Probing wetting properties with self-propelled droplets

Abstract

When a drop of water is placed on a rough surface, several wetting regimes can occur. The droplet may remain in a dry state, with air pockets trapped underneath, or it may enter a wet state, characterized by homogeneous wetting of the surface. A common feature of this phenomenon is meta-stability: the steady states of the droplet can vary depending on its initial deposition. The search for those equilibrium points, for a given roughness, has many technological applications, such as self-cleaning surfaces. However, it is experimentally and computationally difficult to approach this problem, since it requires many trials to find all stable states. A potential approach to addressing this challenge involves leveraging the principles and methods of active matter. In this study, we employ numerical simulations using a 3D Potts model to investigate how the incorporation of self-propulsion into a well-established wetting scenario can provide insights into the metastable properties of a given surface. As a result we show that, for certain roughness, activity can be tuned to maintain the droplet in a specific range of local minima or even extinguish the meta-stable behavior. In all cases examined, a rise in self-propulsion resulted in a decrease in the disparity between the driest and wettest minima. This indicates that the proposed method can be effectively used to: i) assess whether a substrate exhibits metastability; ii) estimate the number of local minima on a substrate while simultaneously measuring the associated contact angles; and iii) provide an indication of the surface’s contact angle hysteresis.