Charge and polarization dynamics in polymer films

Recently nondestructive methods have been developed which make it possible to investigate layered charge and dipolar distributions in dielectric materials within an order of 1 μm resolution. These direct methods which do not use mathematical deconvolution techniques are the LIPP-[1] and the PPS-method [2]. The PPS-method operating with an almost ideal acoustic step excitation results in getting an 1:1-image of the longitudinal piezoelectric distribution within a thin film as demonstrated for PVDF by Haardt [3J. The results are consistent with charge compensated polarization layers within incompletely poled films. In order to obtain more informations on the possible reasons for these distributions we investigated the time dependence of the step response signal during poling. The nature of the compensation charges appears to be ionic as consistent with the pressure dependence of conductance.