Water-soluble polyaniline and its composite with poly(vinyl alcohol) for humidity sensing

Water-soluble polyaniline (PANi) was prepared by a “green” method with poly (stryrenesulfonic acid) (PSSA) as a template, and characterized by UV–vis spectroscopy, FT-IR spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM). It was found that the films of PANi and its composite with poly(vinyl alcohol) (PVA) were composed of nanoparticles. The humidity sensitive properties of the both PANi and its composite with PVA were investigated at room temperature. The water-soluble PANi exhibited high sensitivity (impedance change over three orders of magnitude in the range of 15–97%RH) and good sensing linearity on a semi-logarithmic scale, but a relatively large hysteresis of ∼8%RH. In contrast, the composite of PANi and PVA showed a very small hysteresis of ∼2%RH. Moreover, the response was fast and highly reversible. The humidity sensing mechanism of the composite of PANi with PVA was explored by measuring its complex impedance spectra under different humidities.