(531a) Dynamic Interfacial Tension Measurement Under Electric Fields Allow Detection of Charge Carriers in Nonpolar Liquids

Electric fields enhance surfactant transport to oil-water interfaces when the surfactant forms charged aggregates in the oil phase. The tendency of surfactant aggregates to acquire charge depends on surfactant architecture, and the solvent in which the surfactant is dispersed. In this study, we disperse two surfactants with different architecture in Isopar-M, and using a custom-built electrified microtensiometer platform, quantify the transport of surfactants to the oil-water interface under a constant electric field. Electrical conductivity of the oil with increasing surfactant concentration was measured to determine the presence of charge carriers. The charging mechanism of the oil phase, and the transport under an electric field was different for the two surfactants. At low concentrations where the electrical conductivity of the two surfactants are indistinguishable, dynamic interfacial tension measurements under electric fields can ascertain the presence of charge carriers in the oil phase. Experiments on the transport of ionic surfactants in the aqueous phase did not show an electric field-dependent effect, confirming that the field-enhanced transport of oil-phase surfactants is due to electrophotresis of charge carriers. Moreover, the equilibrium interfacial tension was not found to change under an electric field, suggesting the adsorption isotherm is not a function of the field strength. We demonstrate that dynamic interfacial tension measurements under electric fields is a sensitive technique to detect the presence of charge carriers in a nonpolar fluid.