Lowering the percolation threshold of conductive composites using particulate polymer microstructure

The percolation thresholds of carbon black-polymer composites have been suc cessfully lowered using particulate polymer starting materials (i.e., latex and water-dispersible powder). Composites prepared using carbon black (CB) and commercial poly(vinyl acetate) (PVAc) latex exhibit a percolation thre shold near 2.5 vol % CB. This threshold value is significantly lower than t hat of a comparable reference composite made from poly(N-vinylpyrrolidone) (PNVP) solution and the same CB, which exhibits a sharp rise in electrical conductivity near 15 vol % CB. This dramatic difference in critical CB conc entration results from the segregated microstructure induced by the latex d uring composite film formation. Carbon black particles are forced into cond uctive pathways at low concentration because of their inability to occupy v olume already claimed by the much larger latex particles. There appears to be good qualitative agreement between experimental findings and current mod els dealing with conductive behavior of composites with segregated microstr uctures. Lack of quantitative agreement with the models is attributed to th e polydispersity of the polymer particles in the latex. (C) 2001 John Wiley & Sons, Inc.