Percolation transition and hydrostatic piezoresistance for carbon black filled poly(methylvinylsilioxane) vulcanizates

The percolation transition and the hydrostatic piezoresistance for carbon black (CB) filled poly(methylvinylsilioxane) vulcanizates were studied as a function of CB volume fraction. A revised tunneling-percolation model based on the method of "subcritical networks" was proposed, which can not only account for the apparent nonuniversal percolation, but also figure out the contribution of changing tunneling current to the hydrostatic piezoresistance. Although there is a general tendency that the relative contribution of tunneling current increases with increasing filler concentration, it is always the variation of effective filler volume fraction which dominates the hydrostatic piezoresistance for the present system, due to the rather limited mobility of the mediating polymer layer between neighboring CB aggregates. The pressure and concentration dependences of the hydrostatic piezoresistance were interpreted in terms of the connectivity and/or the fractal nature of the percolation network. The concentration dependence of hydrostatic piezoresistance could even be associated with the strength of filler-matrix interaction. The baseline drift and poor reproducibility of hydrostatic piezoresistance were ascribed to the residual compressive strain of the rubber matrix, which could not be completely eliminated but could be deducted from the piezoresistance by a novel resistance baseline removal method. (C) 2008 Elsevier Ltd. All rights reserved.