Weakly charged droplets fundamentally change impact dynamics on flat surfaces
Weakly charged droplets fundamentally change impact dynamics on flat surfaces
复制标题
弱带电液滴从根本上改变了平面上的撞击动力学
DOI：
10.1039/c9sm00895k
复制
发表时间：
2019-07-28
期刊：
影响因子：
3.4
通讯作者：
Deng, Weiwei
中科院分区：
文献类型：
--
作者：
Gao, Fan;Yi, Hao;Deng, Weiwei
电荷通常存在于自然或人工形成的水滴中，如雨滴和开尔文滴水器产生的水滴。与中性液滴撞击在平坦的固体表面上形成薄的凸透镜形状的气体薄膜不同，我们表明，即使是弱带电的液滴，微妙的气体薄膜也可以从根本上改变。当电荷水平高于典型撞击条件下瑞利极限的1%的临界水平时，Maxwell应力克服了气体压力积累，使液滴底部表面变形。锥形液体尖端形成并穿透气膜，导致一条圆形接触线向外移动，不会捕获任何气体。临界电荷水平仅取决于基于气体粘度的毛细管数。这一发现适用于普通液体和熔融合金液滴，为一系列应用提供了新的见解，例如减轻添加剂制造中的针孔缺陷。
Electric charges are often found in naturally or artificially formed droplets, such as raindrops and those generated by Kelvin's water dropper. In contrast to the impact of neutral droplets on a flat solid surface upon which a thin convex lens shape layer of the gas film is typically formed, we show that the delicate gas thin film can be fundamentally altered for even weakly charged droplets. As the charge level is raised above a critical level of similar to 1% of the Rayleigh limit for representative impact conditions, the Maxwell stress overcomes the gas pressure buildup to deform the droplet bottom surface. A conical liquid tip forms and pierces through the gas film, leading to a circular contact line moving outwards that does not trap any gas. The critical charge level only depends on the capillary number based on the gas viscosity. This finding applies to common liquids and molten alloy droplets, providing new insights into a range of applications such as mitigating pinhole defects in additive manufacturing.