Sen Uddalok, Chatterjee Souvick, Ganguly Ranjan, Dodge Richard, Yu Lisha, Megaridis Constantine M
Department of Mechanical and Industrial Engineering, University of Illinois at Chicago , Chicago, Illinois 60607, United States.
Department of Power Engineering, Jadavpur University , Kolkata 700098, India.
Langmuir. 2018 Feb 6;34(5):1899-1907. doi: 10.1021/acs.langmuir.7b03896. Epub 2018 Jan 22.
Spontaneous pumpless transport of droplets on wettability-confined tracks is important for various applications, such as rapid transport and mixing of fluid droplets, enhanced dropwise condensation, biomedical devices, and so forth. Recent studies have shown that on an open surface, a superhydrophilic track of diverging width, laid on a superhydrophobic background, facilitates the transport of water from the narrower end to the wider end at unprecedented rates (up to 40 cm/s) without external actuation. The spreading behavior on such surfaces, however, has only been characterized for water. Keeping in mind that such designs play a key role for a diverse range of applications, such as handling organic liquids and in point-of-care devices, the importance of characterizing the spreading behavior of viscous liquids on such surfaces cannot be overemphasized. In the present work, the spreading behavior on the aforementioned wettability-patterned diverging tracks was observed for fluids of different viscosities. Two dimensionless variables were identified, and a comprehensive relationship was obtained. Three distinct temporal regimes of droplet spreading were established: I), a Washburn-type slow spreading, II) a much faster Laplace pressure-driven spreading, and III), a sluggish density-augmented Tanner-type film spreading. The results offer design guidance for tracks that can pumplessly manage fluids of various viscosities and surface tensions.
液滴在润湿性受限轨道上的自发无泵输运对于各种应用都很重要，例如液滴的快速输运与混合、强化滴状冷凝、生物医学设备等等。最近的研究表明，在开放表面上，铺设在超疏水背景上的宽度发散的超亲水轨道，能够在无外部驱动的情况下以前所未有的速率（高达40厘米/秒）促进水从较窄端向较宽端的输运。然而，此类表面上的铺展行为仅针对水进行了表征。鉴于此类设计在诸如处理有机液体和即时检测设备等多种应用中起着关键作用，表征粘性液体在此类表面上的铺展行为的重要性再怎么强调也不为过。在本工作中，观察了不同粘度流体在上述润湿性图案化发散轨道上的铺展行为。确定了两个无量纲变量，并得到了一个全面的关系。建立了液滴铺展的三个不同时间阶段：I），沃什伯恩型缓慢铺展，II），快得多的拉普拉斯压力驱动铺展，以及III），缓慢的密度增强坦纳型薄膜铺展。这些结果为能够无泵管理各种粘度和表面张力流体的轨道提供了设计指导。
