Karapetsas George, Sahu Kirti Chandra, Sefiane Khellil, Matar Omar K
Department of Mechanical Engineering, University of Thessaly , Volos 38334, Greece.
Langmuir. 2014 Apr 22;30(15):4310-21. doi: 10.1021/la5002682. Epub 2014 Apr 11.
We study the thermocapillary-driven spreading of a droplet on a nonuniformly heated substrate for fluids associated with a non-monotonic dependence of the surface tension on temperature. We use lubrication theory to derive an evolution equation for the interface that accounts for capillarity and thermocapillarity. The contact line singularity is relieved by using a slip model and a Cox-Voinov relation; the latter features equilibrium contact angles that vary depending on the substrate wettability, which, in turn, is linked to the local temperature. We simulate the spreading of droplets of fluids whose surface tension-temperature curves exhibit a turning point. For cases wherein these turning points correspond to minima, and when these minima are located within the droplet, then thermocapillary stresses drive rapid spreading away from the minima. This gives rise to a significant acceleration of the spreading whose characteristics resemble those associated with the "superspreading" of droplets on hydrophobic substrates. No such behavior is observed for cases in which the turning point corresponds to a surface tension maximum.
我们研究了与表面张力对温度具有非单调依赖性的流体在非均匀加热基板上由热毛细作用驱动的液滴铺展情况。我们使用润滑理论来推导一个考虑了毛细作用和热毛细作用的界面演化方程。通过使用滑移模型和考克斯 - 沃伊诺夫关系来消除接触线奇异性；考克斯 - 沃伊诺夫关系的特征是平衡接触角会根据基板的润湿性而变化，而润湿性又与局部温度相关。我们模拟了表面张力 - 温度曲线呈现转折点的流体液滴的铺展情况。对于这些转折点对应最小值且这些最小值位于液滴内部的情况，热毛细应力会驱动液滴从最小值处快速铺展。这导致铺展显著加速，其特征类似于液滴在疏水基板上的“超铺展”现象。而对于转折点对应表面张力最大值的情况，则未观察到这种行为。
