BioInspired Nanocomposites

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Bio-Inspired Nanocomposites

• Princeton University
• Northwestern University
• University of California Santa Barbara
• University of North Carolina Chapel Hill
• National Institute of Aerospace

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Bio-Inspired Nanocomposites

• Motivation
• Nanotube-based composites
• Nanotubes as themselves
• Polypeptide bionanocomposites
• Understanding the interphase
• Graphene-based composites
• Why graphite?
• CREGO Chemically reduced GO composites
• TEGO Thermally exfoliated GO composites

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Smart Aerospace Vehicles
Mechanical, Electrical, Dielectric, Thermal in
one Entity
Health Monitoring
Superstrong Structure
Multifunctional Structural
Sensing
Sensing/Actuation
Superstrong Structure
Actuation
Anti-Static
Health monitoring
Actuation
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Motivation

• Structure Multifunction
• Surface area and interfaces ? 104 increase
• Fundamentally alter polymer
• Small vol ? huge impacts on properties
• Strategy
• Work with SWCNT
• Develop novel graphene- and nanoplatelet-based
  systems
• Design morphology and interphase
• Develop hybrid composites

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Nanotube-Based Composites

• NU-UNC-NIA
• Brinson, Daniel, Papanikolas, Park, Ruoff

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Structural Multifunctional Nanomaterials

• Requirements for Structural Multifunctional
  Nanomaterials for Aerospace Applications

Functional polymer Functional
nanoinclusions (SWCNT)

• Lightweight
• Mechanically durable
• Sensing/actuation
• Radiation protection
• Electrical conductivity
• Thermal conductivity
• Health monitoring
• Self healing
• Energy generation
• Energy storage

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Tensile Test Experimental Setup

• AFM cantilevers used as manipulation
• tools and force-sensing elements

Experimental Setup
Tensile Test Schematic
Nanomanipulator inside SEM vacuum chamber
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MWCNT Sword-in-Sheath Fracture
Inner shells
outer shell
SEM images of sword-in-sheath fracture of a MWCNT
under tension
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MWCNT Tensile Testing Results
Only the outer shell bears the tensile
load Clamp failed before tube fracture
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Mechanical response until failure of SWCNTs ?
Is the Space Elevator feasible or not?

• Collaboration with Alan Cassell, NASA Ames
• - Growth of small SWCNT bundles
• - Collaboration extended also to colleagues at
  Columbia University

• Home-built cantilever to have correct stiffness
• Diving board platforms to have suspended
  SWCNTs
• Mechanics of Space Elevator Nicola Pugno and
  Rod Ruoff
• (in progress)

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SWCNT-PMMA Designed Interphase

• 1 wt SWCNTs in PMMA
• As received SWCNTs
• Amide functionalized SWCNTs

PMMA
a-SWCNT
PMMA tethered to a-SWCNT
(Ramanathan, et al., Chemistry of Materials 2005)
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SWCNT/PMMA Dispersion and Interphase

• Amide functionalized
• PMMA, 1wt a-SWCNT

• PMMA, 1 wt asreceived SWCNT

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SWCNT/PMMA Dispersion and Interphase

• As-received tubes lead to
• Local clustering
• Localization of interphase
• zone
• Bulk PMMA and discrete
• interphase zones

• Functionalization leads to
• Improved dispersion
• Larger interphase zone
• Disappearance of bulk PMMA

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SWCNT/PMMA Model and Experiment

• Simple, elastic stiffness
• Model is random orientation of straight, perfect
  NTs in bulk PMMA

(Ramanathan, et al., J. Polym. Sci. B, 2005)
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SWCNT/PMMA DMA Results
Unmodified NTs
Functionalized NTs
(Ramanathan, et al., J. Polym. Sci. 2005)
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Interphase Hypothesis

• Discrete interphase region
• More mobile interphase
• Less mobile interphase
• Continuous interphase
• Higher volume fraction
• Functionalized nanoparticles
• Gradient interphase
• Ellis Torkelson data on distribution of Tgs
• in thin films
• How choose gradient and properties?
• Molecular modeling
• Local experimental data

