캐스팅 탈착 건조
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Sol-Gel Coatings on Display
Silica layerAR layers
CCoonndduuccttiivvee layer
GlassLight
1.0% of incident light<Interference effect>
Antiglare
R G B
Phosphor
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• Preparation of Nano Materials by Sol-Gel Processing
Solution Glass, Ceramics
Heated gel
Sol Dry gel
Wet gel졸 - 겔 생성물
Porous gels
Pores
Gels dispersed with organic
molecules
Inorganic- organic
composites
CeramicsGlassGels dispersed with inorganic or metal particles
Organic moleculesOrganic polymer Inorganic network
Particles
Grains
<100C
<150C
<500C
<1200C
<100C
미세구조
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나노구조재 나노하이브리드 나노복합체나노복합체
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II. Chemistry of Precursors Solutions
Precursor Solution
• Chemical PrecursorChemical reactant which contain the cation M present
in the final inorganic sol or gel
Metallic salts - MmXn, eq) AlCl3
Metal alkoxides – M(OR)n, eq) Al(O Organometalic compounds
• SolventsWaterNon-aqueous solution
Protic solvent Aprotic solvent
Acidic solvent Basic solvent Amphoretic solvent
C2H5)3
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Hydrolysis of Metal Salts Solution
• Ions SolvationDissolution is solution
MX � Mz+ + Xz- in the solution
Cation solvationSolvatation shell [M(H2O)N]Z+
• HydrolysisDeprotonation of a solvated metal cation
Aquo ligand H2O � hydroxo ligand(OH-)or an
• Formation of Hydroxo LigandsSolvated metal: an acid, Water: Lewis base
[M(OH2)N]Z+ + hH2O ⇔ [M(OH)(OH2)N-1](z-1) + + H3O+
acid + Lewis base ⇔ conjugates base conjugated acid
[M(OH)h(OH2)N-h] “aquo-hydroxo” complex
oxo ligand(O2-)
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• Formation of Oxo LigandsDeprotonation of an hydroxo ligand
[M(OH)(OH2)N-1](Z-1)+ + hH2O ⇔ [MOh(OH2)N-h] (Z-h)+ + hH3O+
acid+ Lewis base ⇔ conjugated base + conjugated acid
[MO(OH2)N-1]z-2 “aquo-oxo ligand “ complex
[M(OH2)N]Z+ + hH2O ⇔ [M(OH)(OH2)N-1](z-1) + + H3O + hH2O ⇔ [MOh(OH2)N-h] (Z-h)+ +
hH3O+
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h=0 : [MONH2N]Z+
aquo-ion0<h<N :
[M(OH)X(OH2)N-x](Z-X)+
hydroxo-aquo complex
h=N : M(OH)N](N-Z)-
hydroxo complex N<h<2N : [MOX(OH)N-x](N+X-Z)-
oxo-hydroxo complexh=2N
: [MON](2N-Z)-
oxo-ion
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Condensation of Metal Salt Solution
• Condensation and PolymerizationHydroxo ligand (M-OH) � “ol” bridge (M-OH-M) � “oxo” bridge (M-O-M)
• Condensation by OlationFor the low charge cations – dissociative SN1 mechanism
H2OM ⇔ -M- + H2O -M-OH + -M- ⇔ M-OH-M-
For the higher charge cations – nucleophilic addition reaction AN
-M-OH + -M-OH ⇔ M-OH-M-OH
For the transition elements – associative SN2 mechanism
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• Condensation by OxolationFor the low charge cations – dissociative SN1 mechanism
H2OM ⇔ -M- + H2O -M-OH + -M- ⇔ M-OH-M-
For the higher higher charge cations – nucleophilic addition reaction AN
-M-OH + -M-OH ⇔ M-OH-M-OH
For the transition elements – associative SN2 mechanism
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Alkoxide PrecusorsAlkoxides:M(OR)n M= Si,Ti,Zr,Al
R= -CH3, -CH2CH3
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Hydrolysis of Metal Alkoxides
• HydrolysisAlkoxy group (OR) � Hydroxo(OH) or Oxo(O) ligands
(1) Nature of alkoxy group(2) Nature of solvent
(3) Concentration in solvent
(4) ) Water to alkoxide molar ratio rw = [H2O]/[alkoxide]
(5) temperature
• Formation of Hydroxo Ligands M(OR)z + H2O M(OH)(OR)z-1 + ROH
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• Hydrolysis of Silicon AlkoxideAcidic solution (pH < 2.5)
- Negatively charged particles- [H3O]+ attack the oxygen in alkoxy group
• Formation of Oxo Ligands Lewis base Water vapor
Basic solution (pH > 2.5)- Positively charged particles- OH attacks the Si in alkoxides
