In situ copolymerization of copolymer of methyl methacrylate and [3-(methacrylamino)propyl] trimethyl ammonium chloride on an alumina substrate for humidity sensing

Humidity sensors were fabricated through in situ copolymerization of methyl methacrylate (MMA) and [3-(methacrylamino)propyl] trimethyl ammonium chloride (MAPTAC) copolymer on an alumina substrate. Humidity sensing and electrical properties of the sensor were investigated by measuring the complex impedance spectra. Subsequently the thin film material was subjected to infrared analysis. Batch wise reproducibility and repeatability for this humidity sensor (10-90% RH) were 0.35-1.32 and 0.19-0.64%, respectively. The copolymerized sensor film showed better sensing properties than poly-MAPTAC film, such as negligible hysteresis, fast response time, long-term stability (minimum of 62 days) and satisfactory resistance to high humidity atmosphere (97% RH). The sensor's linearity is dependent on the applied frequency. On an average −0.28% RH/°C for 10-90% RH humidity range was observed for the temperature range 15-35 °C. The improved linearity of poly-MMA/MAPTAC copolymer material was explained by the obtained impedance plot observed. The activation energy for conduction reduced with water adsorption.