Peak shifting
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Viscoelastic Hybrid Model
Discrete interphase layer
Less mobile interphase
More mobile interphase
G Matrix G Composite
Matrix is all interphase
Loss Shear Moduli, G

• PC data for matrix
• Interphase properties shifted
• matrix properties
• Modeling supports experimental
• results/hypothesis

Less mobile interphase
Frequency, w
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Bio-Inspired BioNanocomposite
SWCNT
Leucine-Phenylalanine
OM 5 SWNT/LF


Out-of-plane Strain
Strain (mm/mm)
Electric Field (MV/m)
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Bio-Inspired BioNanocomposites
SWNT/Polypeptide Composite Stabilization

• Multiple, Cooperative Stabilization Mechanisms
• 'Shape' Compatibility
• ?? ?-helices are stiff, semi-flexible
  macromolecules
• like SWCNTs
• Reduces depletion interactions that would
  increase mixing entropy
• 'Chemical' Compatibility
• Phenylalanine residues in polypeptide provide ?
  - ? interactions
• with SWCNTs
• Total binding energy not strongly dependant on
  leucine/phenylalanine
• sequence
• Electrostatic Matrix Stabilization
• Anti-parallel tetramers of ?-helices expand to
  hexamers
• to accommodate SWCNTs
• Leads to increase in number of favorable
  dipolar interactions

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HRSEM 2SWCNT-LF BioNanocomposite
Excellent dispersion of SWCNTs through
well-designed copolypeptide matrix
3-Dimensional Nanodispersion of SWCNTs
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Mechanical Reinforcement BioNanocomposites
Arbitrary Units
Physical Properties
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Toughness SWCNT/Copolypeptide
BioNanocomposites
Force (N)
Toughness (mJ/kg)
325 Increase at 5wt
Displacement (mm)
SWCNT Concentration (wt)
Nanotube Bridging Crack-Path Deflection
Nanocracking/Debonding Crack Pinning
Toughness Increase
Physical Entanglement
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Ultrafast Spectroscopy of SWCNT/Polymer
Composites
Strategy Analyze the dynamics of the EXCITED
STATE SPECTRA to understand interface or
interphase environment of SWCNTs
Excite SWCNT with visible/NIR photon ? Create
electron-hole (e-h) pair Follow (e-h) dynamics
with femtosecond transient absorption spectroscopy

• Experiments probe the photoexcited state...
• Excited-State Energetics
• Observation Energies of high-energy SWNT bands
  are altered by interaction of SWNT with polymer
  (low-energy bands are not affected)
• Charge-Carrier Dynamics after excitation
• Charge carrier cooling
• (e-h) Recombination dynamics
• Plasmon relaxation

Styers-Barnett et al, J. Phys. Chem. A109 289
(2005)
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SWCNT/Polymer Interaction

• Our data suggest
• States near Fermi energy do not appear affected
  by polymer
• Higher energy bands are stabilized by more
  interacting polymers
• Origin of interaction is not clear...is it
  electrostatic or does it involve mixing of
  polymer and SWNT states?

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Bio-Inspired Nanocomposites

• Motivation
• Nanotube-based composites
• Nanotubes as themselves
• Polypeptide bionanocomposites
• Understanding the interphase
• Graphene-based composites
• Why graphite?
• CReGO Chemically reduced GO composites
• TEGO Thermally exfoliated GO composites

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Graphene-Based Nanocomposites

• Northwestern-Princeton-UNC
• Aksay, Brinson, Daniel, Prudhomme, Ruoff

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Novel Approaches with Graphite
Generation of very thin platelets by top down
approaches 6 years ago
X. K. Lu, H. Huang, N. Nemchuk and R. S. Ruoff,
Patterning of highly oriented pyrolytic graphite
by oxygen plasma etching, Appl. Phys. Lett., 75,
193-195 (1999). Not very bio-inspired, though!
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We need a bottom up and gentle synthetic
approach Bio-inspiration!
2004 USGS survey 100,000,000 metric tons of
natural graphite exist 750,000 metric tons of
natural graphite mined, processed, and used in
2004 250,000 metric tons of synthetic graphite
made and used in 2004
Graphite sells for dollars per pound
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Structural Aspects of Graphite

