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Reversible electrowetting transitions on superhydrophobic surfaces
Physical Chemistry Chemical Physics ( IF 3.3 ) Pub Date : 2021-11-05 , DOI: 10.1039/d1cp04220c
D Vanzo 1 , A Luzar 1 , D Bratko 1
Affiliation  

An electric field applied across the interface has been shown to enable transitions from the Cassie to the Wenzel state on superhydrophobic surfaces with miniature corrugations. Molecular dynamics (MD) simulations manifest the possibility of reversible cycling between the two states when narrow surface wells support spontaneous expulsion of water in the absence of the field. With approximately 1 nm sized wells between the surface asperities, the response times to changes in the electric field are of O(0.1) ns, allowing up to GHz frequency of the cycle. Because of the orientation preferences of interfacial water in contact with the solid, the phenomenon depends on the polarity of the field normal to the interface. The threshold field strength for the Cassie-to-Wenzel transition is significantly lower for the field pointing from the aqueous phase to the surface; however, once in the Wenzel state, the opposite field direction secures tighter filling of the wells. Considerable hysteresis revealed by the delayed water retraction at decreasing field strength indicates the presence of moderate kinetic barriers to expulsion. Known to scale approximately with the square of the length scale of the corrugations, these barriers preclude the use of increased corrugation sizes while the reduction of the well diameter necessitates stronger electric fields. Field-controlled Cassie-to-Wenzel transitions are therefore optimized by using superhydrophobic surfaces with nanosized corrugations. Abrupt changes indicate a high degree of cooperativity reflecting the correlations between the wetting states of interconnected wells on the textured surface.

中文翻译:

超疏水表面上的可逆电润湿转变

已显示在界面上施加的电场能够在具有微型波纹的超疏水表面上从 Cassie 状态转变为 Wenzel 状态。分子动力学 (MD) 模拟表明,当狭窄的地表井支持在没有磁场的情况下自发排出水时,两种状态之间存在可逆循环的可能性。在表面凹凸不平之间有大约 1 nm 大小的井,对电场变化的响应时间为 O(0.1) ns,允许高达 GHz 的循环频率。由于与固体接触的界面水的取向偏好,该现象取决于垂直于界面的场的极性。对于从水相指向表面的场,Cassie-to-Wenzel 转变的阈值场强明显较低;然而,一旦处于 Wenzel 状态,相反的磁场方向可以确保井的更紧密填充。在降低场强时延迟的水回缩揭示的相当大的滞后表明存在适度的排出动力障碍。已知这些屏障大约与波纹长度比例的平方成比例,因此无法使用增加的波纹尺寸,而减小阱直径则需要更强的电场。因此,通过使用具有纳米级波纹的超疏水表面来优化场控制的 Cassie-to-Wenzel 转变。
更新日期:2021-11-30
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