Electron-Induced Conduction in Plastics. II. Bulk Excitation in Polystyrene and Other Insulating Polymers

The electrical conduction in a number of commercial plastics has been studied under pulsed bombardment by fully penetrating electrons. Detailed results are given mainly for polystyrene. The kinetics obeyed by the ``prompt'' component of the induced current are predominantly first order, those of the ``long-lived'' current, second order. The results generally support the assumptions made in Paper I, and in particular confirm the interpretation of the decay time of the long-lived current as a bimolecular recombination lifetime. A simple model for radiation-induced conduction in polymers, based on topological considerations, is developed. The prompt component is identified with intramolecular carrier drift. The mobility in this process has a lower limit of 10−2 cm2/Vsec. The long-lived current is associated with intermolecular jumps. It is suggested that, while the effective mobility of the long-lived component (as determined in Paper I) in kinked-chain polymers is controlled by the intermolecular jump probability, that in polyethylene is subject to an additional limitation, viz. strong localization of carriers in the U bends of the molecules.