Carbon black filled thermoset with controlled microstructure for electrical applications

Composite thermodurcissable chargé de noir de carbone, à microstructure controlée, pour applications électriques

¹ CERMAV-CNRS, Université Joseph Fourier, BP 53, 38041 Grenoble Cedex 9, France * Present address : Rhodia Recherches CRA-GRM/ARM, 52, rue de la Haie Coq, 93308 Aubervilliers Cedex, France ; lionel.FLANDIN@eu.rhodia.com
² Microelectronic Materials Section, Technical University Hamburg-Harburg, D-21071 Hamburg, Germany
³ Polymer/Composites Section, Technical University Hamburg-Harburg, D-21071 Hamburg, Germany
⁴ Groupe de Métallurgie Physique et Physique des Matériaux, UMR CNRS 5510, INSA, 69621 Villeurbanne Cedex, France

Abstract

This paper describes recent developments in carbon-black epoxy composites. Firstly it is observed that AC and electrical properties versus volume fraction of carbon black are in manifest disagreement with predictions of the statistical percolation theory both for real and imaginary parts of the conductivity. They exhibited, in particular, an abrupt variation at a very low fraction of carbon black. The onset of conduction in these composites arose from an precipitous clustering of the conductive particles rather than a “conventional” percolation transition in random insulator-conductor mixture. A simple model based on electrostatic repulsion between electrically charged carbon black particles accounts qualitatively for this singular insulator to conductor transition. Secondly, it is shown that the final microstructure could be largely modified by application of a static electric field on the composite during the curing. The final conductance of the composites can by this way be customized within several orders of magnitude. In the application point of view this method could directly be used to derive heterogeneous composites with controlled electrical properties from homogeneous compounds.