AbstractPercolation conductance has been studied for polypropylene/poly(acrylic acid) membranes (PP‐g‐PAA) prepared by volume grafting of an ionic component onto polypropylene foil. In these membranes the volume fraction of the conducting phase decreases from the surface to the center, brining some anisotropy into the composition. For this material, the “insulator‐ to‐conductor” transition proceeds at a critical volume fractionVcequal to 0.395. It has been proved that this critical volume fraction and the critical exponentt, found to be below that predicted by theory, i.e., 1.2 ± 0.03 instead of 1.6 ± 0.2, result from the gradient in the distribution of the conducting component in the direction of the current flow. Computations ofVcandtfor the same PP‐g‐PAA copolymer with a randomly distributed conducting component have led toVc= 0.08 andt*= 1.53. A critical exponenttin that range is characteristic of three‐dimensional systems; however,Vcis rather low, suggesting a nonspherical shape for the
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