Gas And Humidity Sensitive Properties Of Water Dispersed Nano-sized Polyaniline And Its Composite

The humidity sensitive materials based on water dispersed nanosized polyaniline (PANi-PSSA) with polystyrene sulfonic acid (PSSA) as a template, and the gas sensitive materials based on water dispersed polyaniline nanoparticle codoped with PSSA and p-toluene sulfonic acid (TSA) were designed and prepared. The structure and morphologies of the sensitive materials were characterized by UV-Vis,FT-IR,SEM,AFM and cyclic voltammograms, etc. Resistive-type humidity sensor and gas sensor were conveniently constructed by dip-coating, and their humidity sensitive properties and gas sensitive properties toward triethylamine (TEA) vapor have been investigated at room temperature. The effects of the composition, structure and preparation techniques of the sensors on their humidity and gas sensing characteristics were discussed. The humidity and gas sensitive mechanisms were explored.The effects of the ratios of PSSA to aniline, the polymerization temperature, the concentration of dip-coating solution, the configuration of the electrode and forming composite with poly(vinyl alcohol) (PVA) on the humidity sensitive properties of PANi-PSSA were investigated. It was found that the humidity sensor exhibited good sensing linearity on a semi-logarithmic scale in the range of 15-97%RH, fast response (response time of 6 s and 10 s for adsorption desorption, respectively). The humidity sensitivity was improved with the increase in the ratio of PSSA to aniline. Moreover, the composite of PANi-PSSA with PVA showed a small hysteresis of 2%RH and good sensing linearity (R~2=0.999). The humidity sensing mechanism was explored by measuring their complex impedance and it was revealed that both the electronic and ion conductivity played a role in its conduction behavior.The effects of the concentration of oxidants, polymerization temperature, concentration and type of the dopants on the sensitive properties of the water dispersed polyaniline nanopaticles towards TEA vapor were investigated. It was found that the sensitivity of the sensor reached 3.5-126% in the range TEA vapor of 1-300 ppm, and response was fast. Moreover, the response is reversible towards TEA vapors of both high concentration (200 ppm) and low concentration (25 ppm). The i-v curve of the gas sensitive materials was measured under different atmosphere, which revealed an ohmic contact between the sensitive film and underlying electrode. The sensing mechanism of the polyaniline based gas sensor toward TEA vapor was also investigated.