Young April2010

Polymer Nano-composites

Robert J Young FREng*

School of Materials,

University of Manchester, UK

Collaborators:Carole Cooper, Matthew Halsall, Kostya Novoselov, Kannan Prabakaran, LiboDeng, Steve Eichhorn, Shuang Cui, Ian Kinloch, Paweena Sureeyatanapas

* Also Chair Professor, ITC, Hong Kong Polytechnic University

Contents• Advanced Composites

• Carbon fibres

• Raman spectroscopy

• Carbon nanotubes (SWNTs)

– Raman spectroscopy

• Carbon nanotubes in epoxy composites

– Mechanical deformation

– Interfacial stress transfer

• Nanotube composite nanofibres

• Double Walled carbon nanotubes

• Graphene

Prediction of Advanced Composites Use in USAF Aircraft

Formula 1 Motorsport Major advances have beenmade since the 1970s by

British Companiesthrough the use of

advanced composites with high stiffness and strength

Carbon Fibre Composites

+ Resin =

Carbon Fibres

Composite

WovenFabric

Fibre – Reinforced Composites

WOVEN ARAMID CARBON/EPOXY

Good multi-directional stiffness Good energy absorption

F1 Crash Survival with Composites!

First Commercial Carbon Fibre Composite Aircraft

Maiden flight15th December 2009

Boeing 787

Fibre Reinforcement? – Composite Micromechanics

Stress distribution along a discontinuous fibre

Good bonding

Yielding/debonding

Raman’s Experiment

observer

sunlight(white)

violetfilter

violet

scatteringliquid

Raman-scattered

light

green

green filter

Rayleigh-scattered

lightviolet green

Published 1927Awarded Nobel Prize

Raman spectroscopy

• Inelastic scattering of light• Laser spot size down to 1 μm• Spectra obtained for many non-metallic materials• Particularly useful for nanomaterials• Large stress-induced band shifts (stress sensing!)

specimen

laserbeam

scatteredlight

Raman Spectra of Carbon Fibres

1000 1500 2000 2500 3000

0

100

200

300

P120

P100

P75

P55

P25

Inte

nsity

(Arb

itrar

y U

nits

)

Wavenumber (cm-1)

1000 1500 2000 2500 3000

0

100

200

300

400

T50

HMS4

T650

T800

T40

T300

Inte

nsity

(Arb

itrar

y U

nits

)

Wavenumber (cm-1)

Pitch-Based FibresPAN-Based Fibres

Raman spectroscopy allow the different types of fibres to be characterised

Fibre Modulus

D G G’ G’GD

G’ ≡ 2D

Carbon Fibre Deformation – G’ Band Shift

-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.92630

2635

2640

2645

2650

2655

2660

2665

2670

T50 P100 P120

G' B

and

Ram

an w

aven

umbe

r (cm

-1)

Fibre strain, ef (%)

Rate of strain-induced bands shift proportional to fibre modulus

Composites Micromechanics – Carbon Fibre/Epoxy

T50 carbon fibre in an epoxy resin undergoing deformation

-0.1

0

0.1

0.2

0.3

0.4

0.5

0 500 1000 1500 2000 2500

ef / %

Distance along fibre (μm)

em

= 0.0%

em

= 0.4%

em

= 0.7%

lc/2

Different Forms of Nano-Carbon

NanotubeC60

Graphene

How well do they reinforce a polymer matrix in a composite?

C60 Raman Spectroscopy

500 1000 15005000

10000

15000

20000

25000

30000

35000

273

433

497

710568

773

1101 1250

1468

1574

C60

Rel

ativ

e In

tens

ity (A

rbitr

ary

Uni

ts)

Raman Wavenumber (cm-1)

C60 Particulate Composite

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.01468.6

1468.8

1469.0

1469.2

1469.4

1469.6

Slope = -0.13 cm-1/%

TENSIONC60 in Epoxy Resin

Ram

an W

aven

umbe

r (cm

-1)

Strain (%)1462 1464 1466 1468 1470 1472 1474

10000

20000

30000

40000

TENSIONC60 in Epoxy Resinon PMMA Beam

Strain 0.0% 1.4%

Rel

ativ

e In

tens

ity (A

rbitr

ary

Uni

ts)


C60 Epoxy Composite

He-Ne Laser (633nm red line)

Raman spectrum of HiPco SWNTs

500 1000 1500 2000 2500 3000

G' Band

RBM D Band

G Band

Inte

nsity

/ a.

u.

