The effect of humidity on the electrical behavior of a cationic conjugated polyelectrolyte based on poly(phenylene vinylene)

A cationic conjugated polymer based on poly(phenylene vinylene) was prepared by Glich dehydrohalogenation polymerization. The structure of the polymer was characterized by 1H NMR, Fourier transformed infrared spectroscopy, UV–visible spectroscopy, photoluminescent spectroscopy and thermogravimetric analysis. The polymer was deposited on interdigitated gold electrodes by dip-coating, and its electrical responses to humidity were investigated at room temperature over the range of 22–97%RH. It was found that the polymer exhibited a high sensitivity, as characterized by impedance change almost linearly on a semi-logarithmic scale from 107 to 104 Ω when humidity decreased from 22 to 97%RH. In addition, fast response (t90% ∼7 s and ∼5 s for absorption and desorption, respectively) and moderate hysteresis (∼6%RH) were observed. It is proposed that both the pendant ionic group of the cationic conjugated polymer and the π-conjugated backbone affected its humidity sensing behaviors.