IRG II: Mechanomutable Materials: Overviewweb.mit.edu/cortiz/www/IRG/IRG Site Visit 2012_All...

Materials which vary mechanical behavior in response to external influence. Inherent

(chemical/material/molecular) mechanomutability

Geometrically-controlled mechanomutability

intra/intermolecular interactions cross-linking,

configurational entropy

individual geometric units: rod, beam, cell, tube,

curvature

assembly of geometric units: spacing/density, arrangement,

connectivity/percolation

(Cohen, Rubner, Boyce, Ortiz, et al., Adv. Mater. 2011)

IRG II: Mechanomutable Materials: Overview

Potential Applications: switchable shock absorbers, adaptable tissue engineered scaffolds, dynamic cell substrates, particle transport in microfluidic devices, adaptable armor, pressure sensors

Global Objective: ○To provide new fundamental scientific information by exploring new areas of mechanics of materials via the development of an emerging class of “mechanomutable” materials; i.e. materials with stimulus responsive, tunable and novel mechanical behavior

Near Term Goals: ○ To understand, control and direct responsive mechanochemicaltransduction processes○ To explore the coupling between inherent material mechanomutableand architectural (geometric) design ○ To fabricate mechanomutablecomposite systems with new functionalities and tunability

IRG II: Mechanomutable Materials: Objectives

(III) Multiscale Modeling and Predictive Materials Design

(II) Structure-Mechanical Property Relationships

microstructurally -specific continuum

finite elementmodeling (assembly of

geometric units)

Mechanomutable Heteronanomaterials

(I) Design, Synthesis and Self-Assembly

atomistic(molecular

Interactionssingle polymer

chain mech.props)

mesoscale, course-grained

(single geometric unit)

nanoscalecoarse-grained(LBL assembly,

“inherent” material properties)

Create New MaterialsDesign, Synthesis,

Self-Assembly, Fabrication

Understand / PredictMultiscale Modeling

Predictive Materials Design

MeasureStructure-Mechanical

Property Relationships

Hammond

Balazs Boyce Ortiz

Five MIT engineering departments: Mechanical, Chemical, Civil, Materials, and Biological. One collaborator from Chemical Engineering, U. Pittsburgh.

New Mechanics

Cohen

Van Vliet

Buehler

IRG II: Mechaomutable Materials: General Approach & Team

Ross

IRG II: Mechanomutable Model Systems

○ pH-Responsive polyelectrolytemultilayer (PEM) tube forests(Adv. Mater. 2010, Soft Matter 2010, JEMT 2010)

○ Chemo(mechano)responsiveBelousov-Zhabotinsky(B-Z) self-oscillating gels (Soft Matter 2011, Adv. Func. Mater. 2012)

○ Electrochemically responsive macromolecular systems (ACS-Nano 2009)

New: ○ Architecturally-mutable materials and composites (e.g. wrinkling, origami folding, interdigitation, percolation, etc.) via 3D printing

Atomistic nano-mechanics (chemistry)

Nanoscale, coarse-grained

Mesoscale, coarse-grained Continuum (structurally-specific finite element modeling)

• intra and intermolecular interactions, e.g. Fadhesion• nanomechanics of individual polymer chains, e.g. Eb, Ea

• inherent material properties of polymer LBL assembly, e.g. Efilm

• mechanical props. of singlegeometric unit: e.g. Etube

• effective mechanical props. of assembly of geometric constituents, e.g. Etube forest

Buehler, Ortiz+ Soft Matter Boyce, Ortiz+ JEMT

IRG II: Mechanomutable Materials:Multiscale Modeling and Predictive Materials Design

IRG II: Mechanomutable Materials:Multiscale Modeling and Predictive Materials Design

Buehler+ Nature, 2012 (cover article)

1. Full atomistic fundamental "building blocks".

2. Determination of molecular structure (first hierarchy; assembly of building blocks).

3. Mechanical characterization of components.

4. Up-scaling to relevant hierarchies (this step can also be used to inform continuum-based models (e.g., FE). Depending on the system, the number of intermediate "hierarchies" may be variable.

5. Up-scaling to system-level behavior. Mechanical properties can be directly related to atomistic components. The effect of molecular variation can immediately be expressed at the system level.

6. Mechanical characterization of system. Test suite to characterize system-level performance, validated by experimental results.

7. Atomistic interpretation. From the performance and predictions of system-level analysis, assess the effect of molecular variation. If needed, change fundamental "building blocks". Repeat steps in iterative loop.

