Polypyrrole colloids—assisted proton transport in hydrated polyacrylic acid matrix

Abstract

Abstract This paper reports an investigation into the rheological behavior of aqueous suspension systems consisting of colloidal polypyrrole (PPy) particles and polyacrylic acid (PAA). We have observed a strong interaction between PPy 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 semi-interpenetrating network (semi-IPN) consisting of linear PAA (M.W.=2000) in a cross-linked polymer [poly(acrylamide-methylenebisacrylamide) 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 content, the composites are electrically non-conductive in the dry state. However, they become electrically conductive when hydrated. There is a percolation threshold of water content with respect to the electrical resistivity. The semi-IPN composites containing PPy appear to have a lower percolation threshold 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 enhancement of proton transport by PPy colloids. This enhancement is probably due to the fact that PPy possesses a weak Bronsted basicity as well as a rigid conjugated structure. In other words, nitrogen atoms of PPy may coordinate with protons not too strongly and allow the protons to transport along the planar conjugated structure of PPy, thus contributing to the proton conductivity.