Tribocharging and the Triboelectric Series

Abstract Tribocharging is a process in which materials contact one another, rub, and then separate, each with a resulting charge distribution that is generally uniform on a macroscopic level but may involve mosaics of both positive and negative charges on each material on the microscopic level. This process is familiar and applied extensively in processes such as electrophotography, energy harvesting, and self‐powered sensors, but it is not completely understood. The triboelectric series is a qualitative or semiquantitative ordering of materials according to their tendency to develop a positive or negative net charge when tribocharged against other materials. It is remarkable that, despite differences in surface preparation, modes of contact among materials, and laboratory conditions, triboelectric series generated by different groups remain largely consistent with each other. This article examines a variety of triboelectric series, discrepancies among them, and the possible competing mechanisms behind tribocharging and contact electrification in general. These mechanisms appear to include electron transfer, ion transfer, H + and OH − partitioning, bond dissociation, mechanoradical formation, chemical changes, and material transfer. Combinations of these mechanisms may occur simultaneously but at different rates, which may help to explain some of the inconsistencies among different triboelectric series.