Department of Chemical Engineering, Graduate School of Engineering, Kyushu University, Motooka 744, Fukuoka 819-0395 Japan.
Langmuir. 2010 Mar 16;26(6):3923-8. doi: 10.1021/la903245m.
In a previous report where internal flows were experimentally visualized in polymer solution droplets receding on a lyophobic surface [Kaneda et al., Langmuir 2008, 24, 9102-9109], the direction of the circulation flow was found to depend on solvent and solute concentration. To identify the reason for this finding, the internal flow in the droplet is investigated numerically. A mathematical model predicts that double circulation flows initiate after a single flow develops at high Marangoni numbers, while only a single circulation flow develops at low Marangoni numbers. The dependencies of the calculated velocities on the solvent and the initial solute concentration agree qualitatively with experiment. It is concluded that the difference of the flow directions that were investigated experimentally is due to such a change in the flow structures. The effects of the contact angle and dimensions on transport phenomena in a droplet are also discussed.
在之前的一份报告中，我们通过实验观察了在疏液表面上后退的聚合物溶液液滴中的内流[Kaneda 等人，Langmuir 2008, 24, 9102-9109]，发现循环流的方向取决于溶剂和溶质浓度。为了找出这一发现的原因，我们对液滴中的内流进行了数值研究。数学模型预测，在高马兰戈尼数下，单流发展后会出现双循环流，而在低马兰戈尼数下只会出现单循环流。计算得到的速度与溶剂和初始溶质浓度的关系与实验定性一致。由此可以得出结论，实验中观察到的流动方向的差异是由于流动结构的这种变化引起的。文中还讨论了接触角和尺寸对液滴内输运现象的影响。