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Condensation of Metal Alkoxides
• Condensation by Olation SN2 nucleophilic substitution mechanism -
• Condensation of Oxolation Transfer of the H to an OR ligand Transfer of the H to an OH group
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• Condensation of Silicon Alkoxides Acidic solution (pH < 2.5)
- Two – step SN2 type mechanism condensation- Protonation of silanol group- Hydrolysis is faster than condensation- Linear polymer
Basic solution (pH > 2.5)- Deprotonation of silanol group- Condensation is faster than hydrolysis- Dense solid
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Precursor Mixing
• Mixing Two Alkoxides Double alkoxides
- Mixing two alkoxides in same non-aqueous solvent
Simultaneous hydrolysis of simple alkoxides- Simultaneous refluxing in solvent
Matching the hydrolysis rates of different alkoxides- Partially hydrolyzed Si(OR)4 and Al(OR’)3
• Mixing Two Metal Salts
• Mixing a Alkoxide with a Metal Salt
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III. Sol-Gel Process of Silica1
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1 Aqueous Silicate
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Kinetics of hydrolysis and condensation is slower
• Polymerization at pH 2 - 7Proportional to [OH-]3-D gel network by aggregationHydrolysis with water
• Polymerization above pH 7 - 10Stable solParticle growth rather than aggregationThermal decomposition
• Polymerization below pH 2Proportional to [H+]Metastable
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1 Silicon Alkoxide Sol-Gel
hydrolysis
estrification
alcohol condensation
Si- OR + H 2O
Si- OH + ROH
alcoholysis
water condensation
S i- O R + HO- Si Si- O- Si + ROH
hydrolysis
S i- O H + HO- Si Si- O- Si + H 2O
• Precursor Solution
Silicon alkoxide + water + alcohol + catalyst
H2O:Si molar ratio (r) – 1~ over 50
Concentrations of acids or bases – 0.01 ~ 7 M
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• Tetraalkoxysilanes Si(OR)4 : TEOS(tetraethoxysilane),
TMOS(tetramethoxysilane)
• Organoalkoxysilanes R‘nSi(OR)3 : MTMS(Metyltrimethoxysilane),
DMDMS(Dimetyldimethoxysilane)
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Precursor Molecules
• Molecular Building Blocks Hexamethoxydisiloane
OctamethoxytriethoxtsilaneMethoxylated cubic octamer - Silsiquioxane
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1 Hydrolysis of Silicon Alkoxides
• Effects of Catalyst
• H2O/Si Ratio (r)
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1 • Steric and Inductive Effects
• Effects of Solvents Protic solvent enhance hydrolysis
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1 Condensation of Silicon Alkoxides
• Effect of Catalyst Minimum at about pH 1.5
Maximum at intermediate pH Acid catalyzed
condensation (pH<2)– protonated silanol
Base catalyzed condensation (pH>2)
– deprotonated silanol
• Steric and Inductive Effects
Acidity of silanol – higher pH IEP
Basicity of silanol – lower pH IEP
In acid-catalyzed,steric effects > inductive effects
• Effects of Solvent Protic solvent – acid-
catalyzed condensation Aprotic solvent – base-
catalyzed condensati
on
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1 Structural Summary
• Low pH ConditionHydrolysis rate > condensation rateCluster-cluster growth – network structure
• High pH ConditionUnhydrolyzed monomersMonomer-monomer growth - particles
• Intermediate pH ConditionMinimum hydrolysis rate – rate limiting
• General Condition Acid catalyzed, low water system – drawing fiber Acid catalyzed, high-water system – bulk gels Base catalyzed, high-water system – particles
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1
Sol-Gel Ferroelectrics
• Metallorganic PrecursorsMetal alkoxides
Zr n-propoxide [Zr(OC3H7)4]Ti isopropoxide [Ti(OCH(CH3)2)4] Ethoxides, Butoxides
Inorganic or organic salts La nitrate
Pb acetate
• SolventsPrimary solvent - stablization
