Preparation And Properties Of Humidity-sensitive Material Based On Several Modified Polyelectrolytes

In recent years, humidity measurement and monitoring have been widely used in industrial and agricultural production, environmental monitoring and protection, meteorology, food storage and science, etc. Studies on materials used for humidity sensor are increasing. Among them, polymer electrolytes received most attentions due to the advantages of ease of preparation, low cost, quick response and high sensitivity, etc. However, they also exhibit the shortcomings of large hysteresis, instability at high humidity, unsatisfactory long-term stability and so on. To overcome these shortcomings, polyelectrolytes were usually modified by copolymerizing, grafting, crosslinking, preparing organic/inorganic composites and formation of interpenetrating networks (IPN).Copolymer of [2-(methacryloyloxy)ethyl]dimethyl butyl ammonium bromide (MEBA) withγ-methacryloxypropyl trimethoxy silane (KH570)(MEBA-co-KH570) and 2-(diethylamino)ethyl methacrylate(DEAEMA) with n-butyl methacrylate(B -MA) (DEAEMA-co-BMA) were prepared by radical copolymerization, and humidity sensors based on ordered TiO₂ porous film and sodium polystyrenesulfon ate (NaPSS) were prepared by template method.Resistive-type thin film humidity sensors were prepared using the copolymer of MEBA-co-KH570 as humidity-sensitive material, and the effects of quaternization time, concentrations of polymer on humidity-sensitive properties of the humidity sensors were examined. The copolymer of MEBA-co-KH570 was modified by doping with inorganic salts of LiCl, CaCl2 and FeCl3. The effects of type of doped inorganic salts, doped-concentrations of salt on humidity-sensitive properties of the humidity sensors were investigated. The effects of doping of inorganic salts on humidity- sensitive properties were also examined by complex impedance analysis. It was found that humidity sensor exhibited a high sensitivity and good linearity (R=-0.9948) under the optimum concentration of the copolymers (10mg/ml), and the impedance of sensors decreased with longer quaternization time and increasing concentration of polymer; In addition, doped salts of LiCl and CaCl2 caused the impedance of sensor more small, but doped salt of FeCl3 exhibited a different behavior; The optimum doped-concentration of LiCl was 10-5mol/ml.Simultaneously crosslinked and quaternized DEAEMA-co-BMA copolymer in saturated vapor of 1, 4-dibrombutane was prepared as a humidity-sensitive material of sensor. The effects of crosslinking and quaternization time, organic solvent on humidity-sensitive properties of sensors were examined. Surface morphology of the sensors, response time and long-term stability at different vapor environments were also measured and estimated. The experimental results showed that humidity sensors have the advantages of good linearity, high sensitively, satisfactory long-term stability and durability to organic solvent of acetone, etc.Humidity sensors based on ordered TiO₂ porous film and sodium polystyrenesulfonate (NaPSS) were prepared by template method. Surface morphologies of the sensors were observed by scanning electron microscope (SEM), and the humidity-sensitive properties of sensors have been investigated. The results showed that the humidity sensor based on the TiO₂ porous film and NaPSS has high sensitivity, quick response-recovery time, and a very small hysteresis loop than the pure polymer NaPSS humidity sensor.