Liquid flow electrification and zeta-potential in hydrocarbons

Abstract

It has been shown thatinjections of ions by electrodes into hydrocarbons is mainly controlled by the image-force (Schottky) barrier. Besides, ion injection appears to be electrochemical in nature. According to electrochemistry, injection and flow electrification are related phenomena. In the first case, ions generated within the double layer are carried away by a field, in the second, by mere diffusion. As a sequence, the concentration of these ions near the interface is expected to be larger than that in the bulk of the liquid by several orders of magnitude, giving a zeta-potential of 100 to 200 millivolts. Experiment, however, often gives values that are considerably lower, sometimes by an order of magnitude (10 to 20 millivolts). In this paper, the effect of the Schottky barrier on electrification is examined. It is found that for small ions the zeta-potential can be lowered by an order of magnitude, in agreement with experiment. The ion distribution within the range of the image force does not contribute appreciably to the electrification current, since it is restricted to an extremely thin layer (10 −6 cm). Thus, injection and electrification can be consistently related to the same electrochemical model, taking into account the important part played by the image force in non polar liquids.