Static and dynamic electrical breakdown in conducting filled-polymers

The electrical resistance of a percolating medium- made of A polymer filled with conductive particles may undergo a steep increase over a narrow temperature range above room temperature. A likely mechanism for the effect is the loss of interparticle contact inducing a weakening of the connectivity of the medium as temperature is increased. When Joule heating is used, the sample behavior depends strongly on whether a tension or current source is used. We show that in the first case, at any value of the voltage drop across the sample, a stable state is reached; on the contrary when a convenient exciting current is used, the sample resistance may diverge spontaneously with time. We demonstrate that most of these behaviors are compatible with the predictions of a random thermal fuse model.