Raman wavenumber / cm-1

G’ Raman bandStress- and polarization-sensitive

RBM - radial breathing modeBand position ∝ 1/diameter

Deformation of Carbon Nanotubes in Composites

Nanotubes as Fibres

Stress Sensing of Carbon Nanotubes in Composites

2550 2600 2650 2700 2750200

300

400

500

600

700

800

900

1000

0%1.2%

TENSIONSWNT

Rel

ativ

e In

tens

ity (A

rbita

ry U

nits

)


SWNT/Epoxy CompositeThe large stress-induced band shift

implies the nanotubes have a high value of Young’s modulus

Dispersion of 0.1% of SWNTs in a polymeric resin deformed on a beam

Cooper CA, Young RJ, Halsall M. Composites: Part A 2001;32(3-4):401-411.

G’ Band

Band shift under 4-point bending

0,00 0,05 0,10 0,15 0,20 0,252609

2610

2611

2612

2613

2614

2615

2616

y=2615.004 - 15.497 xR=0.99398

Ram

an s

hift

(cm

-1)

% Strain

Nanotube Composite beam

Band-shift rate-15.5 cm-1/% strain

OpticalStrain Gauge

Estimation of Nanotube Modulus

Raman band shift rate can be relatedto modulus by following the shift

of the same G’ Raman bandfor carbon fibres of known modulus

0 100 200 300 400 500 600 700 800 9000

5

10

15

20

25

30

35

40

45

50

Carbon Fibres

P75

P120P100

P55

Ram

an B

and

Shift

Rat

e (c

m-1 /

%)

Tensile Modulus (GPa)

( )S S d2 02 2

2

21= −∫

−πν θ θπ

π

cos sin

( )S S do3 02 22= −∫ sin cos sinθ θ ν θ θ

π

Band shift rate for random 2-D orientation

Band shift rate for random 3-D orientation

where S0 is the measured SWNT shift rate

Cooper CA, Young RJ, Halsall M., Composites: Part A 2001;32(3-4):401-411.

CalculatedModulus

2-D(GPa)

SWNT 780 ±210

204 ± 83MWNT-50 cm-1 %-1/TPa

Individual Carbon Nanotubes

Nanotubes as Molecules

(0,0)

Ch = (10,5)

a2

a1

x

y

Structures of Carbon Nanotubes

http://www.photon.t.u-tokyo.ac.jp/~maruyama/

Unit cell for a (6,3) tube

The tube diameter dt is given by

The chiral angle θ is given by

dt

Geometry of Chirial Single Walled Nanotubes

π/)(246.0 2/122 mnmndt ++=

⎥⎦

⎤⎢⎣

⎡

+= −

)2(3tan 1

nmmθ

AFM image 10×10 μm2

Preparation*

Chemical vapour deposition on a Si Substrate containing nanometer size iron catalyst particles. The Si substrate had been oxidised to have a thin SiO2 surface coating.

The nanotubes nucleate and grow from well-isolated catalyst particles and nanotube bundles are not formed.

*The isolated nanotubes were prepared by Drs N Wilson & J McPherson of University of Warwick following the method of Jurio et al (Phys. Rev. Lett., 86 (2001) 1118)

Individual nanotubes – AFM

Diameter of laser spot ~2 μm

Raman spectra of individual single-walled nanotubes

Laser Polarisation

2 μm

Nanotubes must be in the correct orientation and in resonance

50 100 150 200 250 300 3500

10000

20000

30000

40000

50000

60000

267

226

171

Inte

nsity

(a.u

.)


