CONTACT ELECTRIFICATION OF INSULATORS AND ITS RELEVANCE TO ELECTRETS

Surface charge densities on electrets are frequently measured by means of electrodes which can be lifted from the insulator surface; however, electrification of the surface can occur as a result of this contact between electrode and insulator, and this can be a source of difficulty in interpreting the results. In these experiments, measurements have been made on the contact electrification of paraffin, polystyrene, and polyethylene, among other materials, using mercury as the electrode. In these cases it is found that the contact charge exchange decreases with decreasing contamination of the insulator. Under controlled conditions, equilibrium surface charge densities as low as 0.003 nC/cm2 have been observed for paraffin. When the contact event produces both high electric fields and also high local surface potentials, the surface charge causes electrical breakdown during the separation of insulator and electrode. We find that it is useful to “develop” the resulting electrostatic charge distribution by xerographic means. The resultant charge distribution frequently shows the gross patchy structure of Lichtenberg figures previously reported for high voltage discharges to insulators in air. © 1968, The Electrochemical Society, Inc. All rights reserved.