Surface component of vacuum absorption and resorption currents in polymers. II. Surface charge accumulation

For pt.I see ibid., vol.13, p.625 (1980). Approximate relative magnitudes of the bulk and surface components of absorption/resorption currents in six organic polymers have been determined in vacuum, using a twin electrometer technique. The surface components approach 100% of the total current in polytetrafluoroethylene and polyethylene, 60% in polystyrene and a co-polymer of hexafluoropropylene and tetrafluoroethylene, but are very small in polyvinylchloride and polyethyleneterephthalate. The accumulation of charge on the polymer surface adjacent to the electrode edge has been monitored directly, using a series of shielded probes of varying sizes. Although the strength of the electric field applied for periods up to 12 h exceeded 10 6 V m -1 , the accumulated charge on the surface of a polyethylene sample did not extend more than 18 mu m beyond the edge of an aluminium electrode in the form of a thin strip. It seems likely that, when the samples are short-circuited, the resorption current is due to the return of the accumulated charge to the electrode, under its self-field. The observed t -1 time-dependence of the absorption current is incompatible with charge transport on the surface via a pure diffusion process.