Polymer electrolytes confined in nanopores: using water as a means to explore the interfacial impedance at the nanoscale

Nanoscale impedance measurements were obtained for polyethylene oxide (PEO) polymer electrolytes confined in porous polycarbonate membranes. Data were acquired using an atomic force microscope coupled with a.c. impedance spectroscopy, which allowed nanometer-size areas of the surface to be examined. It was found that impedance varied little for measurements inside, at the edge or outside an individual pore. Impedance characteristics were also monitored under varying conditions of temperature and relative humidity, to explore the effects with exposure to water vapor. The combined AFM-impedance technique made it possible to monitor events such as water adsorption and absorption at the nanoscale. Impedance data showed little change with water adsorption on the surface. Upon water absorption into the film, impedance values immediately decreased. Absorption also resulted in the appearance of a shoulder on the low-frequency portion of the impedance curve. It is suggested that this feature indicates water absorption at the polyethylene oxide-polycarbonate interface. (C) 2004 Published by Elsevier B.V.