graphene synthesis & graphene/polymer …...graphene 0-d: bucky ball, 1986 1-d: carbon nanotube,...

Graphene Synthesis & Graphene/Polymer Nanocomposites

Ken-Hsuan (Kirby) Liao Advisors: Dr. Chris Macosko

Dr. Andre Mkhoyan

Department of Chemical Engineering & Materials Science University of Minnesota

Ph.D. Defense Minneapolis MN

September 19th, 2012

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• University of Minnesota - Ph.D. Materials Science, 2008~Present Graphene Synthesis & Graphene/Polymer Nanocomposites

• Double Bond Chemical Co - Research & Development Engineering, 2008 Polymeric Materials

• Taiwan Army, 2007~2008

• National Taiwan University - M.S. Polymer Science & Engineering, 2005~2007 MS Thesis: Thermoplastic polyurethane composites for dental materials - B.S. Chemical Engineering, 2001~2005 BS Thesis: Mechanical & thermal properties of thermoplastic polyurethane

Biography

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Graphene

0-D: Bucky Ball, 1986

1-D: Carbon Nanotube, 1991

3-D: Graphite, 1500

2-D: Graphene, 2004

Graphene Properties

Modulus 1 TPa

Strength 130 GPa

Electrical Conductivity 6000 S/cm

Surface Area 2600 m2/g

Graphene: monolayer of carbon atoms packed in 2D hexagonal manner

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Why Graphene/Polymer Nanocomposites?

Light-weight stiff materials

BMW i8, a car made with composites.

Boeing 787, contains 70,000 lb composites.

Food packaging

From Brown Machine LLC

Conductive coating

From Thermal Spray Technology Inc 4

Picture From Mission Impossible 4 From Boeing

Challenge of Graphene/Polymer Nanocomposites: Dispersion

Bicerano, Polymer, 2002, 43, 369 5

aspect ratio

>> <<

material needed

Motivation of Novel Graphene Synthesis

Criteria of Graphene Synthesis Process for Nanocomposites:

1. Massive production 2. Low cost 3. Environmental friendly process 4. Easy to transport

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Graphene Precursor: Graphite Oxide

• Hydrophilic (Carbon/Oxygen=2/1) • Electrical insulator

GO/water hydrophilic

Graphene/water hydrophobic

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Gao, W. et al, Nature Nanotechnology 2011, 6, 496

Approaches to Produce Graphene

2000oC/s Scotch tape surfactant

Li et al, Nature Nanotechnology 2008, 3, 101

Schniepp et al, J. Phys. Chem. B 2006, 110, 8535

Novoselov et al, Science 2004, 306, 666

Lotya et al, JACS 2009 131, 3611

hydrazine

Oxidation

H2SO4

KMnO4

4 weeks cleaning up

• Advantages: Pristine graphene • Disadvantages: Low Production

• Advantages: High Production • Disadvantages: Slow process Low bulk density Hard to transport Safety issue

Graphite Scotch Tape Nobel Prize

• Advantages: High Production Higher bulk density • Disadvantages: Hazard chemicals Slow process 8

Process & Mechanism of Aqueous Graphene

0.95 nm 0.34 nm

XRD:

Liao, K.-H. et al, ACS Nano, 2011, 5, 1253-1258 9

Process & Mechanism of Aqueous Graphene

0.95 nm 0.34 nm

AFM topography:

1. Liao, K.-H. et al, ACS Nano, 2011, 5, 1253-1258 2. Liao, K.-H. et al, ACS Applied Materials & Interfaces, 2011, 3, 2607-2615

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Process & Mechanism of Aqueous Graphene

Liao, K.-H. et al, ACS Nano, 2011, 5, 1253-1258

ARG Surface Area:

~400m2/g by BET

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Elemental Composition of Aqueous Graphene (ARG)

GO/water hydrophilic

ARG/water hydrophobic

FTIR: XPS: C/O=2/1

C/O=7/1

1. Liao, K.-H. et al, ACS Nano, 2011, 5, 1253-1258 2. Liao, K.-H. et al, ACS Applied Materials & Interfaces, 2011, 3, 2607-2615

TEM: HR-TEM: Dispersion in water:

ARG

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Electrical Conductivity of Aqueous Graphene

C/O Electrical Conductivity(S/cm)

GO Film 2/1 ~10-5

GS Film 7/1 ~101

Graphene Paper

Liao, K.-H. et al, ACS Nano, 2011, 5, 1253-1258

• Advantages: High production High bulk density

• Disadvantages: Slow process Hazard chemicals

Chemically Reduced Graphene: Aqueous Reduced Graphene:

