Polymeric humidity sensor using polyelectrolytes derived from alkoxysilane cross-linker

Abstract

New reactive amine-containing polyelectrolytes were prepared for the humidity-sensitive membranes. The copolymers were mixed with 3-chloropropyl trialkoxysilane and simultaneously fabricated on the sensor electrode by the cross-linking reaction of both halide and alkoxysilane group. The copolymers were composed of different contents of vinylbenzyltributylphosphonium chloride (VTBPC), [2-(methacryloyloxy)ethyl]trimethyl ammonium chloride (METAC), 2-ethylhexylacrylate (2-EHA) and 4-vinylpyridine (4-VP) (VTBPC/METAC/2-EHA/VP = 2/2/2/4, 3/2/2/3, 2/2/3/3 and 2/3/2/3). And trialkoxysilyl group-containing polyelectrolytes were prepared by copolymerization of [2-(methacryloyloxy)ethyl]dimethyl propyl ammonium bromide (MEDPAB) with 3-(trimethoxysilyl)propyl methacrylate (TSPM). When the resistance dependences on the relative humidity of the copolymers were measured, it was found that the resistance decreased with an increase in the content of VTBPC and METAC. The resistance varied three-orders of magnitude between 20% RH and 95% RH, which was required for a humidity sensor operating at ambient humidity. Temperature dependence, hysteresis, response time, water durability and long-term stabilities under various environments were also measured.