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How and When the Cassie–Baxter Droplet Starts to Slide on Textured Surfaces
Langmuir ( IF 3.7 ) Pub Date : 2020-11-11 , DOI: 10.1021/acs.langmuir.0c02614 Donggyu Kim 1 , Seunghwa Ryu 1
Langmuir ( IF 3.7 ) Pub Date : 2020-11-11 , DOI: 10.1021/acs.langmuir.0c02614 Donggyu Kim 1 , Seunghwa Ryu 1
Affiliation
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A theoretical analysis of the sliding of a Cassie–Baxter droplet on a microstructured surface is conducted. The conventional theory based on the force balance has been frequently used to predict the sliding condition of the droplet; however, the sliding condition cannot be precisely determined because the theory requires the available ranges of the contact angles at the rear and front ends of the droplet. In this study, by calculating the droplet shape and examining the stability of a droplet at every possible pinning point, we propose a new theoretical model that can predict the sliding condition of a two-dimensional (2D) Cassie–Baxter droplet without any a priori measurement but using only the surface information. With the proposed theory, we answer two open questions in sliding research: (i) whether the sliding initiates with front end slip or rear end slip and (ii) whether the advancing and receding contact angles measured on the horizontal surface are comparable with the front and rear contact angles of the droplet at the onset of sliding. Additionally, a new droplet translation motion mechanism promoted by a cycle of condensation and evaporation is suggested, which can be further utilized for precise droplet transportation. Finally, the theoretical results are validated against the 2D line-tension-based front-tracking method (LTM), which can seamlessly capture the attachment and detachment between the droplet and the textured surface.
中文翻译：
Cassie–Baxter液滴如何以及何时开始在带纹理的表面上滑动
对Cassie-Baxter液滴在微结构表面上的滑动进行了理论分析。基于力平衡的传统理论经常被用来预测液滴的滑动状态。然而，由于该理论要求液滴的前端和前端的接触角的可用范围，因此不能精确地确定滑动条件。在这项研究中，通过计算液滴形状并检查液滴在每个可能的钉扎点处的稳定性，我们提出了一个新的理论模型，该模型可以预测二维（2D）Cassie–Baxter液滴的滑动条件而无需先验测量，但仅使用表面信息。利用提出的理论，我们在滑动研究中回答了两个未解决的问题：（i）滑动是从前端滑移还是从后端滑移开始，以及（ii）在水平面上测量的前进和后退接触角是否与液滴在滑动开始时的前后接触角相当。另外，提出了一种通过凝结和蒸发循环促进的新的液滴平移运动机制，该机制可以进一步用于精确的液滴运输。最后，针对基于2D线张力的前跟踪方法（LTM）验证了理论结果，该方法可以无缝捕获液滴与纹理表面之间的附着和分离。
更新日期：2020-11-25
中文翻译：
Cassie–Baxter液滴如何以及何时开始在带纹理的表面上滑动
对Cassie-Baxter液滴在微结构表面上的滑动进行了理论分析。基于力平衡的传统理论经常被用来预测液滴的滑动状态。然而，由于该理论要求液滴的前端和前端的接触角的可用范围，因此不能精确地确定滑动条件。在这项研究中，通过计算液滴形状并检查液滴在每个可能的钉扎点处的稳定性，我们提出了一个新的理论模型，该模型可以预测二维（2D）Cassie–Baxter液滴的滑动条件而无需先验测量，但仅使用表面信息。利用提出的理论，我们在滑动研究中回答了两个未解决的问题：（i）滑动是从前端滑移还是从后端滑移开始，以及（ii）在水平面上测量的前进和后退接触角是否与液滴在滑动开始时的前后接触角相当。另外，提出了一种通过凝结和蒸发循环促进的新的液滴平移运动机制，该机制可以进一步用于精确的液滴运输。最后，针对基于2D线张力的前跟踪方法（LTM）验证了理论结果，该方法可以无缝捕获液滴与纹理表面之间的附着和分离。
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