Pelizzari Michele, McHale Glen, Armstrong Steven, Zhao Hongyu, Ledesma-Aguilar Rodrigo, Wells Gary G, Kusumaatmaja Halim
Institute for Multiscale Thermofluids, School of Engineering, The University of Edinburgh, Edinburgh EH9 3FB, U.K.
Department of Physics, Durham University, Durham DH1 3LE, U.K.
Langmuir. 2023 Nov 7;39(44):15676-15689. doi: 10.1021/acs.langmuir.3c02205. Epub 2023 Oct 24.
Young's equation is fundamental to the concept of the wettability of a solid surface. It defines the contact angle for a droplet on a solid surface through a local equilibrium at the three-phase contact line. Recently, the concept of a liquid Young's law contact angle has been developed to describe the wettability of slippery liquid-infused porous surfaces (SLIPS) by droplets of an immiscible liquid. In this work, we present a new method to fabricate biphilic SLIP surfaces and show how the wettability of the composite SLIPS can be exploited with a macroscopic wedge-shaped pattern of two distinct lubricant liquids. In particular, we report the development of composite liquid surfaces on silicon substrates based on lithographically patterning a Teflon AF1600 coating and a superhydrophobic coating (Glaco Mirror Coat Zero), where the latter selectively dewets from the former. This creates a patterned base surface with preferential wetting to matched liquids: the fluoropolymer PTFE with a perfluorinated oil Krytox and the hydrophobic silica-based GLACO with olive oil (or other mineral oils or silicone oil). This allows us to successively imbibe our patterned solid substrates with two distinct oils and produce a composite liquid lubricant surface with the oils segregated as thin films into separate domains defined by the patterning. We illustrate that macroscopic wedge-shaped patterned SLIP surfaces enable low-friction droplet self-propulsion. Finally, we formulate an analytical model that captures the dependence of the droplet motion as a function of the wettability of the two liquid lubricant domains and the opening angle of the wedge. This allows us to derive scaling relationships between various physical and geometrical parameters. This work introduces a new approach to creating patterned liquid lubricant surfaces, demonstrates long-distance droplet self-propulsion on such surfaces, and sheds light on the interactions between liquid droplets and liquid surfaces.
杨氏方程是固体表面润湿性概念的基础。它通过三相接触线上的局部平衡来定义固体表面上液滴的接触角。最近，液体杨氏定律接触角的概念已被提出，用于描述不相溶液体的液滴对光滑液体注入多孔表面（SLIPS）的润湿性。在这项工作中，我们提出了一种制造双亲性SLIP表面的新方法，并展示了如何利用两种不同润滑液的宏观楔形图案来开发复合SLIPS的润湿性。特别是，我们报告了基于光刻图案化聚四氟乙烯AF1600涂层和超疏水涂层（Glaco Mirror Coat Zero）在硅基板上开发复合液体表面的过程，其中后者会选择性地从前者上脱湿。这创造了一个对匹配液体具有优先润湿性的图案化基底表面：含全氟油Krytox的含氟聚合物聚四氟乙烯以及含橄榄油（或其他矿物油或硅油）的疏水性二氧化硅基GLACO。这使我们能够依次用两种不同的油浸润我们的图案化固体基板，并产生一种复合液体润滑表面，其中油以薄膜形式分离到由图案定义的不同区域中。我们表明宏观楔形图案化的SLIP表面能够实现低摩擦液滴自推进。最后，我们建立了一个分析模型，该模型捕捉了液滴运动与两种液体润滑区域的润湿性以及楔形开口角度之间的依赖关系。这使我们能够推导出各种物理和几何参数之间的比例关系。这项工作引入了一种创建图案化液体润滑表面的新方法，展示了在此类表面上的长距离液滴自推进，并阐明了液滴与液体表面之间的相互作用。
