New efficient polyelectrolyte containing zwitterionic sulfobetaine salt for the high sensitive resistive humidity sensor

New sulfobetaine zwitterion-containing copolymers were prepared by the copolymerization of [2-[(methacryloyloxy) ethyl]dimethyl] propyl ammonium bromide (MEPAB)/N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropyl) ammonium (DMMSA) for a humidity-sensitive polyelectrolyte. The poly(MEPAB-co-DMMSA)s with a composition of 10/0, 8/2, 6/4, 4/6, 3/7, 2/8 and 0/10 were used to prepare resistive-type humidity sensors. The electrical properties of poly(MEPAB-co-DMMSA) with different amounts of MEPAB and DMMSA were examined as a function of the relative humidity to determine the contribution of the two salts on the sensing properties (linearity and sensitivity). Resistance of the humidity sensors obtained from the copolymers MEPAB and DMMSA varied from 10(7) to 10(2) Omega between 30%RH and 90%RH, which is suitable for a humidity sensor operating at ambient humidity. The humidity-sensing properties of MEPAB were enhanced by doping with a sulfo-betaine-type salt with a significantly different dissociation constant. The temperature dependence, hysteresis, response time, water durability, and long-term stability at high temperature and humidity were also measured.