• Advantages: High production High bulk density Fast process No hazard chemicals involved

Single-layer graphene yield: 65% Single + double layer yield: > 90%

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Dispersion of ARG in TPU

Single solvent blending process: Co-solvent blending process:

Percolation concentration 1.75 wt% Percolation concentration 0.5 wt% Modulus improved by ~300% (3.0 wt%) Modulus improved by ~650% (3.0 wt%)

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Resistance Modulus

Graphene/Poly-Urethane-Acrylate (PUA) Nanocomposite

ano2

Idea: Disperse graphene in flowable oligomer instead of polymer for better dispersion Graphene: Vorbeck’s thermally reduced graphene (TRG)

15 Liao, K.-H. et al, Polymer, 2012, 53, 3756

Electrical Percolation & Aspect Ratio

Percolation concentration: 0.15 wt% Af of dispersed TRG: ~750 reported Af of free standing TRG: 750

Af : aspect ratio of dispersed filler σc : conductivity of nanocomposites σf : conductivity of filler r : particle radius t : particle thickness Φsphere : volume fraction of interpenetrating spheres (= 0.29) Φperc : percolation volume concentration

σc = σf (φ-φperc)t

16 Liao, K.-H. et al, Polymer, 2012, 53, 3756

Mechanical Properties of Graphene/PUA Nanocomposites

Polymerization heat & Tg by DSC:

DMA : Polymerized Graphene/Poly-urethane-acrylate Nanocomposites:

TRG Load (wt%) Hp (J/g) Tg (°C) 0 245±16

14±4

0.10 244±13 0.25 256±22 0.50 243±15

Mori-Tanaka model simulated results (black dash lines) & real modulus (spots):

17 Liao, K.-H. et al, Polymer, 2012, 53, 3756

Electrical Percolation Concentration : Literature Summary

18 Liao, K.-H. et al, Polymer, 2012, 53, 3756

Motivation: Egraphene/Ematrix literature summary

Kim, Abdala, Macosko Macromolecules 2010

0.05 wt% in PMMA Brinson et al Nature Nano 2008

Theoretical Maximum

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Glass Transition Temperature of Graphene/PMMA Nanocomposites

Ramanathan et al, Nat. Nanotech. 2008 3, 327

Control Groups: As Received PMMA (PMMA) As Precipitate PMMA (P-PMMA)

0.05 wt% percolation concentration? Too low! 30 oC of Tg increase? Too high!

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Glass Transition Behavior of Graphene/PMMA Nanocomposites

• Glass transition temperature (Tg ) changed obviously even without incorporation of graphene!!

• Coagulation process removed surfactant, which significantly decrease the Tg of PMMA.

The authors did not operate coagulation process for control groups!!

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Tg of Graphene/Polymer Nanocomposites – Physical Blending

Solvent Blending Matrix

Polymer ∆Tg (°C) Filler Technique Filler Load

PVDF[98] 0 TRG DSC 4 wt% PBS[138] 0 CRG DMA 2 wt%

LLDPE[139] 0 EG DMA 20 wt% PVDF[140] 3.5 TRG DMA 0.5 wt% TPU[122] -2 TRG DSC 7 wt%

PαMSAN/PMMA[141] 0 TRG DMA 1 wt%

Rubber[142] 0 GO DSC 10 wt% TPU[143] -5 EG DSC 10 vol% TPU[144] 0 TRG DMA 6 wt% PS[108] 0 CRG DMA 1.94 vol% PI[107] 2.6 γ-ABA-GO DMA 0.4 wt%

PVA[132] -4.5

TRG

DSC

1 wt% PMMA[132] 0.3 0.2 wt%

PEI[132] 0 0.1 wt% TPU[145] 0 TRG DMA 4.4 wt%

Melt Blending PE[146] 0 CRG DMA 2 wt%

PA12[147] 0 CRG DSC 2 wt% PET[148] < 2 TRG DMA 7 wt% PTT[149] 0 TRG DSC 7 wt% PC[111] 0 GO DMA 3 wt% PP[110] 0 GO DMA 5 wt%

GO: Graphene oxide CRG: chemically reduced graphene TRG: thermally reduced graphene EG: Expanded graphite 22

Solvent-Blending: Melt-Blending:

Tg of Graphene/Polymer Nanocomposites – Chemical Blending

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In situ Polymerize monomer in the presence of dispersed graphene

Tg of Graphene/Polymer Nanocomposites – Chemical Blending

In situ Polymerization Matrix Polymer ∆Tg (°C) Filler Technique Filler load

PBI[133] 1.8 Pristine graphene DMA 0.2 wt% NIPAA[134] 0 Pristine graphene DSC 0.13 wt% Epoxy[152] 7 TRG DSC 0.05 wt% PMMA[77] 20 CRG DMA 4 wt% PMMA[128] 9 CRG DMA 1 wt%

