M. Arjmand1, M. Mahmoodi2, S. Park2, U. Sundararaj1. An Investigation on Electrical and Electromagnetic Interference Shielding Properties of Flow-induced Oriented Carbon Nanotube in Polycarbonate M. Arjmand1, M. Mahmoodi2, S. Park2, U. Sundararaj1. 1Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, AB 2Department of Mechanical and Manufacturing Engineering, University of Calgary, Calgary, AB PPS-27 May 2011

CPCs’ Structure 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 Corrosion Resistance

CPC Applications The surface/volume Resistivity defines application: Anti-static Protection 1010-1012 Ω.sq-1 Electrostatic Discharge Dissipation (ESD) 104-108 Ω.sq-1 Electromagnetic Interference shielding < 10 Ω.sq-1

Polystyrene Masterbatch 20 wt% Blending with twin-screw extruder Experimental Injection Molding Polystyrene Masterbatch 20 wt% Blending with twin-screw extruder Pure Polystyrene Compression Molding

Designed Mold Employed in Injection Molding Cavity 2 Cavity 1 Cavity 3

Experimental Design C1: Mold Temperature C2: Melt Temperature C3: Injection/Holding Pressure C4: Injection Velocity Factors Levels C4(mm/sec) C3 (bar) ( C°) C2 ( C°) C1 240 100 60 + 24 215 25 _

Volume Resistivity of 5.0 wt% MWCNT/PS Composite in Thickness Direction There is a direct relation between composite volume resistivity and MWCNT alignment.

Raman spectroscopy ratio parallel/perpendicular Raman Spectrocopy Raman spectroscopy ratio parallel/perpendicular Dװ/D┴ G װ/G┴ Compression molding 1.01 PC #10 1.53 1.44 PC #12 1.35 1.27 PC #14 1.66 1.51

Compression Molded Percolation Curve Percolation Concept Nanocomposite Structure Compression Molded Percolation Curve Percolation 1

Injection Molded Samples’ Percolation Curve Current Dissipation Flow Direction

Injection Molded Sample Compression Molded Sample Illustration of the effect of nanotube alignment on the appearance of micrograph of CNT-aligned samples Injection Molded Sample Compression Molded Sample Flow Direction Parallel to the flow direction Perpendicular to the flow direction Adapted from Pötschke et al. Eur. Polym. J. 2004;40(1):137-148.

TEM Micrograph of 5.0 wt% MWCNT/PS Composite Injection Molded Sample (Parallel to the Flow) Compression Molded Sample

Electromagnetic Interference (EMI) Shielding

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

The relation between conductivity and EMI SE Many researchers believe that there is a direct relation between conductivity and EMI SE. However, there is no scientific criterion to prove the mentioned claim since conductivity needs connectivity while EMI SE does not.

Volume Resistivity and EMI SE

The difference in connectivity of MWCNTs in compression molded and injection molded samples plays the key role in interpretation of the reflection and absorption mechanisms.

Shielding by Reflection and Volume Resistivity The shielding by reflection is related to amount of mobile charge carriers on the shield’s surface and has nothing to do with composite’s conductivity.

Shielding by Absorption There is a direct relation between shielding by absorption and MWCNT connectivity, however, the relation between absorption and composite’s conductivity is not always right.

Greater shielding by absorption in compression molded samples than injection molded ones can be related to higher imaginary permittivity (Electric loss), real permittivity (Electric dipole formation) and magnetic permeability (magnetic dipole formation) in compression molded (randomly distributed MWCNT) samples.

Conclusions The conductive polymer composites showed lower electrical conductivity at greater MWCNT alignments which is ascribed to decrease in likelihood of MWCNT contacting each other at higher MWCNT alignments. Increase in reflection by increase in MWCNT concentration is due to increase in amount of mobile charges and has nothing to do with CPCs’ electrical conductivity. Absorption increases with decrease in MWCNT alignment which is due to higher real (electric dipole) and imaginary (electric loss) permittivity and magnetic permeability (magnetic dipole) at lower MWCNT alignments. To achieve higher electrical properties, the injection molding process should be designed in such a way to approach the MWCNT random distribution.

Acknowledgements Natural Sciences and Engineering Research Council of Canada (NSERC). Thomas Apperley and Pr. Michal Okoniewski, Electrical Engineering Department, University of Calgary, Calgary, Canada for assistance with Electrical properties measurements. Mr. Wei Xiang Dong and Dr. Tobias Fürstenhaupt for preparation of TEM specimens by ultramicrotoming. Dr. Samaneh Abbasi of Ecole Polytechnique (Montreal, Canada) for assistance with Raman spectroscopy. Polymer Processing Society PPS-26 Organizing Committee Graduate Travel Award. SSAF Travel Grant from Schulich School of Engineering, University of Calgary.

Any Questions? marjmand@ucalgary.ca u.sundararaj@ucalgary.ca