Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry and Environment, Beihang University , Beijing 100191, China.
Langmuir. 2017 Nov 28;33(47):13480-13489. doi: 10.1021/acs.langmuir.7b03087. Epub 2017 Nov 14.
Liquid transport is a fundamental process relevant to a wide range of applications, for example, heat transfer, anti-icing, self-cleaning, drag reduction, and microfluidic systems. For these applications, a deeper understanding of the sliding behavior of water droplets on solid surfaces is of particular importance. In this study, the frictional behavior of water droplets sliding on superhydrophobic surfaces decorated with micropillar arrays was studied using a nanotribometer. Our experiments show that surfaces with a higher solid area fraction generally exhibited larger friction, although friction might drop when the solid area fraction was close to unity. More interestingly, we found that the sliding friction of droplets was enhanced when the dimension of the microstructures increased, showing a distinct size effect. The nonmonotonic dependence of friction force on solid area fraction and the apparent size effect can be qualitatively explained by the evolution of two governing factors, that is, the true length of the contact line and the coordination degree of the depinning events. The mechanisms are expected to be generally applicable for other liquid transport processes involving the dynamic motion of a three-phase contact line, which may provide a new means of tuning liquid-transfer behavior through surface microstructures.
液体输运是一个与广泛应用相关的基本过程，例如传热、防冰、自清洁、减阻和微流系统。对于这些应用，深入了解液滴在固体表面上的滑动行为尤为重要。在这项研究中，我们使用纳米摩擦仪研究了具有微柱阵列装饰的超疏水表面上液滴滑动的摩擦行为。我们的实验表明，固体面积分数较高的表面通常表现出较大的摩擦力，尽管当固体面积分数接近 1 时摩擦力可能会下降。更有趣的是，我们发现当微结构的尺寸增加时，液滴的滑动摩擦力会增强，表现出明显的尺寸效应。摩擦力与固体面积分数的非单调依赖性以及明显的尺寸效应可以通过两个控制因素的演化来定性解释，即真实接触线长度和去钉事件的协调程度。这些机制有望普遍适用于涉及三相接触线动态运动的其他液体输运过程，这可能为通过表面微结构调节液体输运行为提供一种新的手段。