PMMA[129] 3 GO

DMA 1 wt% 8 CRG

PMMA[76]

14 GO

DSC

6 wt% 19 DMA 7 AIBN-GO DSC & DMA

Vinyl Ester[155] 7 TRG -- 0.2 phr

PUA[156] 4 GO

DSC 0.5 wt%

3.4 Isocyanate-GO 1 wt% PUA[157] 0 TRG DSC & DMA 0.5 wt% PUA[158] 7 CRG DMA 1 wt% PS[159] 8 PS-modified CRG DSC 2.5 wt%

Commonly Tg change was reported for chemical blending process 24

Tg of Graphene/Polymer Nanocomposites – Aqueous Blending

Aqueous Blending (solvent blending with water as solvent) Matrix Polymer ∆Tg (°C) Filler Technique Filler load

PVA[104] 12 CRG DSC 7.5 wt% PVA[170] 4 CRG DSC 0.5 wt% PVA[105] 14 CRG DSC 3.5 wt% PVA[171] 9 GO DSC 0.72 vol% PVA[172] 4 GO DSC 0.7 wt%

Chitosan[135] 5 GO DSC 1 wt% Gelatin[173] 10 GO DSC 2 wt%

PEO[174] 9 TRG DMA 4 wt%

Commonly Tg change was reported for aqueous blending process

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Tg of Nanocomposites & Polymer Nano-confinement

Mayes A, Nature Materials 2005, 4, 651

Grohens Y et al. Langmuir 1998, 14, 2929

Nanoconfinement & nanocomposites

Tacticity effect of nanoconfinement

Dispersion of TRG/PMMA Nanocomposites

Samples: TRG/syndiotactic-rich-PMMA (a-PMMA) TRG/isotactic-PMMA (i-PMMA) in situ TRG/PMMA

Resistance: (by 11-Probe) Modulus:

Dispersion levels of TRG are similar 27

Af ~200

Tacticity Effect on Tg of TRG/PMMA Nanocomposites

Samples: TRG/a-PMMA TRG/i-PMMA

tanδ [tan(E”/E’)] by DMA of: TRG/a-PMMA i-PMMA

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Tacticity Effect on Tg of TRG/PMMA Nanocomposites

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Interaction Density: i-PMMA > a-PMMA

Interaction Intensity: i-PMMA > a-PMMA

Noro, Matsushita, Lodge Macromolecules 2008, 41, 5839-5844

n(T): number of H-bonds per P2VP block

Process Effect on Tg of TRG/PMMA Nanocomposites

Samples: in situ TRG/PMMA TRG/a-PMMA

tanδ [tan(E”/E’)] by DMA of: TRG/atactic-PMMA in situ TRG/PMMA

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Possible Reactions during in situ Polymerization

~1 % of PMMA covalently grafted on TRG

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Process of separating filler and matrix polymer for in situ system

dissolve in THF filtration

dry rinse Tg by DSC:

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In situ TRG/PMMA nanocomposites film

Process of separating filler and matrix polymer for in situ system

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Finding holes perfectly covered by single-layer GO:

TEM:

AFM:

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Oxygen Effect on Graphene Oxide

Hole size: 2.5µm in diameter

TEM grid

Lee, C. et al Science 2008, 321, 385

Force = (TM Deflection) × (Cantilever Spring Constant)

Atomic structure of single-layer GO:

Force = (TM Deflection) × (Cantilever Spring Constant)

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Mkhoyan, K. A. et al, Nano Letters, 2011, 9, 1058

Bridge (C-O-C) bonds were removed after chemical reduction

Hole size: 2.5µm in diameter

TEM grid

Oxygen Effect on Graphene Oxide

Lee, C. et al Science 2008, 321, 385

Conclusion

In situ Polymerization Melt Blending Solvent Blending

Fast, scalable, green process with massive production

• Mechanical Properties: Elastic modulus increase 100% with 0.5 wt% of graphene

• Thermal Properties: Glass transition temperatures affected by process and tacticity

• Electrical Properties: Surface resistance decrease 1010 times with 1 wt% of graphene

• Techniques used: AFM, Rheometer, DMA, XRD, SAXS, TEM, SEM, XPS, FTIR, GPC, TGA, DSC, universal tensile testing instrument.

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Acknowledgement • Dr. Chris Macosko (CEMS) • Dr. Andre Mkhoyan (CEMS) • Dr. Greg Haugstad • Steven Maslo, Jerry Yeh • Group Members

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