Octagon to Square Wetting Area Transition of Water–Ethanol Droplets on a Micropyramid Substrate by Increasing Ethanol Concentration

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• 作者：Huicheng FengKaren Siew-Ling Chong ; Kian-Soo Ong ; Fei Duan
• 刊名：Langmuir
• 出版年：2017
• 出版时间：February 7, 2017
• 年：2017
• 卷：33
• 期：5
• 页码：1147-1154
• 全文大小：658K
• ISSN：1520-5827

文摘

The wettability and evaporation of water–ethanol binary droplets on the substrate with micropyramid cavities are studied by controlling the initial ethanol concentrations. The droplets form octagonal initial wetting areas on the substrate. As the ethanol concentration increases, the side ratio of the initial wetting octagon increases from 1.5 at 0% ethanol concentration to 3.5 at 30% ethanol concentration. The increasing side ratio indicates that the wetting area transforms from an octagon to a square if we consider the octagon to be a square with its four corners cut. The droplets experience a pinning–depinning transition during evaporation. The pure water sessile droplet evaporation demonstrates three stages from the constant contact line (CCL) stage, and then the constant contact angle (CCA) stage, to the mixed stage. An additional mixed stage is found between the CCL and CCA stages in the evaporation of water–ethanol binary droplets due to the anisotropic depinning along the two different axes of symmetry of the octagonal wetting area. Droplet depinning occurs earlier on the patterned surface as the ethanol concentration increases.