Mechanism for Asymmetric Nanoscale Electrowetting of an Ionic Liquid on Graphene.
Mechanism for Asymmetric Nanoscale Electrowetting of an Ionic Liquid on Graphene.
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DOI：
10.1021/acs.langmuir.5b04161
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发表时间：
2016-01
期刊：
影响因子：
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通讯作者：
Fereshte Taherian;F. Leroy;L. Heim;E. Bonaccurso;N. V. D. van der Vegt
中科院分区：
文献类型：
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作者：
Fereshte Taherian;F. Leroy;L. Heim;E. Bonaccurso;N. V. D. van der Vegt
采用分子动力学模拟方法研究了1-丁基-3-甲基咪唑四氟硼酸盐（[bmim][BF 4]）在两个带相反电荷的石墨烯层之间的电润湿行为。通过在表面上引入电荷，抗衡离子被吸引到表面，共离子被排斥，导致固-液界面自由能降低，从而接触角降低。最近，我们已经表明，在充电的表面接触角的变化是不对称的表面极性和相反的固-液界面自由能的变化。在这项工作中，固-液界面自由能的不对称性被证明是源于在界面处的离子的结构组织的差异，与正极化表面诱导更有利的离子的静电排列。然而，在三相接触线附近的液体结构的分析表明，离子尺寸的不对称性，以及在相反的极化表面上的阳离子的取向排序的差异，而不是导致增强的负极化表面上的扩展，导致相应的接触角不对称性。
The electrowetting behavior of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) confined between two oppositely charged graphene layers is investigated using molecular dynamics simulations. By introducing charges on the surface, counterions are attracted to the surface and co-ions are repelled from it, leading to the reduction of the solid-liquid interfacial free energy and consequently the contact angle. Recently, we have shown that changes in the contact angle upon charging the surface are asymmetric with respect to surface polarity and opposite to the changes in the solid-liquid interfacial free energy. In this work, the asymmetry of the solid-liquid interfacial free energy is shown to originate from differences in structural organization of the ions at the interface, with positively polarized surfaces inducing a more favorable electrostatic arrangement of the ions. Analysis of the liquid structure in the vicinity of the three phase contact line, however, shows that the ion size asymmetry, together with differences in orientational ordering of the cations on oppositely polarized surfaces, instead leads to enhanced spreading on the negatively polarized surfaces, resulting in a corresponding contact angle asymmetry.