Model System #1: pH-Responsive Polyelectrolyte Multilayer (PEM) Tube Forests

pH 5.5

pH 2.0

O OH

n

O O-

n

poly(acrylic acid)

poly(allylaminehydrochloride)

NH2

n

NH3+

n (less swollen, stiffer)

(more swollen, compliant)(Cohen, Rubner, et al., Langmuir 2009; Ortiz, Boyce, Cohen, Rubner, et al., Adv. Mater. 2011)

“Inherent” Mechanomutability(Chemical/Molecular Origins)

● Ionic crosslinks between the charged carboxylate (COO-) and ammonium (NH3+) groups exist.

● Swelling occurs due to protonation of the PAA carboxylate groups which induce rupture of the ionic complexation, as well as create osmotic forces and charge repulsion among the free positively charged amine groups.

Changes in mechanical properties are also induced by the increase in molecular rigidity due to ionization. Currently there is a lack of quantitative knowledge of this effect for weak polyelectrolytes. Full atomistic simulations directly measure the persistence length as a function of ionization (pH).

(Ortiz, Buehler,+in preparation 2012)


“Inherent” Molecular Mechanomutability

PAA

Atomistic-level steered molecular dynamics (MD) simulations used to investigate the pH tunable molecular adhesion properties of a polyelectrolyte complex consisting of PAA and PAH

Using steered molecular dynamics (SMD), computational results mimic AFM experimental approaches and can be compared to previous experimental studies (Ortiz, Hammond, Van Vliet)

pH

(Ortiz, Buehler et al. Soft Matter, 2010)


“Inherent” Mechanomutability (Chemical/Molecular Origins)

• Quantify the adhesion energy per length of polymer.

• Due to ionization, can increase adhesion strength×3

• However, stiffness changes of films change order of magnitude or more.

Simulations allow testing of complete phase space

Optimaladhesion @ pH ≈ 5.5 to 6.0


(Ortiz, Buehler et al. Soft Matter, 2010)

“Inherent” Mechanomutability : Tunable Molecular Adhesion

Molecular Coarse-Graining: Simulated Layer-by-Layer Assembly

LbL neither completely random nor ordered. Structure driven by self-assembly.

Replicate the deposition process – controlled “random” assembly

CNTs: Cranford and Buehler, Nanotechnology, 2010; Amyloid plaques: Paparcone, Cranford, and Buehler, Nanoscale, 2011

Applications beyond polyelectrolyte LbLassembly:

1. Filtration processes (e.g., “Buckypaper”)

2. Protein aggregation

Carbon nanotube “Buckypaper”:

Amyloid plaques (associated with Alzheimer's disease)

CG polymers

Full atomistic Generalized model can be fitted for any functional group


(Ortiz, Rubner, Cohen, Buehler, +in preparation 2012)

pH 5.5

pH 2.0

O OH

n

O O-

n

poly(acrylic acid) or PAA

poly(allylaminehydrochloride) or

PAHNH2

n

NH3+


(swollen, compliant)


inherent molecular-level mechanomutability

PAA/PAH tube forest fabrication

anisotropic cylindrical geometry

(Cohen, Rubner, et al., Langmuir 2009; Ortiz, Boyce, Cohen, Rubner, et al., Adv. Mater. 2011)

inter-tube contact

pH 5.5 discrete tubes

pH 2.0

O OH

n

O O-

n

poly(acrylic acid)

poly(allylaminehydrochloride)

NH2

n

NH3+


(more swollen, compliant)

10 μm


(Cohen, Rubner, et al., Langmuir 2009; Boyce, Ortiz, Cohen, Rubner, et al., Adv. Mater. 2011)

din = 0.36±0.11 μmdout = 1.17±0.18 μmH = 12.17±0.57 μm

din = 0.48±0.25 μmdout = 1.81±0.29 μmH = 18.01±1.03 μm

• AFM-based nanoindentation was conducted on PAH/PAA planar film (70 BL) and tube forests with different geometries; outer/inner diameters (10, 15 and 20 BL).

• PAH/PAA PEM is much more compliant at pH 2.0 than pH 5.5 due to breaking of ionic cross-links. Tube forests also show different indentation from the film, explained by microstructure-specific finite element modeling .

• Coupling between inherent mechanomutability and geometrically-induced deformation mechanisms (bending, buckling, twisting), not only contact splitting.

film (70 BL) tube forest (20 BL)tube forest (10 BL)

tube forest (10 BL)

tube forest (20 BL)

film(70 BL)

Finite Element simulationsMises stress


(Boyce, Ortiz, Cohen, Rubner, et al., Adv. Mater. 2011)



Finite element analysisno inter-tube contact at pH 2.0inter-tube contact at pH 2.0

“geometrically-controlled”

• Upon swelling at pH 2.0, a transition from discrete tube bending/buckling to continuous multiaxial deformation due to inter-tube contact (15, 20 BL) was observed→ beyond contact splitting.



