The humidity dependence of the electrical conductivity of a soluble polyaniline-poly(vinyl alcohol) composite film

A humidity-sensitive composite film has been synthesized that consists of soluble polyaniline (PAn) and poly(vinyl alcohol) (PVA). PAn gave a percolation threshold where the electrical conductivity rose sharply at a volume fraction of 0.1%. This value is very small compared with that (about 5 vol%) reported in general for composite films consisting of conducting and non-conducting polymers, indicating that the two polymers used in this study were mixing completely. The conductivity of the PAn-PVA composite was proportional to the relative humidity, and the linearity was valid from 3 x 10(-5) to 1.5 x 10(-1) S cm(-1). The response time of the composite for the humidity change was 45 s and 9 min for moistening and desiccating steps, respectively. The conductivity of the composite film varied depending on the doping level of PAn, which was affected by the concentration of water molecules surrounding the conducting polymer. At high humidity, the PAn was in the form of an emeraldine salt, and transformed into a non-conducting base with decreasing environmental humidity.