1. M. Arjmand1, M. Mahmoodi2, G. A. Gelves1, S. Park2, U. Sundararaj1
An investigation on electrical and electromagnetic interference shielding properties of flow-induced oriented carbon nanotubes in polycarbonate
M. Arjmand1, M. Mahmoodi2, G. A. Gelves1, S. Park2, U. Sundararaj1
1Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, AB
2Department of Mechanical Engineering, University of Calgary, Calgary, AB
October 2010

2. Conductive Polymer Composites (CPC)
CPCs are made by adding a conductive filler into a polymer matrix.
Carbon nanotube (CNT) special characteristics:
Excellent Electrical Properties
Low Density
High Aspect Ratio

3. CPC Applications
The surface/volume Resistivity defines application: Anti-static Protection Ω.sq-1 Electrostatic Discharge (ESD) Dissipation: Ω.sq-1 Electromagnetic Interference shielding < 10 Ω.sq-1

4. Experimental
The masterbatch (Polycarbonate+15 wt% MWNT) was diluted using a Haake rheomix batch mixer.
The diluted material was ground using a Retsch Brinkmann grinder.
The ground materials were injection-molded into a two cavity dog-bone mold according to ASTM D638. (Barrel Temperature: 300oC, Mold Temperature: 80oC, Holding Pressure: 120 bar, Injection Velocity: 80 mm.s-1).
The ground material were also compression-molded at 5000 Psi for 5 minutes into rectangular samples to be used for EMI SE measurements.
ASTM D638

5. Electrical Resistivity Measurements

6. Sample percolation curve
Percolation concept
Sample percolation curve
Nanocomposite
Structure
Percolation

7. Comparison of percolation curve of compression-molded samples (random distribution) with CNT-aligned injection-molded samples (region 3)
Capacitor
Field Emission
Mechanism
Current Dissipation
Flow Direction

8. Log (ρ)=Log (ρ0)-t*log (V-Vc)
Percolation Theory
Log (ρ)=Log (ρ0)-t*log (V-Vc)
ρ : Composite Volume Resistivity
ρ0: Conductive Filler Volume Resistivity
t: Critical Exponent
V: Filler Volume Fraction
Vc: Filler Critical Volume Fraction
Log (ρ0) Vc t R2
Compression Molding
-1.81
0.0028
2.64
0.984
Region 1
0.0064
2.52
0.9913
Region 2
-0.434
0.0083
2.38
0.9845
Region 3
0.0095
2.10
0.9945

9. Current-Voltage characteristics of compression molded sample and injection-molded sample (region 3)

10. Illustration of the effect of nanotube alignment on the appearance of micrograph of CNT-aligned samples
Flow Direction
Perpendicular to the flow direction
Parallel to the flow direction
Adapted from Pötschke et al. Eur. Polym. J. 2004;40(1):

11. SEM image of compression molded sample and injection-molded samples of Polycarbonate/MWNT(1.5 wt%)
Injection-molded (Parallel to the flow)
Compression-molded
sample
Injection-molded (Perpendicular to the flow)

12. TEM Image of injection-molded sample (region 3) in parallel and perpendicular to the flow direction
Parallel to the flow direction
Perpendicular to the flow direction

13. Electromagnetic Interference (EMI) Shielding
Incident EI
EMI SE Mechanisms:
1- Reflection
2- Absorption
3- Multiple-Reflections
EI-R
Reflected ER
Transmitted ET
SE = 10 . log (Pin/Pout)
Pin: Incident Energy Field
Pout: Transmitted Energy Field

14. EMI SE as a function of MWNT content and shielding plate thickness
Higher CNT Content
More Free Electrons on Surface
Higher Contribution of Reflection to EMI SE
Higher Conductivity & Elect.Permitt.
Higher Contribution of Absorption to EMI SE

15. Contribution of reflection and absorption to EMI SE Effect of MWNT content and shielding material thickness

16. Conclusions
Increasing CNT alignment reduces CNT contacts; consequently, higher percolation threshold and lower critical exponent are observed
Verifying Ohm’s law after percolation showed that the field emission mechanism is much more conspicuous in injection-molded aligned samples than those with random distribution of CNT.
For the samples with random distribution of CNT, shielding by reflection and absorption increased with increase in CNT concentration and in shielding material thickness.

17. Acknowledgements
Thomas Asperley and Michal Okoniewski, Electrical Engineering Department, University of Calgary, Calgary
Dr. Michael Schoel and Dr. Tobias Fürstenhaupt (University of Calgary) for assistance in SEM and TEM images

18. Any Questions?