Department of Mechanical Engineering, University of Massachusetts Amherst, Amherst, MA 01003-2210, United States.
J Colloid Interface Sci. 2011 Nov 15;363(2):646-54. doi: 10.1016/j.jcis.2011.07.086. Epub 2011 Aug 3.
In this work, droplet coalescence and the subsequent mixing in superhydrophobic surfaces is studied over a range of impact velocities and impact angles. Sanded Teflon surfaces are used as a novel two-dimensional microfluidics platform. These superhydrophobic surfaces exhibit a constant advancing contact angle of θ(A)=150° over a broad range of contact angle hysteresis. As a result, the effect of contact angle hysteresis on droplet coalescence and mixing can be studied. Based on the observed characteristics of coalescence, three different regimes of coalescence are identified as a function of both Weber number and impact angle. These regimes include oscillation dominated, rotation dominated, and mixed dynamics. It is shown that within Weber number ranges achievable in this experiment, hysteresis greatly reduces the deformation of the droplet coalescence process and the subsequent mixing. In head-on collisions, higher hysteresis is found to decrease the frequency at which the resulting dr oscillates. In the case of glancing collisions, where the resulting droplet is found to rotate, higher hysteresis increases the rate of rotation although the overall angular momentum is found to be independent of contact angle hysteresis.
在这项工作中，研究了液滴聚并及其在超疏水表面随后的混合过程，涵盖了一系列的冲击速度和冲击角度。磨砂聚四氟乙烯表面被用作一种新颖的二维微流控平台。这些超疏水表面在较宽的接触角滞后范围内表现出恒定的前进接触角θ(A)=150°。因此，可以研究接触角滞后对液滴聚并和混合的影响。根据观察到的聚并特征，根据韦伯数和冲击角度的函数，确定了三种不同的聚并区。这些区包括以振动为主、以旋转为主和混合动力学。结果表明，在所进行的实验中，在可以达到的韦伯数范围内，滞后极大地降低了液滴聚并过程的变形和随后的混合。在正面碰撞中，发现较高的滞后会降低所得液滴 dr 振动的频率。在发生旋转的掠射碰撞的情况下，发现较高的滞后会增加旋转的速率，尽管总的角动量发现与接触角滞后无关。
