Effective polarization fatigue in cellular polypropylene ferroelectrets

Abstract

Polymer foams with internally charged voids exhibit high piezoelectric activity combined with a high mechanical flexibility and compliance. This new class of materials (so-called ferroelectrets) has attracted considerable attention from science and industry. In order to render polymer foams electroactive, the inside voids must be charged by means of dielectric barrier discharges (DBDs) under high external electric fields. In DBDs, at least one side of the discharge gap is insulated from the electrodes by a dielectric layer. However, DBDs produce a variety of species including energetic and reactive monoatomic and molecular diatomic charged particles, electrons, and neutral species. Therefore the inner surfaces of the voids are exposed to a highly reactive plasma during the DBD poling. The repeated DBDs in air result in significant fatigue of the effective polarization and hence the piezoelectricity of cellular polypropylene (PP) ferroelectrets due to plasma-surface interactions on the internal void surfaces. In this paper, the dependence of the fatigue rate on the amplitude and the number of cycles of the driving voltage is studied, and the recovery behavior of the fatigued samples is explored.