Effects of humidity and various gases on the electrical conductivity of polyethylene glycol

Abstract

Characterization of the electrical properties of covalently linked pure, hydrogenated and hydrophobically modified poly{ethylene glycol} (PEG) thin films under a changing relative humidity is examined by dc measurements. Perfluoroalkylethylalcohol is used as the hydrophobic additive. At low humidity levels, electronic conduction takes place while the absorbed water contributes to this mechanism and increases the current. At around 70% relative humidity, as a result of the water clusters formed, the polymer melts from the semicrystalline form and the current shows a steeper increase. The water vapor condenses and conduction takes an ionic nature. For the pure PEG samples, after 75%, the conductivity shows irregularities with respect to increase in the relative humidity. The irregularities subside in the hydrogenated as well as the hydrophobically modified PEG samples, while in the latter the steep increase in conductivity shifts to higher values of relative humidity with increase of perfluoroalkylethylalcohol concentration in the film. There is a hysterisis between the absorption and desorption of water as the film cannot reach its semicrystalline form in the time interval of desorption. The polymer film could get its pre-absorption form after annealing. The response of PEG thin films to the exposure to acetone and methanol vapor at changing pressures are observed by dc measurements under vacuum. The conductivity of the polymer increases with the increasing pressure of vapor while this increase reaches a significant value at 1100 Pa. Acetone causes an augmentation in current 10 times greater than methanol due to the difference between their dielectric constants.