Humidity sensing and electrical properties of hybrid films prepared from [3-(methacrylamino)propyl] trimethyl ammonium chloride, aqueous monodispersed colloidal silica and methyl methacrylate

Humidity-sensitive hybrid films were synthesized from [3-(methacrylamino)propyl] trimethyl ammonium chloride (MAPTAC), aqueous monodispersed colloidal silica with a coupling agent of 3-(trimethoxysilyl)propyl methacrylate (MSMA), and methyl methacrylate (MMA). The thin film material was subjected to infrared analysis. Subsequently, its humidity sensing characteristics and the sensing mechanism were investigated by measuring the complex impedance spectra of the sensor at different humidity levels. The capacity tolerance to high humidity atmosphere, sensitivity and linearity of pure poly-MAPTAC film was increased by addition of MSMA–SiO2 and MMA. The complex impedance spectra and composition were used to explain the increase in sensitivity and linearity of the poly-MAPTAC added with MSMA–SiO2 and MMA. The characteristics of the humidity sensor, such as tolerance to high humidity atmosphere (97% RH) and chemical environment (20% C2H5OH vapor), sensitivity, linearity, hysteresis, response time, temperature dependency, frequency dependency and long-term stability, were further studied. The activation energy for conduction reduced with water adsorption.