Humidity sensor using gel polyelectrolyte prepared from mutually reactive copolymers

Two mutually reactive three components copolymers were prepared for the humidity sensitive membrane. The major ingredient of humid membrane is gel polyelectrolyte consisting of cross-linked copolymers of vinylbenzyl chloride (VBC)/bis(2-methoxyethyl)itaconate (B-2-MEI)/[2-(methacryloxy)ethyl]trimethyl ammonium chloride (METAC) and 2-(dimethylamino)ethyl methacrylate (DAEMA)/B-2-MEI/METAC=30/10/20, 25/10/25 and 20/10/30. The cross-linked copolymers of VBC/B-2-MEI/METAC=20/10/30 and DAEMA/B-2-MEI/METAC=20/10/30 showed average impedance of 560, 37 and 3.4 kΩ at 30, 60 and 90% RH, respectively. Temperature dependence, frequency dependence and response time were also measured. The temperature dependence between 5 and 45 °C is −0.94 to −0.86% RH/°C and the hysteresis falls on the range of ±2% RH. The humidity sensors using gel polyelectrolyte were quite resistant to water. The humidity-sensing characteristics of the sensor do not change when the sensor was soaked in water after 2 h.