Feng Huicheng, Chong Karen Siew-Ling, Ong Kian-Soo, Duan Fei
School of Mechanical and Aerospace Engineering, Nanyang Technological University , 50 Nanyang Avenue, Singapore 639798, Singapore.
Institute of Materials Research and Engineering , A*Star, 2 Fusionopolis Way, Innovis, Level 9, Singapore 138634, Singapore.
Langmuir. 2017 Feb 7;33(5):1147-1154. doi: 10.1021/acs.langmuir.6b04195. Epub 2017 Jan 26.
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.
通过控制初始乙醇浓度，研究了具有微金字塔形孔洞的基底上乙醇 - 水二元液滴的润湿性和蒸发情况。液滴在基底上形成八边形的初始润湿区域。随着乙醇浓度的增加，初始润湿八边形的边长比从乙醇浓度为0%时的1.5增加到乙醇浓度为30%时的3.5。边长比的增加表明，如果将八边形视为四个角被切掉的正方形，那么润湿区域从八边形转变为正方形。液滴在蒸发过程中经历钉扎 - 脱钉转变。纯水固着液滴蒸发呈现出三个阶段，从恒定接触线（CCL）阶段，然后是恒定接触角（CCA）阶段，到混合阶段。在乙醇 - 水二元液滴蒸发过程中，由于沿八边形润湿区域的两个不同对称轴方向的各向异性脱钉，在CCL和CCA阶段之间发现了一个额外的混合阶段。随着乙醇浓度的增加，图案化表面上的液滴脱钉更早发生。
