Water resistive humidity sensor composed of interpenetrating polymer networks of hydrophilic and hydrophilic and hydrophobic methacrylate

An interpenetrating polymer network (IPN) film composed of cross-linked 2-hydroxy-3-methyacryl-oxypropyl trimethylammonium chloride (HMPTAC) polymer and cross-linked ethylene glycol dimethacrylate (EGDMA) polymer was formed on a sintered alumina substrate with interdigitated gold electrodes to fabricate a water-resistive humidity sensor. The impedance of the sensor decreased from ca.10/sup 7/ Omega to ca.10/sup 2/ Omega with increasing humidity from 0% RH to 90% RH. In spite of the cross-linking and interpenetrating with the hydrophobic polymer, the sensitivity is almost the same as that of the HMPTAC homopolymer sensor. Little hysteresis was observed. The characteristics of this IPN sensor changed little even after soaking in water for 120 min. This sensor is more water-resistive than other IPN sensors prepared by using melamine resin or HEMA polymer as a second incorporating polymer. It seems that this is due to the good compatibility of HMPTAC and EGDMA.<>