Surfactants (amphiphilic surface active agents) are often used to control the dynamics of viscous drops and bubbles in microfluidics applications. Surfactant sorption kinetics has been shown to play a critical role in the deformation of drops in extensional and shear flows, yet to the best of our knowledge these kinetics effects on a viscous drop in an electric field have not been accounted for. In this paper we numerically investigate the effects of sorption kinetics on a surfactant-covered viscous drop in an electric field. Over a range of electric conductivity and permittivity ratios between the interior and exterior fluids, we focus on the dependence of deformation and flow on the transfer parameter $J$, and Biot number Bi that characterize the extent of surfactant exchange between the drop surface and the bulk. Our findings suggest solubility affects the electrohydrodynamics of a viscous drop in distinct ways as we identify parameter regions where (1) surfactant solubility alters both the drop deformation and circulation of fluid around a drop and (2) surfactant solubility affects mainly the flow and not the deformation.

中文翻译：

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表面活性剂溶解度对直流电场中粘性液滴流体动力学的影响

表面活性剂（两亲表面活性剂）通常用于控制微流体应用中粘性液滴和气泡的动力学。表面活性剂吸附动力学已被证明在拉伸和剪切流中液滴的变形中起着关键作用，但据我们所知，这些动力学对电场中的粘性液滴的影响尚未被考虑在内。在本文中，我们数值研究了吸附动力学对电场中表面活性剂覆盖的粘性液滴的影响。在内部和外部流体之间的电导率和介电常数比范围内，我们关注变形和流动对传递参数的依赖性$J$，以及表征液滴表面和本体之间表面活性剂交换程度的 Biot 数 Bi。我们的研究结果表明，溶解度以不同的方式影响粘性液滴的电流体动力学，因为我们确定了参数区域，其中 (1) 表面活性剂溶解度改变液滴变形和液滴周围流体的循环和 (2) 表面活性剂溶解度主要影响流动而不是形变。