• sp2-bonded carbon atoms
• Interlayer separation (d0) 3.34 Å
• (Ic 6.9 Å)
• Layers are held together by weak van der Waals
  forces
• 1100 GPa modulus (in-plane)
• Density 2.2 g/cc
• 3000 W/m-K (in-plane)
• Semi-metal (in-plane)
• Open to the full repertoire of synthetic organic
  chemistry for chemical tuning

How to disassemble graphite into individual
sheets to exploit its remarkable in-plane
properties?
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Approaches to Graphene-Based Composites

• Expanded graphite
• Graphite Oxide (GO)
• TEGO - Thermally exfoliated GO
• CReGO - Chemically reduced GO
• PIGO - Phenyl
• Isocyanate GO

EG
GO
TEGO

• Targets
• Individual sheets (2600 m2/g)
• Readily dispersed in polymers
• Retain inherent mechanical, thermal, electrical
  properties of graphene
• Dramatically improved composite properties

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Disadvantages of EG and GO

• Expanded Graphite
• Retain multilayer stacks
• Surface areas lt100m2/g
• Graphite Oxide (GO)
• Hydrophilic not dispersable in most hydrophobic
  organic polymers
• Highly oxidized material non-conducting
• However

easy to make large quantities
Additional processing TEGO, CReGO, PIGO
Reduce so material is conducting Retain
individual sheets Render dispersable in
polymers

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Graphene Nanoplatelets from GO
Solution process Chemical removal of oxygen
from exfoliated individual platelets under
comparatively mild conditions
Graphene oxide
-O
Graphene
13C NMR of GO and hydrazine-reduced GO (Alfred
Kleinhammes, UNC Chapel Hill)
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Reduced GO Nanoplatelets CReGO

• Reduction of GO nanoplatelets leads to
  precipitation and irreversible agglomeration
• The precipitated material cannot be re-dispersed

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Chemically Functionalized Platelets

• Surface hydroxyl groups of GO can be chemically
  modified by derivatization with organic
  isocyanates
• Isocyanate-treated GO loses ability to exfoliate
  in water but exfoliates in polar aprotic solvents

AFM of Phenyl isocyanate-treated GO exfoliated in
DMF
S. Stankovich, et al., Chem. Commun., to be
submitted.
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CReGO Nanocomposites
1) PS 2) N,N-dimethylhydrazine
Phenyl isocyanate- treated graphite oxide
DMF ultrasound
Dispersion of exfoliated GO nanoplatelets
Dispersion of reduced GO nanoplatelets with
polymer

• Reduction without polymer results in
  agglomeration of the reduced platelets
• Polymer coats reduced nanoplatelets and prevented
  their agglomeration, giving true nanocomposite

methanol
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Wavy Leaves, Tethered Membranes,and Bio-Inspired
Nanocomposites
Diffraction pattern of a single graphene sheet
embedded in polystyrene. The rings are at 4.18
Å, 2.43 Å, 2.11 Å and 1.41 Å, matching graphene
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CReGO/PS Electrical Resistance Measurements

• Polystyrene basic properties
• Density 1.05 g/cm3
• Electrical conductivity 10-16 S/m
• Thermal Conductivity 0.08 W/(m-K)

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TEGO Thermally Exfoliated GO
reduce
oxidize
Graphite
Graphite Oxide
TEGO
expand
exfoliate
No functionality
Hydrophilic
Some functionality
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TEGO Thermally Exfoliated GO
Graphite Oxide
TEGO

• 500-fold volume expansion upon rapid heating
• XRD shows complete exfoliation of the graphene
  sheets
• Truly unique material SAXS pattern is similar to
  unlayered graphene sheets found on the core of
  presolar graphite

0.2 g
0.2 g
Fraundorf, P. Wackenhut, M. Astrophysical
Journal 2002, 578, L153.
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TEGO Intercalation and Exfoliation
Graphite Oxide d 7.1 nm
Graphite
TEGO Cluster edge
TEGO AFM h 2.8 nm
TEGO
(BIMat team paper submitted to Science)
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TEGO Flakes on Graphite (HOPG)
Processing sequence

• Disperse TEGO in NMP(1-methyl-2-pyrrolidinone)
  by sonicating in an iced bath.
• Centrifuge for several cycles.
• This procedure leaves 25 of the TEGO (and the
  smaller ones) in the supernatant as determined by
  TGA.
• Spin-coat the resulting supernatant on highly
  oriented pyrolytic graphite (HOPG).

