polymer Nanocomposites and Electrical Conductivity

8/20/2019 polymer Nanocomposites and Electrical Conductivity

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MAT706

Advanced Structure-PropertiesRelationship in Materials

10 – Electrical Conductivity in Polymer Nanocomposites

Emiliano Bilotti

[email protected]

mailto:[email protected]:[email protected]


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MAT706

Organiser:Dr Asa H. Barber

Reader in Materials

Deputy Organiser:Dr Emiliano Bilotti

Lecturer in Materials

Contact: [email protected]

Room E403, Engineering Building

Phone: 020-7882-7575

mailto:[email protected]:[email protected]


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Topic Lecturer Week Date

Introduction Asa Barber 1 24 Sept

Practical Asa Barber 2 1 Oct

Practical Asa Barber 3 8 Oct

Nanomaterials Asa Barber 4 15 Oct

Nanocomposites Asa Barber 5 22 Oct

Nanocomposites Asa Barber 6 29 Oct

Biological nanomaterials Asa Barber 8 12 Nov

Polymer Nanocomposites and

Electrical Conductivity

Emiliano Bilotti 9 19 Nov

Polymer NanocompositesThermal Properties

Emiliano Bilotti 10 26 Nov

Polymer Nanocomposites and

other Functional Properties

Emiliano Bilotti 11 3 Dec

Revision Asa /Emiliano 12 10 Dec

op cs


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L

A

Ammeter Battery

Voltmeter

Variable Resistor

e-=1.6·10-19 C

R=V/I=[Ω]

ρ=RA/L=[Ωm] σ=1/ρ=[Sm-1]

V=I·R=[V]


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R e l a t i v e

E n e r g y

Filled stated

Filled Band Filled

Valence

Band

Empty stated

Band gap

Empty Band

Empty Band

Ef Band gap

Empty

Conduction

Band

Filled

Valence

Band

Band gap

Empty

Conduction

Band

MetalMetal Insulator Semi-Conductor

Metallic bond Covalent or ionic bond


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109

106

103

100

10-3

10-6

10-9

10-12


Al

CuAu

Nylon

Polymers

Metals

Semiconductors

CNT

Carbon

Si

C o n d u c t i v i t y , σ [ S m - 1 ]


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How to provide electrical conductivity to a (electrical insulating) polymer?

By addition of electrical conductive particles -> Polymer composites

How many particles we need to add to the polymer?

Electrical Conductive Polymer/(nano)-

Composites

El i l C d i P l /( )


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Electrical Conductive Polymer/(nano)-

Composites

Note the sudden increase of conductivity in correspondence of

a critical concentration, called percolation threshold

Importance of aspect ratio of conductive particle!

The percolation threshold for CNTs is typically well below 1 wt%!

• Conductive fillers: different carbon fillers


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Rule of Mixture Vs Percolation

Phenomena

C o m p o s i t e Y o u n

g ’ s M o d u l u s

E c ( G P

a )

Mechanical Properties Electrical Conductivity Properties

Rule of Mixture Percolation Phenomena

Please note:

The scale of variation of the physical Properties

The shape of the curve (Linear Vs Exponential)

The amount of filler needed to reach maximum

Filler vol. %

~1

~600

PP/MWNT

0 100


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Percolation – Intuitive Concept


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Percolation of Conductive Particles

Formation of nanofiller-based network

via particle-particle interactions

Courtesy of Prof. G.-F. Gerard, INSA, Lyon


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Double Percolation

Single Percolation

Double Percolation

A

B

A

B

A

Phase A

Phase BCNT


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Percolation Theory

1E-3 0.01 0.1 1 1010

-5

10-4

10-3

10-2

10-1

100

101

102

103

104

m a x [

S m - 1 ]

Percolation Threshold, p c [wt.%]

Low viscosity High Viscosity

Sandler et al. Polymer 2003

Yu et al. NanoLetter 2008

Thakre et al. JAPS 2010

0 1 2 3 4 5 6 7 8 9 10

1E-6

1E-5

1E-4

1E-3

0.01

0.1

1

10

C o n d u

c t i v i t y [ S m - 1 ]

CNT Vol.% [-]

pc

NO!

σmax

Are the values of pc and σ max fixed for a given system?

Polymer/CNT

Why?


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Dynamic Percolation

0 50 100 150 200 25010

-12

10-10

10-8

10-6

10-4

10-2

100

102

5% CNT

3% CNT

2% CNT

1% CNT

( S m - 1 )

T (oC)

CNT weight fraction

0 4 810

-5

10-4

10-3

10-2

10-1

100

0 1 2 3 4

50

100

150

200

T

( o C )

t (106 ms)

172oC

180oC

190oC

( S m

- 1 )

t (ms 106)

172oC

180oC

190oC

(a)

T scan tests Isothermal tests

E. Bilotti, et al. J. Mater. Chem., 2010

The principal way to study the dynamic (or kinetic) percolation is via time-dependent tests

What is the reason for this increase?...


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Dynamic Percolation

CNT re-aggregation - Dynamic Process:

Importance of viscosity of the host polymer!

…CNT re-aggregation!

Poor dispersion Perfect dispersion -Not percolated

Optimal dispersion -Percolated

The classic statistic Percolation Theory assumes random dispersion of conductive

particles in an insulating matrix

In reality the dispersion of nanoparticles, like CNT, is non-ideal and it can vary in time

if sufficient energy is given to the system

Poor mechanical

properties and electrical

conductivity

Good mechanical

properties

Poor electrical conductivity

Good electrical conductivity


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Controlling Dynamic Percolation

2 3 4 5 6 710

-5

10-4

10-3

10-2

10-1

100

3% CNT

C o n d u c t i v i t y [ S m

- 1 ]

Chill Roll speed [m min-1]

220 C

200 210 220 230 2400.01

0.1

1

10

( S

/ m )

T (oC)

5 wt.% CNT

3 wt.% CNT

(diluted from 5 wt. MB)

Example: Melt spinning of TPU / MWNT monofilaments

die

• Conductivity ↑ increases

with the die temperature

• Conductivity ↓ decreases

with the chill roll speed

How to make use of the CNT re-aggregation to get larger electrical conductivity

in real manufacturing processes?


