Transient Liquid Motion Induced by Charge Injection from Plane Polymer Sheets

An effort is made to acquire a better understanding of the electrical properties of polymer/liquid interfaces as encountered in various electrotechnical applications such as power capacitors, solid spacers, etc. The diffuse part of the electric double layer built up at the solid/liquid interfaces is shown to act as a reservoir of carriers, and when the interface is perpendicular to the field, electrohydrodynamic (EHD) motion occurs. In view of studying these transient effects, a step change of voltage is applied to a solid/liquid/solid plane capacitor which produces the blocking of one charged layer and the displacement of the other. At low fields, the transient currents I(t) are very similar to space charge limited currents (SCLC's) (taking into account the eventual induced motion). At higher fields, the shape of the I(t) curve differs from the SCLC curve and takes the form expected for a thin charged layer transfer. Above a critical voltage, EHD instability sets in. We present the main characteristics of this instability and show analogies and differences with EHD phenomena during transient SCLC unipolar injections. These results will be useful to the study of electrokinetic phenomena and in electrical engineering in the field of breakdown along spacers.