Polarization-Depolarization Current (PDC) Measurements for Volume and Surface Resistivity Analysis of Polymeric Materials

Resistivity investigations of polymers by polarization-depolarization current (PDC) measurements are often limited due to the high resistivity of these materials. In the present work, this technique, which is established especially for insulating liquids and pressboard, is applied to a broad range of polymeric samples for both volume and surface resistivity analysis. For this purpose, an appropriate PDC setup is presented and crucial prerequisites for accurate low-current measurements in the (sub-)pA range are discussed. The results demonstrate that a steady-state volume resistivity measurement result is reached much faster than with classic polarization current measurements. Even for surface resistivity measurements, benefits are achieved by PDCs as they are shown to reveal the time-characteristics of parasitic volume currents and/or surface charge accumulation. Volume resistivity determination by PDC measurements indicate the presence of electrode-controlled Schottky conduction for the investigated samples. Large resistivity variations (almost two orders of magnitude) and non-uniform electric field dependences are found between different types of electrode-sample contacts. In order to evaluate the influence of different electrode-sample contacts, a method based on broadband dielectric spectroscopy (BDS) is proposed and applied. It also allows the estimation of the average air gap between sample and applied electrodes. Furthermore, it is found that dielectric microlayers of adhesive tape electrodes strongly influence the measured permittivity and resistivity values especially for thin samples by introduction of additional polarization processes.