The effect of pH and temperature on the electrical conductivity of membranes made of methacrylic acid copolymers

Abstract

The specific resistance was measured of swollen homogeneous and heterogeneous ion-exchange membranes made of methacrylic acid copolymers with N-(2-hydroxypropyl)methacrylamide and of its copolymers with 2-hydroxyethyl methacrylate. In the case of copolymers of 2-hydroxyethyl methacrylate and methacrylic acid, an increase in the methacrylic acid content raises the specific resistance of the membrane if the carboxylic groups are not ionized. At the degree of neutralization 0.5 the dependence becomes a reverse one. In copolymers of N-(2-hydroxypropyl)methacrylamide with 50 and more per cent of methacrylic acid the specific resistance of the membrane increases with increasing content of methacrylic acid in the case of the nonionized form while remaining virtually unchanged in the ionized form. All the investigated copolymers of N-(2-hydroxypropyl)methacrylamide have a maximum on the curve describing the dependence of the specific resistance on pH. This pH coincides with pH at which the diffusion mobility of the charge carrier of Na+ is highest. The dependence of the specific resistance on temperature can be described in terms of an empirical equation ρT = ρ0e-bT.