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0 1 2 3 4 510

-12

10-10

10-8

10-6

10-4

10-2

100

102

260oC

220oC

200oC

240oC

( S / m )

CNT weight Fraction ( wt.%)

CNT composite film

Composite Strand @ 210


Melt spun fibre @ various T

0 1 2 3 4 510

-12

10-10

10-8

10-6

10-4

10-2

100

102

260oC

220oC

200oC

240oC

( S / m )

CNT weight Fraction ( wt.%)

CNT composite film



Melt spun fibre @ various T

Example: Melt spinning of TPU / MWNT monofilaments

By fine-tuning the processing conditions it is possible to control the dynamic percolation

process of CNT within a thermoplastic polymer and optimise the electrical conductivity


C lli D i P l i


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10-1

100

101

102

103

104

105

2.10 2.15 2.20 2.25

103

104

105

n 0

( P a s )

T -1 (K

-1 10

3)

n 0 (

P a s )

ang. Freq. (rad s

-1

)

172oC

182oC

190oC

200oC

CNT re-aggregationHypothesis: It is an energy activated process -> regulated by an Arrhenius-type law

ΔE = 249 kJ mol-1

)exp(0 RT

E c

The energy barrier for CNT re-aggregation

is supposed to be the same as the one

relative to the pure polymer viscosity

In analogy with the time-temperature superposition principle it is

possible to impose a conductivity-time superposition principle.



C t lli D i P l ti


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Assumption:

Conductive network formation is (or is limited by) a first order

thermally activated phenomenon.

and by substituting eqn (1):


where ΔtT is the time required for a certain change in

conductivity, Δσ to take place at a temperature T, and Δt’T*is the time needed for the same change to take place at a

different temperature

101

103

105

107

109

10-6

10-4

10-2

100

102

( S

m - 1 )

t' (ms)

172oC

180oC

190oC

T scan

In analogy with the time-temperature superposition:

C t lli D i P l ti


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200 220 240 26010

-4

10-3

10-2

10-1

100

101

( S m

- 1 )

T (oC)

3 wt.%2 wt.%

First Predictive Model for Conductivity of Polymer / CNT melt-spun filaments!




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St i S


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Strain Sensors

0 50000 100000 150000 200000 250000 300000

0

24

6

8

100.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

S t r a i n

( % )

time (ms)

R0=53M

R / R

0

Dynamic Strain Sensitivity of TPU/CNT filaments and derived fabrics

TPU+3%CNT

St i S


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Strain Sensors

http://images.google.co.uk/imgres?imgurl=http://www.cross-fashion.lu/images/marken/northsails.gif&imgrefurl=http://www.cross-fashion.lu/images/marken/?C=S;O=A&usg=__bIAvDqHUef442ZtIUtOGdaAjTUQ=&h=344&w=347&sz=7&hl=en&start=1&um=1&tbnid=PAQjtVe7oovrgM:&tbnh=119&tbnw=120&prev=/images?q=north+sails&hl=en&rlz=1T4ADBF_en-GBGB294NL302&sa=N&um=1


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Self-regulating Heating Compounds

30

Conductive path

filler

ON OFFOvercurrent heating device

Trace Heating Cable


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31

HDPE/ Carbon Nanotubes (CNT)

0.5 1.0 1.5 2.0 2.5 3.0

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

C o n d u c t i v i t y ( S / c m )

Filler Concentration (% V)

CNT

ECNT=1TPa

σCNT=100 GPa

20 40 60 80 100 120 140 160 180

108

10

9

r e s i s t i v i y ( l o g c m )

Temperature (

o

C)

PTC

NT

C


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Vs Vs


Effect of filler size on PTC

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5

0

1

2

3

4

5

6

7

8

100 microns

20 microns

5 microns

P T C

I n t e n s i t y

Ag coated glass (% V)0 4 8 12 16 20 24

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

102

5 microns

20 microns

100 microns

C o n d u c t i

v i t y ( S / c m )

Filler Content (% V)

Flake size


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Hybrid Filler System: CNT + Conductive spheres

+


0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60

102

103

104

105

106

107

108

109

8.37% V Ag coated glass spheres



R e s i s t i v i t y

( c m )

MWNT content (% V)0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60

0.4

0.8

1.2

1.6

2.0

2.4

2.8 8.37% V Ag coated glass spheres



P T C I

n t e n s i t y

MWNT content (% V)


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HDPEPlastomer

a b

conductive

flakes

Polymer blend: HDPE/Plastomer



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CNT in Biodegradable polymer


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CNT in Biodegradable polymerConductive + Degradation Sensing

Hot plate

At selected immersionperiods, specimenswere removed from thevials, dried untilconstant weight.

+-

Pico-ameter

V-source

Voltmeter

Sample

Computer

(a)

PLA+5%CNT

Biopolymer: PLA

M. Fang et al. Polymer 2013

37


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Graphene


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GrapheneOpportunities and Challenges

Graphene


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WoK Search: “Graphene” + “composite*” WoK Search: “CNT” + “composite*”

GrapheneOpportunities and Challenges


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polymer Nanocomposites and Electrical Conductivity

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