Microviscosity of an ion-conducting polymer probed by fluorescence depolarization and dielectric spectroscopy

The local segmental motions of polypropylene oxide melt with variable amounts of added LiClO₄ salt (0.3-2.2 mol% per repeat unit) were studied using dielectric relaxation spectroscopy and single photon counting methods after two-photon excitation of an unattached fluorescent dye, rhodamine123, embedded at low concentration within the polymer. The lithium ions serve as junctions between polymer chains and increase the bulk viscosity. The measured microviscosity contains information on the local environment of ClO₄⁻ ions.