Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
Langmuir. 2023 May 2;39(17):6160-6168. doi: 10.1021/acs.langmuir.3c00289. Epub 2023 Apr 17.
The knowledge of droplet friction on liquid-infused surfaces (LIS) is of paramount importance for applications involving liquid manipulation. While the possible dissipation mechanisms are well-understood, the effect of surface texture has thus far been mainly investigated on LIS with highly regular solid topographies. In this work, we aim to address this experimental gap by studying the friction experienced by water droplets on LIS based on both random and regular polysilsesquioxane nanostructures. We show that the available models apply to the tested surfaces, but we observe a previously unreported droplet memory effect: as consecutive droplets travel along the same path, their velocity increases up to a plateau value before returning to the original state after a sufficiently long time. We study the features of this phenomenon by evaluating the motion of droplets when they cross the path of a previous sequence of droplets, discovering that moving droplets create a low-friction trace in their wake, whose size matches their base diameter. Finally, we attribute this to the temporary smoothing out of an initially conformal lubricant layer by means of a Landau-Levich-Derjaguin liquid film deposition behind the moving droplet. The proposed mechanism might apply to any LIS with a conformal lubricant layer.
液滴在液体浸润表面（LIS）上的摩擦知识对于涉及液体操纵的应用至关重要。虽然已经很好地理解了可能的耗散机制，但迄今为止，表面纹理的影响主要是在具有高度规则固体形貌的 LIS 上进行研究。在这项工作中，我们旨在通过研究基于随机和规则聚硅倍半氧烷纳米结构的 LIS 上的水滴摩擦来解决这一实验差距。我们表明，可用的模型适用于测试表面，但我们观察到了以前未报道的液滴记忆效应：当连续的液滴沿相同路径行进时，它们的速度会增加到一个平台值，然后在足够长的时间后返回原始状态。我们通过评估当液滴穿过先前液滴序列的路径时的运动来研究这种现象的特征，发现移动的液滴在其尾迹中会产生低摩擦痕迹，其大小与它们的基底直径相匹配。最后，我们将其归因于移动液滴后面的 Landau-Levich-Derjaguin 液体膜沉积暂时抚平了初始的共形润滑剂层。所提出的机制可能适用于任何具有共形润滑剂层的 LIS。
