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

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

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

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

Electrical Resistivity Measurements

Sample percolation curve Percolation concept Sample percolation curve Nanocomposite Structure Percolation

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

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 -0.6842 0.0064 2.52 0.9913 Region 2 -0.434 0.0083 2.38 0.9845 Region 3 +0.3035 0.0095 2.10 0.9945

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

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):137-148.

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)

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

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

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

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

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.

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

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