Electric charging of inverse micelles in a nonpolar liquid with surfactant

The origin of charges in nonpolar liquids with surfactant is not completely understood. This study does not only look at bulk mechanisms as the origin of charged inverse micelles, but includes processes at the liquid/electrode interfaces. We apply a voltage over a layer of nonpolar liquid with surfactant and measure the current. Information about the generation of new charges is obtained from the remaining current after the initially present charges have reached equilibrium. We find that, for low voltages, the residual current is proportional with the electric field near the electrodes. This can not be explained by bulk generation alone. We interpret these results by assuming that inverse micelles exchange charge with an adsorbed layer of surfactant molecules at the electrodes. The findings of this study are relevant for technologies such as microfluidics and electrophoretic ink, where injection of charge from the electrodes contributes to power consumption and hydrodynamic instabilities.

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► Current measurements in response to a voltage step provide information about the origin, nature and properties of charges in nonpolar liquids.
► A model for the generation of charged inverse micelles needs to include both bulk and surface interactions.
► Inverse micelles exchange charge with an adsorbed layer of surfactant molecules at the electrodes.