Chemical modifiers-methoxyethanol, acetic acid glycol
Chelating agents- -diketone (acetylacetone)
Secondary solventEthylene glycol, propanol, methanol or water Control in viscosity, pH, surface tension
Lead Titanium Zirconium
Gelation Control Firing Additives
Viscosity Adjustment
Precursor Solution
Dipping,Spraying or Spin Coating
Crystallization 400-700 ºC
Drying and Organic Removal280-400ºC
Multilayer Coatings
Alcohol or Water
IV. Sol-Gel Process of Complex Oxides
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• Solution Process of Electo or Optical Ceramics
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1
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Preparation of Ferroelectric Solutions
• Alcohol-Based SolutionPb acetate trihydrate, Ti isopropoxide, Zr n-propoxide2-methoxyethanol + 2-methoxyethanol/waterChange to methoxides and partial hydrolysis
• Water-Based SolutionPb acetate trihydrate, Ti isopropoxide, Zr n-propoxideAcetic acid + water, propanol, glycolsHydrolysis with water
• MOD SolutionPb acetate, Ti acetylacetonate, Zr acetate
Pb 2-ethyl hexanonate, Ti isopropoxide, Zr tetra-n-butoxideWater + methanol, hexaneThermal decomposition
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Fabrication of Ferroelectric Films
Sr metal Ba metal
2-Methoxyethanol 2-Methoxyethanol
0.4M precusor solution
Drying
2-Methoxyethanol
DistillationTi isopropoxide
Coating
Heat Treatment for Crystallization
Iteration
In dry N2 gas
Coating
Drying
Heat Treatment for Crystallization
Nb(OC2H5)5
2-Methoxyethanol
Iteration
Refluxing (12h)
0.1M SBN sol
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Distillation
Refluxing
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Preparation of Stable Solution
• Dilution
Pb acetate trihydrate, Ti isopropoxide, Zr n-propoxide
2-methoxyethanol + 2-methoxyethanol/water
Change to methoxides and partial hydrolysis
• Chemical Modification and Complexation
Pb acetate trihydrate, Ti isopropoxide, Zr n-propoxide
Acetic acid + water, propanol, glycols
Hydrolysis with water
• Surface Modification of Nanoparticles
Stablization of particles
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IV. Sol-Gel Process of Hybrid Materials
size 분산상의 크기
mm
m
1nm
1Å
복합재료
폴리머 / 폴리머 유리입자 / 폴리머 유리섬유 / 폴리머
세라믹 / 폴리머 금속 / 폴리머 세라믹 / 금속
(FRP,FRC,FRM)
Nanocomposite
Nanohybrid
물리적 혼합
물성은 복합 법칙에 따름
복합법칙에 따르지 않는 새로운 물성이
발견됨
수소결합 화학결합
신물성
Physical
hybridization
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hybridization
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Class I (Nanocomposite)D Organic dyes embedded in sol-gel matrix
Organic dyes, inorganic ions or molecules + silica, aluminosilicate, zirconia, titania
� fluorescence, photochromic, non-linear optical properties
D Inorganic particles embedded in a polymer
Inorganic particles + polymer blend
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D Organic monomers embedded in sol-gel matricesPolymerizable organic monomer + sol-gel inorganic matrices
Polymerization
Sol-gel
D Polymers filled with in-situ generated inorganic particles
Inorganic particle formation by sol-gel reaction in a polymer matrices
Sol-gel
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Polymerization
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D Simultaneous formation of interpenetrating organic-inorganic networks
Alkoxides functionalized by liable plymerizable group
Sol-gel
Polymerization
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D Obtension of ordered organic-inorganic structures
Insertion of organic molecules polymers into an anisotropic inorganic network
Build anisotropic inorganic particles using organic molecules and self assembled aggregates
Sol-gel
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Class II (Nanohybrids)
D Organically modified silicon alkoxides
R’xSi(OR)
4-x
Polymerization
Sol-gel
D Polyfunctional alkoxysilanes
