polymer nanocomposites and electrical conductivity
TRANSCRIPT
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MAT706
Advanced Structure-PropertiesRelationship in Materials
10 – Electrical Conductivity in Polymer Nanocomposites
Emiliano Bilotti
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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
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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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Electrical Conductivity
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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Electrical Conductivity
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
Electrical Conductivity
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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Controlling Dynamic Percolation
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
Composite Strand @ 190
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
Composite Strand @ 210
Composite Strand @ 190
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
E. Bilotti, et al. J. Mater. Chem., 2010
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.
Controlling Dynamic Percolation
E. Bilotti, et al. J. Mater. Chem., 2010
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):
Controlling Dynamic Percolation
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!
E. Bilotti, et al. J. Mater. Chem., 2010
Controlling Dynamic Percolation
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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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Self-regulating Heating Compounds
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
Self-regulating Heating Compounds
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
+
Self-regulating Heating Compounds
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
10.86% V Ag coated glass spheres
11.91% 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
10.86% V Ag coated glass spheres
11.91% 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
Self-regulating Heating Compounds
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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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End.