Humidity sensor based on alkali salts of poly(2-acrylamido-2-methylpropane sulfonic acid)

Abstract Poly(2-acrylamido-2-methylpropane sulfonic acid), AMPS, and its alkali salts were prepared. The impedances of these polymers were measured at various humidities and temperatures in the frequency range of 100–1 MHz. The results suggest that in the films of the alkali salts of poly(AMPS) containing 1–2 water molecules per AMPS monomer unit in the low and medium humidity ranges, the majority carrier is the alkali cations. For practical use, a humidity sensor, which is completely water-resistive, was prepared by forming an interpenetrating polymer network composed of a copolymer containing AMPS and hydrophobic poly(ethylene glycol dimethacrylate).