Polarization effects in PVB, Tedlar, and in a PVB/Tedlar composite as a function of humidity

Polarization effects in polyvinyl butyral (PVB), Tedlar (T) and in a PVB/T laminated composite have been investigated as a function of humidity by monitoring the time dependence of the current response to a step voltage forcing function. The current response in PVB, particularly at elevated humidities, exhibits an apparent two stage, power law, time dependence which suggests that the current response at all humidity levels could be modeled as the sum of two simultaneously occuring absorption current components Iw and Ip each characterized by a power law time dependence: The Iw absorption current component with its associated Iwo and αw kinetic parameters is believed to be governed by the polarization of the PVB dielectric due to the relatively rapid alignment of water molecules in any absorbed water that exists as a second phase in the free volume space of the PVB. The kinetically slower Ip absorption current component, characterized by the Ip0 and αp parameters, is suggested to result from the more gradual polarization of the PVB dielectric due to polar molecules in the polymer primary phase network. The current response characteristics in Tedlar and in PVB/T differ significantly from that observed in PVB, and could not be easily characterized by the water and polymer absorption current component model used to analyze the PVB data.