A HUMIDITY SENSOR COMPOSED OF INTERPENETRATING - POLYMER NETWORKS OF HYDROPHILIC AND HYDROPHOBIC METHACRYLATE POLYMERS

An interpenetrating polymer network (IPN) film composed of cross-linked 2-hydroxy-3-methacryloxypropyl 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(7) OMEGA to ca. 10(2) OMEGA with increasing relative humidity from 0 to 90% (%RH). In spite of cross-linking and interpenetration with the hydrophobic polymer, the sensitivity to humidity is almost the same as that of an HMPTAC homopolymer sensor. Further, little hysteresis was observed. The characteristics of this IPN sensor changed little even after soaking in water for 120 min. It was found that this sensor is more resistant to water than other IPN sensors which were prepared in our laboratory using melamine resin or 2-hydroxyethyl-methacrylate (HEMA) polymer as a second incorporating polymer as previously reported. It appears that this is due to good compatibility between HMPTAC and EGDMA.