Centre for Nano Science and Engineering, Indian Institute of Science, Bangalore 560012, India.
Soft Matter. 2018 Feb 28;14(9):1571-1580. doi: 10.1039/c7sm02145c.
When a droplet impacts a superhydrophobic sieve, a part of the droplet penetrates through it when the dynamic pressure (ρU) of the impinging droplet exceeds the breakthrough pressure (γΓ/A). At higher impact velocities, the ejected-jet breaks and separates from the main droplet. The remaining part of the droplet bounces off the surface showing different modes (normal bouncing as a vertically elongated drop or pancake bouncing). In this work, we have studied the effect of different geometrical parameters of superhydrophobic copper meshes on different modes of droplet rebound. We observe three different effects in our study. Firstly, we observe pancake like bouncing, which is attributed to the capillary energy of the rebounding interface formed after the breaking of the ejected-jet. Secondly, we observe leakage of the droplet volume and kinetic energy due to the breaking of the ejected-jet, which leads to reduction in the contact times. Finally, we observe that for flexible meshes, the transition to pancake type bouncing is induced at lower Weber numbers. Flexibility also leads to a reduction in the volume loss from the ejected-jet. This study will be helpful in the design of superhydrophobic meshes for use under impact scenarios.
当液滴冲击超疏水筛网时，如果撞击液滴的动压（ρU）超过突破压力（γΓ/A），则部分液滴会穿透筛网。在更高的撞击速度下，喷射射流会断裂并与主液滴分离。液滴的剩余部分会从表面反弹，呈现出不同的模式（垂直拉长的液滴的正常反弹或煎饼状反弹）。在这项工作中，我们研究了超疏水铜网的不同几何参数对液滴反弹不同模式的影响。我们在研究中观察到了三种不同的效应。首先，我们观察到了类似于煎饼的反弹，这归因于喷射射流断裂后形成的反弹界面的毛细能量。其次，我们观察到喷射射流断裂导致液滴体积和动能的泄漏，从而缩短了接触时间。最后，我们观察到对于柔性筛网，在较低的韦伯数下会诱导向煎饼状反弹的转变。柔韧性也会减少喷射射流的体积损失。这项研究将有助于设计用于冲击场景的超疏水筛网。