(RO)3Si-R’-Si(OR)3
Sol-gel
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D Alkoxysilanes functionalized by polymers(RO)3Si-Polymer-Si(OR)3
Sol-gel
D Surface modification by organoalkoxysilanes
Polymerization
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D Template building blocks
Polymerization
D Ordered hybrid materialsSelf-assembly of molecular units on surface hydroxyl groups
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Hybrids from Sol-Gel Process of Organoalkoxysilanes
Network modifier ( R' : unreactable)
CnH2n+1-Si(OR)3
Si(OR)3
H2N-(CH2)3-Si(OR)3
CF3-(CF2)n-(CH2)2-Si(OR)3
methyl, ethyl
phenyl
amino
fluoro
Network former ( R' :polymerizable)
H2C CH-O-(CH2)3-Si(OR)3
Oepoxy
O
O-(CH2)3-Si(OR)3methacrylate
HS-(CH2)3-Si(OR)3
C Si(OR)3
H2C
H
mercaptopropyl
vinyl
R
R
R inorganic
= O
= Si,Ti,Zr,...modifier
entrapped molecule
R
organic polymeric chain
Modification Functionalization
Crosslinking
R’nSi(OR)4-n
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D Compensation of Characteristics
Y Hard and Stable Y Soft and Flexible Y Easy ProcessY Cheap
D Functionalization Y Modification Y New function
D TransparencyY Optical materialsY Functional coating
Silica Network
Polymer Network
Heterometal NetworkOrganic Modification
ORMOCER, CERAMER, POLYCERAM,Hybrid Sol-Gel Glass, Hybrid Polymer, HYBMRIMER
ORMOCER, CERAMER, POLYCERAM,Hybrid Sol-Gel Glass, Hybrid Polymer, HYBMRIMER
Sol-Gel Hybrid Materials (HYBRIMER)
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Characteristics of HYBRIMERD Transparency
D Functionality
D Compensation of Characteristics
D Modulation & Tunability of Characteristics
D Easy Process & Fabrication
D High Thermal & Chemical Stability
D Easy Encapsulation with Better Compatibility
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Transparency of HYBRIMERD Hybrids of molecular level
D Coloration by doping of dyes or colloids
D Application of optics, display, and coatings
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Compensation of Characteristics
Ref.: Fraunhofer ISC
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Compensation of Characteristics
D Compensation of Polymer and Glass Properties
High
Low
Hardness
450 -950
90 -250
Thermal Stability
1.35 – 1.95
High
-8 to 6
-10 to 160
4 -130
1.40 - 1.65
Low
-140 to -85
150 to 700
1 -10
Refractive index
Dielectric Constant
dn/dT (10-7℃)
Thermal Expansion
Young’s Modulus
(Mpa)
Glass
Polymers
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Compensation of CharacteristicsD Mechanical Properties Silica/PDMS
HYBRIMER
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Functionality of HYBRIMERD Hydrophilic and Hydrophobic
Coatings
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Optical Application of HYBRIMERD Solid state dye laser materials
D Rare-earth emission materials
D Nonlinear optical and photorefractive materials
D Photochemical hole burning materials
D Photochromic materials
D Optical sensor matrials
D Optical waveguide materials
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Functionality of HYBRIMER
Unpoled Polymers
Poled Polymers
amplitude, wave form E-O Modulators
• heating around Tg• electric field on• cooling• electric field off
SHG
EO
EOspatial, wave frontSpatial Light Modulators
wave length change Frequancy Doubling
(a)
(b)
(c)
Unpoled Sol-Gel Hybrids
Poled Sol-Gel Hybrids
이광섭 교수 , 한남대
HC
l / DM
F- C
H3 O
H
- H2 O
D NLO Chromophore HYBRIMER
(OEt)3Si Si(OEt)3
NL
O
O O
Si
O
O
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O
Si
Si
O OO Si
O
Si
OSi
Si
OO OO
Si
OO
SiSi
O
SiO O
SiO
Si
O
O
Si
Si O
O
Si O O
O Si
O
Si
Si
O
O O
O
Si
O
Si
OO O
SiO
NLO
NL
O
NLO
NL
O
NLO
NLO
NL
O
NLO
NL
O
NL
O
NLO
NLO
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Silica vs. Polymer forWaveguide Materials
SSiill
iicca
a
PPoolly
ymmee
rr
Spin-on Low
temp. Easy, Cheap
Versatile
FHD,CVDHigh temp
Difficult,Expensive.
