Piezo- and pyro-electricity in polymer electrets

In 1960 Gubkin
¹
published an electrostatic theory of piezoelectricity which did not involve the microscopic structure of the electret. This approach would seem to be a good description of the phenomenon of piezoelectricity in polymer materials, many of which are partially or completely amorphous. We applied Gubkin's model to a specific set of experimental conditions, which resulted in some simplifications. These conditions are: 1. We measure changes in surface charge at nearly zero potential. 2. We use thin evaporated metal electrodes so that the electrodes change area in accord with changes in specimen area, A. 3. We consider only amorphous specimens which we assume to be elastically isotropic. 4. We assume the free charges to be frozen in the solid and to move in proportion to macroscopic strains, and the polarization charges to be rigid molecular dipoles whose positions move in proportion to macroscopic strains but whose effective total moment remains constant as long as the strains are isotropic.