Sengupta Rajarshi, Khair Aditya S, Walker Lynn M
Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
J Colloid Interface Sci. 2020 May 1;567:18-27. doi: 10.1016/j.jcis.2020.01.081. Epub 2020 Jan 25.
Electric fields enhance surfactant transport to oil-water interfaces when the surfactant forms charged aggregates in the oil phase. Hence, transport under electric fields could be used to detect charged surfactant aggregates in nonpolar media.
Two surfactants with different architecture were dispersed in Isopar-M. The transport of surfactants to an oil-water interface under a constant electric field was quantified using a custom-built electrified microtensiometer platform. Electrical conductivity of the oil with surfactant concentration was also measured to determine the presence of charge carriers.
The charging mechanism of the oil phase, and field-enhanced transport was different for the two surfactants. At low concentrations where the electrical conductivity of the surfactants is indistinguishable, dynamic interfacial tension measurements under electric fields can ascertain the presence of charge carriers in Isopar-M. The transport of ionic surfactants in the aqueous phase was unaffected by the field, confirming that the field-enhanced transport of oil-phase surfactants is due to electrophoresis of charge carriers. Moreover, the equilibrium interfacial tension was not found to change under an electric field, suggesting the adsorption isotherm is independent of the field strength. We demonstrate that dynamic interfacial tension measurements under electric fields is a sensitive technique to detect charge carriers in nonpolar fluids.
当表面活性剂在油相中形成带电聚集体时，电场会增强表面活性剂向油水界面的传输。因此，电场作用下的传输可用于检测非极性介质中的带电表面活性剂聚集体。
将两种具有不同结构的表面活性剂分散在异壬烷中。使用定制的带电微张力计平台对恒定电场下表面活性剂向油水界面的传输进行定量分析。还测量了含有表面活性剂的油的电导率，以确定电荷载流子的存在。
两种表面活性剂的油相充电机制和场增强传输有所不同。在表面活性剂电导率无法区分的低浓度下，电场下的动态界面张力测量可以确定异壬烷中电荷载流子的存在。离子型表面活性剂在水相中的传输不受电场影响，这证实了油相表面活性剂的场增强传输是由于电荷载流子的电泳作用。此外，未发现平衡界面张力在电场下发生变化，这表明吸附等温线与场强无关。我们证明，电场下的动态界面张力测量是检测非极性流体中电荷载流子的一种灵敏技术。