WeakSiliconBand

(17,2)

(9,7)

(10,3)

Isolated Single-Walled Nanotubes – Breathing Modes

Resonance Raman Scattering – strong RBMs

Nanotube Composite Nanofibres

Kannan P., Eichhorn S.J. and Young R.J.“Deformation of isolated single wall carbon nanotubes in electrospun polymer nanofibres”,

Nanotechology, 18 (2007) 235707

“Debundling, isolation, and identification of carbon nanotubes in electrospun nanofibers”

Small, 4 (2008) 930–933

Electrospinning poly(vinyl alcohol) composite nanofibres

• Rate of flow = 0.08-2 ml/hour

• Voltage = 15-25 kV

• Tip-to-collector distance = 60-120 mm

Conditions:• Polymer – poly(vinyl alcohol)

• Solvent – deionised water

• SWNTs - 0.04%

Electrospun poly(vinyl alcohol) composite nanofibres

• Dilute solution of PVA containing 0.04% SWNTs spun in a strong electric field

• PVA composite nanofibres were produced containing low loadings of SWNTS

TransmissionElectron

Micrograph

Composite nanofibres – Scanning Electron Microscopy

Nanofibre bundle

Isolated nanofibre

500 1000 1500 2000 2500 3000

10000

20000

30000

40000

Isolated nanofibre

Nanofibres

Nanotubes

Inte

nsity

(a.u

.)


(a)

500 1000 1500 2000 2500 3000

4000

6000

8000

10000(b)

200 225 250 275 300

251

Raman Wavenumber (cm-1)2475 2550 2625 2700 2775



Inte

nsity

(a.u

.)

Raman spectra of SWNTs in PVA nanofibres

• Nanotubes are debundled and separated by:- high shear forces - strong electric field

Raman spectra Isolated nanofibre

HeNe laser1.96 eV

Experimental Kataura plot – Identification of SWNT

200 250 300 350

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

EM

11

ES22

ES11

Eii (e

V)

ωRBM (cm-1)

1.96 eV HeNeLaser

Metallic (Raman with tunable laser) – Fantini et al, PRL 93 (2004) 147406Semiconducting (Spectrofluorometric analysis) – Bachilo et al, Science 298 (2002) 2361

(10,3)

RBM

HiPcoNanotubes

Near Infrared Laser 785 nm (1.59 eV)

200 250 300

270

247

234

227

217

204

Inte

nsity

(a.u

.)

Raman Wavenumber (cm-1)200 250 300

270239

234

227 270

239

234227

Inte

nsity

(a.u

.)


Nanotube Debundling and Separation

HiPco bundles Individual Nanofibres

Radial Breathing Modes

Nanofibre Composite Microstructure

• Nanotubes aligned along nanofibre axis• Nanotubes debundled and isolated• Low nanotube volume fraction (only 0.04% by weight)• Only nanotubes in resonance are “seen” in the Raman spectrum

N.B. Not to scale

2 μm laser spot

Deformation of SWNTs in PVA nanofibres

0.0 0.1 0.2 0.3 0.4 0.5

1586

1588

1590

1592

G Band

Ram

an w

aven

umbe

r (cm

-1)

Strain (%)

(a)

0.0 0.1 0.2 0.3 0.4 0.52600

2602

2604

2606

2608

Ram

an w

aven

umbe

r (cm

-1)

Strain (%)

G' Band

(b)

Deform individual nanofibres in tension

Shifts of G and G’ bands demonstrates stress transfer to nanotubes

Young’s Modulus

> 0.8 TPa

Composite Reinforcement by Nanotubes

Summary

• Large shifts of the nanotube G’ band are found under stress

• This indicates reinforcement by the nanotubes

• Larger band shift are found for the SWNTs than MWNTs

• This implies better reinforcement by SWNTs

• How efficient is the stress transfer between the layers in MWNTs?

Double walled carbon nanotubes(DWNTs) may have the answer!

SWNT

Nanotube-polymer interface Wall-wall interface

DWNT MWNT

• Raman spectra of the SWNTs give us the polymer-outer wall interface⇒ We have seen that this interface is effective.

