Humidity Sensors And Humidity Sensitive Properties Based On Polymer Nanocomposite

Four kinds of humidity sensitive materials, namely, composites of graphene and linear polyelectrolytes, graphene and silicon-containing polyelectrolytes, processable polypyrrole (PIL-PPy) and quarternized and crosslinked poly(4-vinylpridine)(QCP4VP), water-dispersible polyaniline and polyvinyl alcohol, were prepared and characterized by1HNMR, FT-IR, SEM, TEM, etc. Impedance-type and surface acoustic wave (SAW)-impedance type humidity sensors based on the composites were constructed with dip-coating method. Humidity sensing properties, especially humidity sensing characteristics at low humidity, of the sensors have been investigated and their sensing mechanism was explored.Poly(dimethyl diallyl ammonium chloride)(PDDA)/GN and sodium poly(styrene sulfonate)(PSSNa)/GN prepared by solution blending and in-situ reduction. PAPTS/GN was prepared via solution blending and heat-induced simultaneous cross-linking and reduction. Impedance-type humidity sensors based on the composites were fabricated by dip-coating. It was found that introduction of graphene lowered impedance of the composite sensors significantly even at very low humidity levels. As-prepared humidity sensors exhibited high sensitivity, fast response and good sensing linearity to humidity at0.2%-30%RH. Complex impedance analysis revealed that both resistance and capacitance components of the composites changed greatly due to the addition of graphene, which is responsible for the improved sensing characteristics of the composite sensors to low humidity.QCP4VP/PIL-PPy were facilely prepared by solution blending, and used to fabricate thin film impedance-type humidity sensors by dip-coating. The composite sensors displayed impedance change of four orders of magnitude over the range of10-97%RH, showing high sensitivity and good sensing linearity on a semi-logarithmic scale. Moreover, they were featured with very small hysteresis. Composite of polyaniline and polyvinyl alcohol was obtained by solution blending. SAW-impedance type humidity sensors based on the composite were constructed by dip-coating. Effect of concentration of polyaniline on sensing behavior of the sensors has been examined. The novel humidity sensors exhibited high sensitivity (2.2kHz%RH) at low humidity levels (0.4-20%RH), fast response and good stability.