Surfactant and dilatational viscosity effects on the deformation of liquid droplets in an electric field
Surfactant and dilatational viscosity effects on the deformation of liquid droplets in an electric field
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表面活性剂和膨胀粘度对电场中液滴变形的影响
DOI：
10.1016/j.jcis.2021.07.105
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发表时间：
2022
影响因子：
9.9
通讯作者：
Maldarelli, Charles
中科院分区：
文献类型：
--
作者：
Han, Yu;Koplik, Joel;Maldarelli, Charles
假设悬浮在绝缘连续相（例如油中的含水电解质）中的导电液滴在施加的电场的作用下变形为非球形平衡形状，甚至可以在强场下破裂。许多技术利用电变形来操纵流体分散体，液滴界面上存在表面活性剂，形成稳定的单分子层。虽然表面活性剂降低了界面张力，有利于电变形，但单层弹性可抵抗变形。高分子量表面活性剂具有较大的膨胀粘度，可能会延迟变形动力学。数值边界积分方法模拟均匀场中电介质中完美导电液滴的动态界面变形。该界面包含不溶性单分子层，该单分子层是具有恒定膨胀粘度且遵循朗缪尔状态方程的牛顿流体。研究了一系列初始表面活性剂表面浓度，弹性与浓度成正比。研究发现 平衡滴变形不受表面粘度的影响，在高表面浓度下受到弹性的强烈抵抗，并且破裂所需的场强随着弹性的增加而增加。膨胀粘度与表面粘度（除以液滴半径）与体积粘度的比率 κ* 成正比，并且可以延长变形时间。延长的时间通过与 κ* 成比例的时间重新缩放来描述。
Hypothesis A conducting droplet suspended in an insulating continuous phase, eg an aqueous electrolyte in an oil, is deformed by an applied electric field to nonspherical equilibrium shapes, and can even break-up under strong fields. Many technologies use electro-deformation to manipulate fluid dispersions, with surfactants present on the droplet interfaces forming stabilizing monolayers. While surfactants lower the interface tension which facilitates electro-deformation, the monolayer elasticity resists deformation. High molecular weight surfactants, with large dilatational viscosities, can potentially retard the deformation dynamics. Numerics A boundary integral method simulates the dynamic interfacial deformation of a perfectly conducting droplet in a dielectric in a uniform field. The interface contains an insoluble monolayer which is a Newtonian fluid with constant dilatational viscosity obeying a Langmuir state equation. A range of initial surfactant surface concentrations are studied, with elasticity proportional to concentration. Findings Equilibrium drop deformations, unaffected by surface viscosity, are strongly resisted by elasticity at high surface concentrations, and field strengths necessary for break-up increase with elasticity. Dilatational viscosity scales with the ratio, κ∗, the surface viscosity (divided by the droplet radius) to the bulk viscosity, and can extend the deformation time. Extended times are described by a time rescaling proportional to κ∗.