• MWNTs – the contribution from all the layers is not distinguishable.

• DWNTs – Advanced Materials, 21 (2009) 3591

Single, Double and Multi-walled Nanotubes

Preparation of Double Walled Carbon Nanotubes

SWNTs Peapods DWNTs

500°C 1300°C

C60

Formation of ‘Peapods’

High resolution TEM

(GAD Briggs et al, Oxford)

Raman Spectrum of Original SWNTs

2500 2600 2700 2800

2630

Inte

nsity

(a.u

.)

Raman shift (cm-1)

G'

SWNTs

100 200 300 400

146

160

164

178

189

Inte

nsity

(a.u

.)

Raman shift (cm-1)

SWNTs

RBMs G’ Band

Well-defined Raman spectrum – 1.96 eV laser

• Population of different SWNTs > 1.3 nm in diameter

100 200 300 400

152

166175

190

196

256282

288

302

323

345338

356

366

Inte

nsity

(a.u

.)

Raman shift (cm-1)

DWNTs

2500 2600 2700 2800

G'1

DWNTs

2592

2630

Inte

nsity

(a.u

.)

Raman shift (cm-1)

G'2

DWNT Raman Spectrum

RBMs G’ Band

Additional RBMs2nd G’ band

The presence of the inner walls has a major effect on the spectrum

Dresselhaus: Double resonance process is occurring independently in each layer N.B. Wide split due to larger difference in diameters

SWNT G’ Band Shift in Tension and Compression

-1.0 -0.5 0.0 0.5 1.0

-8

-6

-4

-2

0

2

4

6

Tension Compression

ΔG' (

cm-1)

Strain (%)

Slope: -10.5 cm-1/%

Peapods

-1.0 -0.5 0.0 0.5 1.0

-6

-4

-2

0

2

4

6 Tension Compression

ΔG' (

cm-1)

Strain (%)

Slope: -12.7 cm-1/%

SWNTs

• Large band shifts at low strain, -0.5% to +0.5% (Eeffective for SWNT ~ 760 GPa)• Band shift stops when interface fails

SWNTs Peapods

Interface!

Shifts of the G’ Band Components in DWNTs

-1.0 -0.5 0.0 0.5 1.0

-6

-4

-2

0

2

4


ΔG

' 1 (cm

-1)

Strain (%)

Slope: -1.1 cm-1/%DWNTs

-1.0 -0.5 0.0 0.5 1.0

-6

-4

-2

0

2

4


ΔG

' 2 (cm

-1)

Strain (%)

Slope: -9.2 cm-1/%

DWNTs

G’1 G’2

Inner walls Outer walls

• Only the G’ band from the outer wall shifts• Poor stress transfer between inner and outer walls

Prediction of Effective MWNT modulus, Eeff

⎥⎦

⎤⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛−−

+=

T

gT

AAk

EAA

A

E1

0

1

eff

11

)( k – Stress transfer efficiency factorEg -Young’s modulus of grapheneA1 - cross-sectional area of the outermost shell, AT - total area of the MWNT excluding the annulus and A0 - area of the annulus along the centre of the nanotube

L. Zalamea, H. Kim, R.B. Pipes, Comp. Sci. and Tech., 2007, 67, 3425-3433

Shear stress transferbetween the walls

Prediction of Effective Modulus of MWNTs

1 2 3 4 5 6 7 8 9 100.0

0.2

0.4

0.6

0.8

1.0

k=0.4k=0.2

k=0.8

k=0.6

Eef

f/Eg

Number of Walls, n

k=0.0

k=1.0

n = 1,2,3,…..,

EgGraphene Modulus~1 TPa

Stresstransfer

efficiency

DWNTs

Need either small diameter of nanotubes or to cross-link their walls (Peng et al.)

Graphene

Strong resonance Raman spectrum

Collaborators:Kostya NovoselovAndre GeimIan KinlochLei Gong (PhD student)

Single layer identifiedin Manchester

(Novoselov, Geim et al, Science 2004*)

* >2000 citations to date!

