Abstract
An electrical resistance type humidity sensor using ionic copolymers has been studied. A humidity sensitive layer of copolymer film was placed on a pair of combshaped electrodes on a ceramic plate. The ionic copolymers were synthesized from ionic and nonionic monomers in aqueous media.
The electrical resistance of ionic copolymers depended significantly not only on relative humidity, but also on mole fraction of ionic monomer to nonionic monomer. The resistances decreased exponentially with an increase in relative humidity, and they increased with decreasing of mole fraction of ionic monomer in copolymers.
In the sorption process, the humidity sensor responded quicker than in the desorption process. The difference of response in the desorption process remarkably depended on the kind of the copolymers. The response became quicker according to the order shown by hydrophobicity of ionic monomers used. Its cause is analyzed that the diffusion coefficient of water became larger. as loosing the bind between the water molecules adsorbed by copolymers and ionic groups.
The humidity-resistance characteristics of the sensor changed when it was exposed to high temperature atmosphere. The life time of the sensors depended significantly on the kind of ionic copolymers and temperature. The life time decreased exponentially with temperature rise.
