Polypyrrole colloids-assisted proton transport in hydrated polyacrylic acid matrix

This paper reports an investigation into the rheological behavior of aqueou s suspension systems consisting of colloidal polypyrrole (PPy) particles an d polyacrylic acid (PAA). We have observed a strong interaction between PPB colloids and PAA chains in an aqueous medium. Based on this observation, a new polymer composite was prepared, in which PPy colloidal particles were uniformly distributed in a semiinterpenetrating network (semi-IPN) consisti ng of linear PAA (M-w = 2000) in a cross-linked polymer [poly(acrylamide-me thylenebisacrylamide) PAAM-MBAM]. The weight ratio of PPy in the composites was varied in the range of 0.2%-2.3%, and as a result of the low PPy conte nt, the composites are electrically non-conductive in the dry state. Howeve r, they become electrically conductive when hydrated. There is a percolatio n threshold of water content with respect to the electrical resistivity. Th e semi-IPN composites containing PPB appear to have a lower percolation thr eshold than the blank semi-IPN composite. For example, as the water content increases from 14 to 15 wt% the resistivity of semi-IPN embracing 0.8% PPy reduces 10 times, while that of the blank semi-IPN reduces only 1.3 times. The difference in electrical resistivity may be attributed to the enhancem ent of proton transport by PPy colloids. This enhancement is probably due t o the fact that PPy possesses a weak Bronsted basicity as well as a rigid c onjugated structure. Ln other words, nitrogen atoms of PPy may coordinate w ith protons not too strongly and allow the protons to transport along the p lanar conjugated structure of PPy, thus contributing to the proton conducti vity. (C) 1998 Elsevier Science B.V. All rights reserved.