Apparent Contact Angles on Lubricant-Impregnated Surfaces/SLIPS: From Superhydrophobicity to Electrowetting
Apparent Contact Angles on Lubricant-Impregnated Surfaces/SLIPS: From Superhydrophobicity to Electrowetting
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DOI：
10.1021/acs.langmuir.8b04136
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发表时间：
2019-03-19
期刊：
影响因子：
3.9
通讯作者：
Ledesma-Aguilar, Rodrigo
中科院分区：
文献类型：
--
作者：
McHale, Glen;Orme, Bethany V.;Ledesma-Aguilar, Rodrigo
液体在许多表面上的一个基本限制是它们的接触线钉扎。通过将非挥发性和不混溶的液体或润滑剂注入在固体衬底中产生或施加到固体衬底上的纹理或粗糙度中，从而使感兴趣的液体不再直接接触下表面，可以克服这一限制。这种光滑的注入液体的多孔表面(卡瓦)，也被称为浸渍润滑剂的表面，完全消除了接触线钉扎和接触角滞后。然而，尽管固着液滴可能停留在这样的表面上，但它的接触角只能是一个表观接触角，因为它现在与第二个液体而不是固体接触。在靠近固体的地方，液滴有一个润湿脊，液-液和液-汽界面张力的力平衡由诺伊曼三角而不是杨定律描述。在这里，我们展示了在润滑剂涂层薄且润湿脊小的情况下，如何使用表面自由能方法来获得类似于杨氏定律的表观接触角方程，并利用润滑剂-蒸气和液体-润滑剂的界面张力以及液体-润滑剂-蒸气组合界面的有效界面张力。对于润滑剂在液体上的正扩散和负扩散，该有效界面张力分别是液体-润滑剂和润滑剂-汽相界面张力或气液界面张力之和。通过这种方法，我们展示了对于粗糙的、纹理的或复杂的几何表面以及电润湿和介电润湿，如何使用Cassie-Baxter、Wenzel、半芯和其他方程，用等效光滑的浸渍润滑剂的表面的表观接触角代替杨氏定律接触角。所得方程与文献数据吻合较好。这些结果使得固着液滴在表面上的平衡接触角理论能够广泛地应用于保持薄层和保形涂层的表面。
A fundamental limitation of liquids on many surfaces is their contact line pinning. This limitation can be overcome by infusing a nonvolatile and immiscible liquid or lubricant into the texture or roughness created in or applied onto the solid substrate so that the liquid of interest no longer directly contacts the underlying surface. Such slippery liquid-infused porous surfaces (SLIPS), also known as lubricant-impregnated surfaces, completely remove contact line pinning and contact angle hysteresis. However, although a sessile droplet may rest on such a surface, its contact angle can be only an apparent contact angle because its contact is now with a second liquid and not a solid. Close to the solid, the droplet has a wetting ridge with a force balance of the liquid-liquid and liquid-vapor interfacial tensions described by Neumann's triangle rather than Young's law. Here, we show how, provided the lubricant coating is thin and the wetting ridge is small, a surface free energy approach can be used to obtain an apparent contact angle equation analogous to Young's law using interfacial tensions for the lubricant-vapor and liquid-lubricant and an effective interfacial tension for the combined liquid-lubricant-vapor interfaces. This effective interfacial tension is the sum of the liquid-lubricant and the lubricant-vapor interfacial tensions or the liquid-vapor interfacial tension for a positive and negative spreading power of the lubricant on the liquid, respectively. Using this approach, we then show how Cassie-Baxter, Wenzel, hemiwicking, and other equations for rough, textured or complex geometry surfaces and for electrowetting and dielectrowetting can be used with the Young's law contact angle replaced by the apparent contact angle from the equivalent smooth lubricant-impregnated surface. The resulting equations are consistent with the literature data. These results enable equilibrium contact angle theory for sessile droplets on surfaces to be used widely for surfaces that retain a thin and conformal SLIPS coating.