Plastic Electrets

Abstract

A brief discussion of proposed explanations for the electret effect is presented. Plexiglas, Lucite, and Nylon electrets were prepared under fields ranging from 19 to 36 kv/cm and observed for as long as 2000 hours. The surface charge densities were measured by electrostatic induction using a commercial electronic electrometer and a shunt capacitance to reduce the readings to a maximum of 20 volts. The initial state was a heterocharge or a homocharge depending on the strength of the forming field. The steady state was a homocharge in every case. Charge densities as high as 5.5×10⁻⁹ coulomb/cm² (16.5 esu) were observed. A Plexiglas disk was charged at room temperature under a strong field and its subsequent decaying homocharge recorded. The experimental results support the ideas of Mikola and Gross, i.e., the existence of two decaying polarizations of opposite sense due to ionic migration, one occurring within the dielectric, the other, across the electrode‐dielectric interface.