Humidity sensing and electrical properties of a composite material of SiO2 and poly-[3-(methacrylamino)propyl] trimethyl ammonium chloride

In this present work, humidity sensors were prepared using in situ synthesized composite of hydrolytic tetraethyl orthosilicate (TEOS) and poly-[3-(methacrylamino)propyl] trimethyl ammonium chloride (poly-MAPTAC). The infrared spectra of the material were analyzed, the humidity sensing and electrical properties of the sensor were investigated by measuring the complex impedance spectra at different humidities. The sensor based on composite film showed better sensing properties than poly-MAPTAC film, such as satisfactory resistance to high humidity atmosphere (97% RH) and chemical environment (20% C2H5OH vapor), high sensitivity (three orders), better linearity over humidity range (10-90% RH), negligible hysteresis and quicker response and recovery (humidification: 60 s, desiccation: 120 s). The sensor's linearity depended on the applied frequency. The temperature influence between 15 and 35 °C; found to be −0.11 and −0.05% RH/°C at 10 and 90% RH, respectively. The activation energy for conduction reduced with water adsorption. The different impedance plots observed at low and high relative humidity suggested different sensing mechanisms of poly-MAPTAC/SiO2 composite material.