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AFM Imaging of TEGO Single Sheets

• TEGO on HOPG
• Tapping mode AFM in ambient conditions
• Wrinkled structureThus, sheet thickness is
  defined by the lowest height
• At the lowest height, the sheet thickness is 1
  nm, corresponding to a single sheet (in GO d
  0.71 nm)
• Most sheets have a thickness of lt 2 nm
• Percentage of the single sheets and the aspect
  ratio distributions have to be determined

(position dashed line above)
HOPG Structure
Images by H.C. Schniepp
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Exfoliation of Graphite Oxide
BET Surface Area Measurements
Untreated sample

• Surface area of TEGO depends on both sample
  preparation and exfoliation temperature
• Maximum surface area reported 400 m2/g

Vacuum-dried
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Synthesis of TEGO Nanocomposites
High speed shear mixing Silverson shear mixture,
MA, USA
Polymer in THF
6000 rpm for 60min for graphite Bath sonication
for 60min for SWCNTs
Anti-solvent for precipitation of the composite
Nanofiller in THF
Filtered and dried _at_80C under vacuum
Hot Press molding
Thin films pressed _at_ 2000 pounds at 210C for 10
mins.
Bath sonication Branson 3510, 335 W
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TEGO Interaction with Polymer
1 wt ARG in PMMA
1 wt TEGO in PMMA
1 wt EG in PMMA
TEGO Exfoliated graphite via thermal expansion
of graphite oxide Good dispersion and interface
ARG, EG As-received, expanded graphite Moderate
dispersion, poor interface

Nanocomposite Fracture surfaces
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TEGO Nanocomposite
Thin sheets wrinkled in situ ? interaction with
polymer
Remarkable Tg shift of 30?C with 0.05 loading of
TEGO!
(BIMat team paper submitted to Science)
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TEGO-PMMA Benchmarking
PMMA/1wt Nanoinclusion
Normalized values
PMMA values E-2.1 GPa, Ultimate strength -
70 MPa Tg 105?C, Thermal degradation
temperature - 295?C
(BIMat team paper submitted to Science)
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TEGO-PMMA Electrical Response

• AC impedence spectroscopy
• Increased conductivity with loading fractions
• Percolation at 1-2 wt

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Graphene-Based Nanocomposites

• GO - derived nanoplates show great promise as
  nanofiller for polymers (CReGO, PIGO, TEGO)
• Simple, scalable approaches
• Surface functionality tunable for a given polymer
• Dispersion of individual sheets!
• Economically viable composites with superb
  thermal, mechanical, and electrical properties
• Scaling processing to larger coupons, hybrid
  composites.

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Processing of Nanocomposites
Schematic of shear mixing

Shear mixing
Step 1 Shearing of expanded graphite into GNPs.
Shear
Diffusion
Step 2 Exfoliation by combined shear/diffusion
processes.
3-Roll Mill Mixer
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Processing of Nanocomposites
Processing methods
Direct mixing
Shear mixing
Combined sonication and shear mixing
Sonication mixing
Ultrasonic processor
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Expanded Graphite/Epoxy Nanocomposites
Intercalated graphite
Expanded graphite
Graphite nanosheets (GNPs)
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Hybrid Nano/Micro Composite
Expansion/ Surface Modification
Intercalation/ Exfoliation

Natural Graphite
Nanocomposite
Epoxy Resin
Modified EG or TEGO/CREGO

Curing
Lightweight Structure
RTM
Fiber Reinforcement
Hybrid Nano/Micro Composite
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Bio-Inspired Nanocomposites Summary

• Excellent composites with SWCNT
• Bioinspired
• Interphase design
• Multifunctional
• New paradigm for graphene-based composites
• CReGO
• TEGO
• Outstanding results
• Comparable/improved wrt SWCNT, plus scalable and
  
• cost-effective
• Realistic platform for large scale aerostructures