Research On Humidity Sensing Properties Of Vanadic Acid Base,poly Aniline And Their Composites

Poly-vanadium-titanium acid xerogel thin films have been prepared by sol-gel methodusing V2O5, tetrabutyl titanate and H2O2as the precursors. The obtained xerogels wereinvestigated by FTIR and XRD methods. The content of titanium and the thickness of thinfilms on the humidity sensing properties of the prepared thin films were discussed. Thehumidity sensitive properties, the response-recovery behavior and long-term stability of thethin films were studied. But its long-term stability is not good, needing to improve.The proton acid doped polyaniline have been prepared by chemical oxidativepolymerization, The humidity sensing properties'results show that The resistance changes anorder of magnitude at all the relative humidity. Its humidity sensing properties and long-termstability need to be futher improved.In order to increase humidity sensing properties of polyaniline, using blending andcompound methods prepared polyaniline/poly-vanadium-titanium acid composites andstuding on its humidity sensing properties. Results show that after the compound, thehumidity sensor's humidity-sensitive properties are better than polyaniline.The doping of polyaniline is another way to increase humidity sensing properties ofpolyaniline.The vanadic acid and vanadium-titanium acid doped polyaniline have beenprepared by precipitation polymerization using ethanol as the emulsion. The properties werecharacterized by FTIR, UV-vis and XRD methods. The reaction temperatures, antioxidants, n(H2VxTiyO30-z·nH2O)/n(An), immersion times and impregnating time on humidity sensingproperties were discussed and the optimum reaction conditions were determined. Theresults indicate that the humidity sensing properties'of polyaniline doped withvanadium-titanium acid are better than vanadic acid doped polyaniline humidity sensor.Thehumidity sensor of vanadium-titanium acid doped polyaniline's resistance and capacitancechanged with the relative humidity and frequency. When the frequency is1kHz, the log-linearrelationship of resistance with the relative humidity is good. Humidity sensors' resistancechange3orders magnitude and the humidity sensitivity is good in the range of11%~97%.The hysteresis is5%RH and response,recovery are respectively5s and19s. The humiditysensor has a good humidity sensing properties, compared withsingle and composite humiditysensors, its humidity sensing properties have a significantly improving and enhancing.