Electric properties of polyelectrolyte films in moist solvents

Films made of interpenetrated networks of a polymer and a polyelectrolyte, containing quaternary ammonium groups and bromide as counter-ion, and deposited onto interdigitated gold electrodes, were investigated by frequency response analysis as sensitive materials for the detection of water traces in organic solvents. Remarkable variations of both the resistance and the capacitance of the polyelectrolyte were observed by changing the water concentration in the solvents. Furthermore, materials with different ion concentration showed a similar behaviour, also for different solvents. The strongest conductance variation occurred in a very narrow range of water concentration and that range shifted toward higher values as the dielectric constant of the solvent increased. By increasing the water content, the film resistance and the ratio between the capacitance at the electrodes and the capacitance of the film reached limit values, non depending on the limit concentration of water in the solvent. The analysis of the impedance spectra suggested a model for the partition of water among the solvent, the polymer and a phase located at their interface.