Resistive humidity sensor using polyelectrolytes based on new-type mutually cross-linkable copolymers

Two mutually cross-linkable two kinds of copolymers were prepared to use as humidity-sensitive membranes. The humidity-sensitive thin films consist of cross-linked polyelectrolytes of the following component: 4-vinylbenzyl dimethyl 2-(dimethylamino)ethyl ammonium chloride (1)/2-methacryloxyethyl trimethyl ammonium chloride (2)/2-ethoxyethyl acrylate (3)=1/2/1, 2/2/1, 2/3/1 and 3/2/1 and 4-vinylbenzyl chloride (4)/2-methacryloxyethyl trimethyl ammonium chloride (2)/2-ethoxyethyl acrylate (3)=1/2/1, 2/2/1, 2/3/1 and 3/2/1. The humidity sensor prepared from the reaction of 1/2/3=2/3/1 with 4/2/3=2/3/1 showed an average impedance of 755, 38.5 and 2.52 kΩ at 30, 60 and 90% RH, respectively. Temperature dependence, frequency dependence and response time were measured and the reliability test such as water durability, humidity cycling test and long-term stability were also estimated.