• Upon swelling at pH 2.0, a transition from discrete tube bending/buckling to continuous multiaxial deformation due to inter-tube contact (15, 20 BL) was observed→ beyond contact splitting

“inherent”“geometrically-controlled”

(Ortiz, Cohen, Rubner, Boyce et al., Submitted 2012)


MechanomutabilityMaterials which vary mechanical behavior in response to external stimulus.

Inherent(chemical/material/molecular)

mechanomutabilityGeometrically-controlled

mechanomutability

intra/intermolecular interactions cross-linking,

configurational entropy

individual geometric units: rod, beam, cell, tube,

curvature

assembly of geometric units: spacing/density, arrangement,

connectivity/percolation

(Ortiz, Boyce, Cohen, Rubner, et al., Adv. Mater. 2011)

Geometrically-Controlled Mechanomutable Materials

O NH

n

poly(N-isopropylacrylamide)(PNIPAAm)

Low critical solution temperature (LCST)-type transition

• PNIPAAm undergoes LCST-type of phase transition at 32°C, accompanied with changes in volume and mechanical properties.

• Synthesis of PNIPAAm gel in different geometries will enable temperature-induced change in the hydrogel shape, and therefore deformation mechanisms.

• The proof-of-concept can be demonstrated by the variety of shapes that will be fabricated via 3D printing to introduce different mechanical phenomena coupled to inherent mechanomutability:

1) percolation 2) suture 3) interdigitation

New Directions:Architecturally-mutable materials and composites

Ortiz, Boyce,+ unpublished 2012macro-meso-micro-nano

poly(N-isopropylacrylamide)(PNIPAAm)

Low critical solution temperature (LCST)-type transition

• PNPIAAm gels prepared via redoxpolymerization at room temperature undergoes temperature induced swelling/deswelling, which results in changes in its geometry that prepared via 3D-printed molds.

• The geometry change can introduce changes in mechanical deformation mechanisms, such as the presence/absence of interdigitation, and bending/buckling.

New Directions:Architecturally mutable materials and composites

22 ºC

(mor

e sw

olle

n)

37 ºC

(less

sw

olle

n)

1 cmOrtiz, Boyce,+ unpublished 2012

● An architecturally mutable composite is fabricated from a 2D/3D geometrically structured non-responsive component embedded in a responsive matrix (e.g. gel)● Upon the application of a stimulus, the responsive matrix changes dimension (i.e. swells, shrinks) causing the geometry of the non-responsive component to change reversibly (e.g. wrinkling)● A novel 2D analytical model is derived for a sandwich structure with an undulating interface (inspired by plant cell assembles) subjected to in-plane compression

New Directions:Architecturally-mutable materials and composites:

Boyce+ unpublished 2012

31

0

131

00

24)1)(3(

EEvv

tl

cr

32

031

131

20

20 )1()3(125 EEvvcr

Local instability of the

shell various geometricproperties

11 , vE

00 , vEtl PP

zx

Parametric Study of Hexagonal Cells01 / EE

100

50

5

)(mmt1 2 4

Higher E1/E0, longer wavelength, lower critical stress

New Directions:Architecturally-mutable materials and composites:


• PMMA mold made from laser cutter and PDMS networks

• Other geometric or material variations of the network

New Directions:Architecturally mutable materials and composites


Poly(NIPAAm-co-Ru(bpy)3) gel

Ru(bpy)33+Ru(bpy)3

2+

BZ reaction

R. Yoshida et al, JACS 118, 5134 (1996)

Poly(NIPAAm-co-Ru(bpy)3) gel • Catalyst grafted to polymer• Uniform distribution of Ru catalyst exhibits reversible self-oscillating redox reaction in acidic media (Belousov-Zhabotinskyreaction).• BZ reaction in gel causes periodic, autonomous color change and volumetric expansion (swelling)•Provides first opportunity to validate computational predictions of Balazs et al. Science 2006.

3+2+

3+

3+2+ 2+

H2O

Ru

Model System #2: Chemo(mechano)responsive self-oscillating B-Z gels

Poly(NIPAAm-co-Ru(bpy)3) B-Z gel • For gels of sufficiently small dimensions, swelling & color change are uniformly synchronized.• Sustained self-oscillatory responses over hour timescales!

