Conductivity and percolation of nanotube based polymer composites in extensional deformations

Anisotropic conductive particles are ideal fillers to achieve electrical conductivity in polymer composites. Polymer processing is generally associated to the development of flow fields. It has been observed that flow yields an increase in resistivity. This increase is ascribed to the rotation and flow induced alignment of the particles. Indeed alignment lowers the inter-particle contact probability and thereby the conductivity of the material. The effect of laminar shear has been the topic of several studies over the last years. However, the contribution of elongational flow remains vague in spite of its ubiquity in polymer processing. We report an experimental study in which the contribution of elongational flow and extension is isolated. It is found that the resistivity of extruded composites displays a quadratic increase as a function of the draw ratio. A simple model that considers the relative translation of the particles accounts for this behavior and reveals that translation has much more dramatic consequences than rotation on the conductivity and percolation of nanocomposites.