Process
Absorption Mechanical Thermal
Lowe
r
Hig
h
Hig
h
Lo
w
Lo
w
Lo
w
Thermo-optics Design
Functionality
High
Versati
le
Versati
le
Lo
w
No
t
No
t
Polarization dependence
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Stress
Anisotropy
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Advantages of HYBRIMER Waveguide
Silica Waveguide
Sol-Gel Silica Waveguide
Manipulation of refractive index in a broad range Easy fabrication
Easy incorporation of inorganic/organic doponts
HYBRIMER Waveguide
Manipulation of refractive index in a broad range
Thermally and chemically stable
Hardness for end facet polishing
Thick films without cracks Hydrogen bonding to stabilize
organic dopants
Photoimprinting, Easy process
Polymer Waveguide
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Micro-Patterning in HYBMRIMER by Photo-polymerization
Photoh-initiator
R'=CH3;C2H4OH= - C3H6OOC -
Selective etchingUV
developing
Fabrication of waveguides
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Encapsulation & Immobilization in HYBRIMERD Entrapment of biomolecules and chemical species in
porous structureD Better compatibility in organic environmentsD Applications in biosensor, bioreactors, chemical sensor, catalysis
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VI. Sol-Gel Process of Mesoporous Materials• Micelle Structure
Spherical micelle
Cylindrical micelle
Lamellar micelle
Inverse micelle
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• Ordered Mesoporous Materials Hexagonal packing of cylindrical micelles Cubic packing of spherical micelles Planar packing of micellar micelles
• Fabrication Procedure Micellar rods with a surfactant � micelles in a hexagonal array � add inorganic
precursor solution in a polar solvent � array of hollow oxide cylinders – organic
heart elimination by washing or by calcination
Micelles with inorganic precursor solution
HexagonalCubic
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LamellarCubic
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• Surfactants Alkyl-ammonium halide (cationic surfactant)
[CnH2n+1N(CH3)3]X- , X=Cl or Br Cetyltrimethylammonium bromide (CTAB)
Poly(oxyethylene) non-ionic surfactant [n-alkylpolyethylene glycol ethers]
CH3(CH2)n-1(OCH2CH2)mOH = CnEOm Brij 56, C16H33(OCH2CH2)10OH
Poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide)
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• Pure Silicate CompositionLiquid Crystal Templating Mechanism• Silica source – TEOS, Ludox, fumed silica, sodium silicate
Alkyltrimethylammonium halide surfactant - cetyltrimethylammonium bromide (CTAB)
Base - sodium hydroxide or tetramethylammonium hydroxide (TMAOH)Water
Silicate Rod Assembly
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Silicate Layer Puckering Charge Density Matching
Folding Sheets
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Silicatropic Liquid Crystals
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General Liquid Crystal Templating Mechanism: Electrostatic Mechanism
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• Applications Catalysis
- High Surface Areas and Thermal Stability Sorption and Separation Inclusion of Nanostructured Materials Optical Applications
- Dye Inclusion
- Nanocrystals (Quantum Dots)
- Organometallic Complexes
- Polymer Inclusions
- NLO and Laser Materials
- Photochromic Materials Chemical Sensors
Insulator Materials
Low k Materials Hydrogen Storage and Electrode Materials
- Carbon Nanotubes
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