The Design, Preparation, Performance And Application Of Polymeric Humidity Sensitive Materials

Four types of polymer humidity sensitive materials were designed and prepared, including silicon-containing polyelectrolytes,quaternaray ammonium salt polyelectrolytes,pyrrole based polyelectrolytes,and hyperbranched polymer humidity sensitive materials.These materials were synthesized by sol-gel,radical copolymerization,UV irradiation,graft,and in-situ polymerization method,respectively, and characterized by FT-IR,NMR,TGA,TEM,SEM,UV-Vis.Resisitive type humidity sensors were prepared by forming film on the interdigital gold electrodes with dip-coating and electrospinning methods.The humidity sensitive properties of the sensors have been investigated.The effects of the composition,structure and morphology of the sensitive films,preparation techniques on the sensing characteristics of the humidity sensors were discussed.The humidity sensitive mechanisms were explored.The 3-aminopropyltriethoxysilane quaternary ammonium salt(APTS-BB) humidity sensors with cross-linking structure were prepared by sol-gel method.The effect of component of the polymers,concentration of dip-coating solution,type of quaternization reagent,and the preparation techniques(quaternization reaction time, aging and cross-linking time of precursor solution,and electrode structures) on the humidity sensitive properties of sensors have been investigated.The sensors easy prepared(one-pot method) and exhibited high sensitivity(the impedance change from 10³ to 10⁷Ωin the range of 97%-11%RH),good linearity(R²=0.977),small hysteresis (1.1%RH) and last response(adsorption time 30.1s,desorption time 34.8s). Furthermore,it was featured with good durability to high temperature and high humidity, and high resistance to water and solvents.The investigations on the humidity sensitive mechanism by complex impedance spectra revealed that the polymer showed sensing characteristics typical of polyelectrolytes,and ion conductivity in its conduction behavior. Copolymers of quaternary ammonium salt with polyether were prepared by radical copolymerization.The effect of ratio of methyl ether methacrylate/2-(dimethylamino) ethyl methacrylate quaternary ammonium salt(PEGMEMA/DB),doped content of NaClO₄,and type of doped salt on the humidity sensitive properties of sensors were investigated.The sensors prepared exhibited very wide sensitive range(0-97%RH), excellent linearity(R²=0.997),high sensitivity(10⁶-10³Î©),small hysteresis(1.6%RH) and fast response(adsorption time 48.6s,desorption time 23.4s).Furthermore,the sensors maintained high conductivity even at very dry atmosphere,are promising to detect low humidity.Humidity sensors based on cross-linked quaternary ammonium salt were fabricated by UV irradiation method.The effect of ratio of poly[2-(dimethylamino) ethyl methacrylate quaternary ammonium salt]/divinyl benzene(PDB/DVB),type of crosslinking agent,prepolymerization of 2-(dimethylamino) ethyl methacrylate quaternary ammonium salt(DB),and irradiation time on the humidity sensitive properties of sensors were investigated.The sensors prepared exhibited high sensitivity (the impedance change from 10³ to 10⁶Ωin the range of 97%-22%RH),good linearity (R²=0.959),small hysteresis(1%RH) and fast response(adsorption time 9.1s, desorption time 31.7s).The whole manufacture procedure was processed in low temperature(≤60℃) and can be accomplished in an hour.In addition,the sensors exhibited excellent durability against water.Pyrrole based polyelectrolytes(PY-PE) humidity materials were prepared by graft and oxidation polymerization.The effects of concentration of precursor solutions and type of carboxylic salt on the humidity sensitive properties of sensors were investigated. The sensors exhibited an impedance change of 10⁴-10⁶Ωin the range of 97%-0%RH, good linearity R² of 0.988,hysteresis of 4.7%RH and fast response(adsorption time 12.5s,desorption time 15.2s).The sensors maintained conductivity even at very low humidity atmosphere(～0%RH),which are promising to detect low humidity. Furthermore,the difference of sensitive behavior of sensors at low and high humidity atmosphere were investigated,the humidity sensitive mechanisms were explored.The sensor based on PY-PE exhibits both ionic and electronic conduction contributed to its conductivity.The humidity sensitive properties of hyperbranched polyester(H20) whose terminal hydroxyl group was converted to carboxylic salt and quaternary ammonium salt group have been investigated.It was found that the type and number of terminal groups,the hyperbranched structure can affected the humidity sensitive properties of H20 based sensors.The sensor prepared exhibited high sensitivity(the impedance change from 10³ to 10⁶Ωin the range of 97%-11%RH),linearity R² of 0.902,small hysteresis(1%RH) and fast response(adsorption time 9.08s,desorption time 9.46s).Compared with linear polymer humidity sensitive material,hyperbranched humidity sensitive material exhibited lower impedance and wider humidity measurement range.Hyperbranched Polyaniline HBPA was prepared by melt polycondensation.The sensitivity of HBPA can be improved by quaternized with n-butyl bromide or dibromobutane;however its linearity was decrease.Through mixing or grafting CNT into the HBPA can decrease the impedance of the sensors at dry atmosphere and broad its humidity measurement range.The applications of APTS-BB humidity sensor in the water detection of organic solvents have been explored.The humidity sensitive properties of sensors in the solvents with different polarity and water content,and dynamic sensing behaviors were investigated;the humidity sensitive mechanisms were explored.APTS-BH fibre humidity sensors were prepared by electrospining method.The effects of composition of electrospining solution,electrospining time,and electrospining voltage on the humidity sensitive properties of sensors were described.Compared with thin film material,the fibre material increased the response speed of the sensors.