Feng Yijun, Liu Guohua, Xu Jinliang, Wang Kaiying, Mao Wenbin, Yao Guansheng
Beijing Key Laboratory of Multiphase Flow and Heat Transfer for Low Grade Energy Utilization, North China Electric Power University, Beijing 102206, P.R. China.
Department of Microsystems, University of South-Eastern Norway, Horten 3184, Norway.
Langmuir. 2022 Feb 15;38(6):2055-2065. doi: 10.1021/acs.langmuir.1c02994. Epub 2022 Feb 4.
Particle separation from fluid interfaces is one of the major challenges due to the large capillary energy associated with particle adsorption. Previous approaches rely on physicochemical modification or tuning the electrostatic action. Here, we show experimentally that particle separation can be achieved by fast dynamics of drop impact on soap films. When a droplet wrapped with particles (liquid marble) collides with a soap film, it undergoes bouncing and coalescence, stripping and viscous separation, or tunneling through the film. Despite the violence of splashing events, the process robustly yields the stripping in a tunable range. This viscous separation is supported by the transfer front of dynamic contact among the film, particle crust, and drop and can be well controlled in a deterministic manner by selectable impact parameters. By extensive experiments, together with thermodynamic analysis, we disclose that the separation thresholds depend on the energy competition between the kinetic energy, the increased surface energy, and the viscous dissipation. The mechanical cracking of the particle crust arises from the complex coupling between interfacial stress and viscous forces. This study is of potential benefit in soft matter research and also permits the study of a drop with colloid and surface chemistry.
由于与颗粒吸附相关的巨大毛细能，从流体界面分离颗粒是主要挑战之一。以往的方法依赖于物理化学改性或调节静电作用。在此，我们通过实验表明，颗粒分离可以通过液滴撞击肥皂膜的快速动力学来实现。当包裹着颗粒的液滴（液滴弹）与肥皂膜碰撞时，它会经历弹跳和聚结、剥离和粘性分离，或者穿过薄膜。尽管有飞溅事件的剧烈性，但该过程在可调范围内能可靠地产生剥离。这种粘性分离由薄膜、颗粒外壳和液滴之间动态接触的转移前沿所支持，并且可以通过可选择的撞击参数以确定性的方式得到很好的控制。通过广泛的实验以及热力学分析，我们揭示分离阈值取决于动能、增加的表面能和粘性耗散之间的能量竞争。颗粒外壳的机械破裂源于界面应力和粘性力之间的复杂耦合。这项研究在软物质研究中具有潜在益处，并且还允许对具有胶体和表面化学性质的液滴进行研究。