Green (+3) oxidation state

Orange (+2) oxidation state

Color (normalized RG

B) 0.1 mm

(video frame rate accelerated 500x)

Synchronized mechanical & chemical oscillations


Swellin

g (normalized

gel area)

Van Vliet, Balazs+ Soft Matter 2010

Model System #2:Chemo(mechano)sensitive self-oscillating B-Z gels

Heterogeneity: Chemical oscillations vary with aspect ratio

[1] Balazs+, Science (2006) 314: 798[2] Balazs, Van Vliet+ Soft Matter 2010

3 mmSIMULATION EXPERIMENT

SIMULATIO

NEXPERIM

ENT

osc = 1 min 2 min 2.3 min

• Balazs et al. have developed a model predicting chemical pattern formation as a function of aspect ratio [1]. • These images and movies represent the first experimental validation of those dimension-dependent heterogeneities in chemical patterning [2].• New finding: period of chemical oscillation osc also depends directly on gel aspect ratio and volume [2]

Polyacrylamide-silica composite in which ferroin metal catalyst is electrostatically bound. similar to the Ruthenium BZ catalyst, the ferroin catalyst oscillates between its reduced (+2) state and its oxidized (+3) state.

Wave patterns in gels of dimensions >0.6 mm depend on geometry. Chemomechanical oscillations: synchronized color and volume change in gels of dimensions <0.6 mm.

Experiment: Chen, Balazs, Van Vliet et al.Soft Matter 7 (2011) 3141

Model System #2:Chemo(mechano)sensitive self-oscillating B-Z gels

Van Vliet, Balazs+ Soft Matter 2010

Macroscopic mechanical compression induces BZ oscillations in initially non-oscillatory gel

Non-oscillatory state obtained by submerging gel in BZ reactants for 20 hrs Critical stress required to trigger reaction ~0.7 kPa.

“Mechanical resuscitation”


(Van Vliet, Balazs, + Adv. Func. Mater. 2012)

Communicating pressure sensor arrays

• BZ gel discs spaced by gap of 0.23 mm.

• Only Disc 1 was compressed.

• Both discs oscillated, demonstrating that the gels can “communicate.”

• Gaps of 0.31 and 0.52 mm prevented chemical “communication” of mechanical pressure cue.

Model System II: Chemo(mechano)responsive self-oscillating B-Z gels

(Van Vliet, Balazs,+ Adv. Func. Mater. 2012)

Heterostructured BZ gel: spatially localized catalyst Synchronized oscillations between patches of BZ catalyst depends on distance between patches.

Heterostructured patches of BZ catalyst within gel may lead to directional waves or uniform swelling.

Simulation prediction:Yashin Balazs et al. Phys. Review 79 (2009) 046214


(Van Vliet, Balazs,+ in preparation 2012)

Introduce spatial heterogeneity in patterned gels

Gap distance ~ 0.4 mm Gap distance ~ 0.2 mm

Elevated temperature in NIPAAM gels

Locally applied pressure induces oscillations at the deformation site

Locally applied pressure induces propagating oscillations at elevated

temperatures

catalyst-rich gelcatalyst-free gel

(Van Vliet, Ross, + unpublished)


Micro-pump

Wave of swelling

BZ gel

Neutral gel

Perforatedmembrane

BZ gel

Introduce spatial heterogeneity in homogeneous gels

Internal flaws (“perforations”)New route for controlling chemical responseAchieve new functionality for pumps, membranes, stress sensors

Surface flaws (“pac man”)Encompasses spatially varying stress fields Establish how chemical patterns affected by local stress variations

(Van Vliet, Balazs+ unpublished)


Model System #3:Electrochemically-responsive nanoparticle and nanofiber films

Layer-by-layer thin film nanocomposite: (Linear polyethyleneimine / Prussian Blue)30

•Successfully integrated an electrochemical cell with a spectroscopic ellipsometer, AFM, and instrumented nanoindenter

•Film swelling and stiffness controlled rapidly and reversibly by application of an electric potential

Hammond, Ortiz, Van Vliet+ ACS Nano 2009, 3(8), 2207-2216

Model System #3:Electrochemically-responsive nanoparticle and nanofiber films

• Film stiffness controlled rapidly and reversibly by an order of magnitude via application of an electric potential

Layer-by-layer thin film polyaniline nanofiber composites + insulating polyethyleneimine and polyacrylic acid

• Successfully established electrochemical percolation between conducting polymer nanofibers embedded in an insulating polymer matrix

Hammond, Ortiz, Van Vliet+ ACS Nano 2009, 8(3), 2207-2216

IRG II: Mechanomutable Materials: Accomplishments

● Developed, fabricated and studied a new class of “mechanomutable” materials which enables the investigation of fundamentally new mechanical phenomena;

- geometrically-controlled mechanomutability- mechanomutable friction- self-oscillation- spatially directed mechanochemical transduction- signaling and “mechanical resuscitation”

● Established a comprehensive multiscale theoretical framework driving the design of new materials; balance between mechanisms; inherent rigidity of system and crosslinking are major competing interactions at molecular level →

ARCHITECTURALLY-MUTABLE COMPOSITES

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