Young’ modulus ~ 1000 GPa

Graphene Composites

Graphene: E = 1 TPa, σf = 150 GPa1. Is there good reinforcement from an one atom thick filler when

all atoms in contact with matrix?

2. Does continuum mechanics apply to a one atom thick crystal?

Mechanically-exfoliated Graphene

1500 2000 2500 30000

10000

20000

30000

40000

50000

>5 Layers

3 Layers

1 Layer

Inte

nsity

(a.u

.)


Mechanically-Cleaved Graphene

2 Layers

G'G

Optical micrographRaman spectra

Raman spectroscopy allows the number of layers to be “counted”

Deformation of a Graphene Monolayer

Optical micrographRaman G’ Band Shift

Single layer on the surface of a PMMA beam

2500 2550 2600 2650 2700 2750

Inte

nsity

(a.u

.)

Raman wavenumber (cm-1)

Relaxed

Unloaded

0.7% strain

G' Band

Deformation of a Graphene Monolayer Composite

-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.82610

2615

2620

2625

2630

2635

2640

2645

2650

Loading Unloading

Ram

an w

aven

umbe

r (cm

-1)

Strain (%)

stick/slip

High shift rate implies a high

Young’s modulus for graphene

∼ I TPa

Mapping of Axial Strain across the Graphene Monolayer

0 2 4 6 8 10 120.0

0.1

0.2

0.3

0.4

0.5

0.6

0.4%

Stra

in (%

)

Position, x (μm)

ns = 10

x

y

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡⎟⎠⎞

⎜⎝⎛

−=)cosh(

2cosh1m ns

lxns

eegStrain in graphene where )/ln(

2 m

tTEGn

g

=

Elastic stress transfer

Mapping of Axial Strain down the Graphene Monolayer

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡⎟⎠⎞

⎜⎝⎛

−=)cosh(

2cosh1m ns

lxns

eegStrain in graphene where )/ln(

2 m

tTEGn

g

=

Elastic stress transfer0 5 10 15 20 25 30

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Stra

in (%

)

Position, y (μm)

x

y

Line calculated for ns = 10 at 0.4% strain

Mapping of Axial Strain across the Graphene Monolayer

0 2 4 6 8 10 120.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.6%

Stra

in (%

)

Position, x (μm)

x

y

g

g

tExe i4

dd τ

−=

Interfacial failure at high strain

Interfacial shear stress, τi, given by

τi ∼ 1 MPa

How long does the graphene flake need to be?

0 2 4 6 8 10 120.0

0.1

0.2

0.3

0.4

0.5

0.6

Stra

in (%

)

Position, x (μm)

0.4%

ns = 2090 % of

max strain

0.5 lc = 1.6 μm

lc ~ 3 μm10 lc = 30 μm

• Hence ideally need > 30 micron wide flakes• Solvent exfoliation (e.g. Coleman et al) make flakes only microns in size

Need to make larger flakes or functionalise

Interfacial Shear Stress

0 2 4 6 8 10 12

-6

-4

-2

0

2

4

6 ns = 10, 20, 50

Inte

rfaci

al S

hear

Stre

ss (M

Pa)

Position, x (μm)• Maximum value of τi = 2 MPa• For carbon fibre composites, typically 20 to 30 MPa• Interfacial stress transfer will only be taking place through van der Waals bonding across an atomically smooth surface hence not unsurprising it is low

)2/cosh(

sinh

mfi nslxns

enE⎟⎠⎞

⎜⎝⎛

=τ

Conclusions

• Raman spectroscopy can be used for stress sensing in nanomaterials

• C60 offers little reinforcement in composites

• Carbon nanotubes demonstrate some characteristics similar to small carbon fibres.

• Stress transfer in nanotube composites can be followed from Raman band shifts.

• Spectra can be obtained from isolated nanotubes.

• Electrospinning allows debundling and isolation of nanotubes.

• Double walled nanotubes have poor internal stress transfer.

• Graphene shows Raman features similar to other forms of carbon and the same phenomena can be studied.

Documents

Young April2010