Abstract

Two mutually reactive three component copolymers were synthesized to utilize as humidity-sensitive membranes. The major ingredient of a humid membrane is the cross-linked polyelectrolyte obtained from the copolymers 4-vinylpyridine (VP)–(methacryloxyethyl)trimethylammonium chloride (METAC)–n-butyl acrylate (BA) = 1 ∶ 2 ∶ 1, 2 ∶ 2 ∶ 1, 2 ∶ 3 ∶ 1 and 3 ∶ 2 ∶ 1, and 2-chloroethyl acrylate (CEA)–METAC–BA = 1 ∶ 2 ∶ 1, 2 ∶ 2 ∶ 1, 2 ∶ 3 ∶ 1 and 3 ∶ 2 ∶ 1. The humidity sensor prepared from the reaction of VP–METAC–BA = 3 ∶ 2 ∶ 1 with CEA–METAC–BA = 3 ∶ 2 ∶ 1 showed average impedance of 620, 41.9 and 3.38 kΩ at 30, 60 and 90% relative humidity humidity (RH), respectively. Temperature dependence, frequency dependence and response time were measured. The variation of humidity on temperature between 5 and 35 °C was −0.62 to −0.67% RH °C⁻¹ and the hygrometric hysteresis between humidification and desiccation processes were less than ±2% RH. The humidity sensors using polyelectrolyte cross-linked were quite resistant to water.