| In this paper, two novel polyelectrolyte copolymers — poly(MEBA-co-KH570) and poly(MEBA-co-DMAEM-co-KH570) were prepared by radical copolymerization of [2-(methacryloyloxy)ethyl]dimethyl butyl ammonium bromide (MEBA), dimethylaminoethyl methacrylate (DMAEM) and y-methacryloxypropyl trimethoxy silane (KH570), respectively.Resistive type thin film humidity sensors were prepared using the two polyelectrolyte copolymers as humidity-sensitive materials. The effects of composition of the copolymers, technical parameters for sensor fabrication, electrode structure, protective film and doping agents, etc. on humidity response and water-durability of the humidity sensors have been investigated.The humidity sensors based on the MEBA-CO-KH570 copolymer prepared with a monomer mole ratio of MEBA/KH570=4/l exhibit the best response characteristics: good linearity, high sensitivity, quick response, small hysteresis and good water-durability. Furthermore, the effects of different protective films on water-durability of humidity sensors were investigated.The humidity sensors based on composites of MEBA-CO-KH570 with carbon nanotubes (CNTs) were also prepared, and the humidity sensitive properties of the sensors have been investigated. The sensors exhibit better linearity, especially lower impedance at low humidities.Simultaneously cross-linked and quaternized MEBA-co-DMAEM-co-KH570 copolymer was also investigated as a humidity sensitive material with interpenetrating network (IPN). The humidity sensors based on the MEBA-co-DMAEM-co-KH570 copolymer prepared with a monomer mole ratio of TDMAEM(MEBA+MAEM)/KH570=2/land MEBA/DMAEM=2/1 exhibit the better humidity sensitive properties such as good linearity, high sensitivity, quick response (about 4s), small hysteresis (=1%RH) and good stability at highhumidity (88-93%RH) and high temperature (38°C). Over the range of 11%-94%RH, the sensors exhibit a change of three orders of magnitude (4-638 kO) in impedance that is well-suited for practical use. |
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