Polymeric humidity sensor using organic/inorganic hybrid polyelectrolytes

Thin film humidity sensors were prepared using inorganic/organic hybrid polyelectrolytes, which were prepared from the sol-gel reaction of copolymers of [2-(methacryloyloxy)ethyl]dimethyl propyl ammonium bromide (MEDPAB), n-butyl methacrylate (BMA) and 3-(trimethoxysilyl)propyl methacrylate (TMSPM) with colloidal silica. The humidity-sensitive polyelectrolytes were composed of copolymers with different contents of MEDPAB/BMA/TMSPM = 60/30/10, 55/30/15 and 50/30/20. It was found that the resistance varied according to the content of MEDPAB and colloidal silica. The resistance ranged from 107 to 103 Ω between 20% and 95% RH, which was required for a humidity sensor operating at ambient humidity. The characteristics of humidity sensor, such as hysteresis, response time, temperature dependency, frequency dependency, water durability and long-term stability were further studied.