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The motion of space charge initially located at the free surface of an insulator is studied as a function of time. Analytic results are given for the following cases: (a) mobility proportional to a power of the field; (b) mobility proportional to a power of the free-carrier concentration; and (c) fast deep trapping which goes to completion. After one transit time, the surface voltage becomes a unique function of time, independent of its initial value. The available experimental data for polyethylene do not fit these simple models, and the discrepancies are discussed. It is also shown that the observation of thermally stimulated currents in thin-film electrets implies that they are electrically inhomogeneous.

The electrical conductivity of polymers must be understood in order to improve their performance as electrical insulators. At the present time, there is a need to produce materials with lower conductivity than is currently available without compromising the desirable mechanical properties in order to satisfy the continuing demand for high-quality communications cables and optical fibers and for low-loss conventional power apparatus and cables. A further requirement will be for better standoffs for superconducting power cables. At the same time, there are other applications in which a somewhat larger conductivity would be desirable. These include the problems of static electrification of clothing, carpeting, phonograph records, and satellite antenna bushings, for which the existing palliative measures are not entirely satisfactory. Additional uses which need precise knowledge of the conduction mechanism include electrostatic recording (xerography), electrets (electroacoustic, pyroelectric, and biomedical applications), capacitor dielectrics, and films formed by glow discharge polymerization (switching devices and passivation of semiconductors). A more general background is helpful for interpreting the images obtained by scanning electron microscopy in the conduction mode.

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