Droplet Memory on Liquid-Infused Surfaces

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 nanostruc-tures. 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.

Automated summary

In this work, the friction experienced by water droplets on liquid-infused surfaces (LIS) with both random and regular nanostructures is studied. It is found that consecutive droplets show a memory effect with an increasing velocity up to a plateau value after a certain time. The low-friction trace created by moving droplets in their wake is observed and attributed to the temporary smoothing out of the conformal lubricant layer by a liquid film deposition.