Considerations in charge transfer by transient contact of small particles

The author addresses the transfer of charge during collisions between small particles, idealized as spheres, in terms of classical electrostatics. The topics considered include the distribution of charge between spheres of different radii left in contact for a long time and the rate of transfer through finite resistances during transient contact. The model has implications for a variety of phenomena from the charging of hail stones to triboelectric effects in dry powders such as sugar, flour, and xerographic toner particles. An attempt is made to develop a simple two-body model for charge transfer between colliding spheres which will provide a framework to answer questions about equilibrium charging and rate of exchange if only classical electrostatics were applicable. This sets the stage for inferences about many-body processes and the modifications that quantum mechanics might impose