The ability to control the configuration of a droplet evaporating on a solid surface is important for a wide range of applications, such as printing, coating, micro-patterning, and heat transfer.
Here we study the quasi-static evaporation of 2-dimensional droplets on solid surfaces patterned with a smooth continuous variation of topography or surface chemistry. Using a free-energy approach and a diffuse interface hydrodynamic model, we study the set of equilibrium configurations of the droplet in a parameter space comprising the droplet base radius, cross-sectional area and position relative to the solid pattern. On periodic symmetric patterns, droplets undergo a series of bifurcations that lead to “snap” events. Introducing asymmetry in the patterns leads to a biased lateral motion.
Our results demonstrate the possibility of directed droplet motion on smooth, pinning-free surfaces using the combination of an engineered chemical pattern and a variation of the droplet’s mass induced by a phase change.
Rodrigo Ledesma-Aguilar is a Senior Lecturer in Surfaces and Wetting and member of the Institute for Multiscale Thermofluids at the University of Edinburgh. He did his undergraduate degree in Chemical Engineering at the National Autonomous University of Mexico and his PhD in Physics at the University of Barcelona. He worked as a Marie Curie Fellow at the Rudolph Peierls Centre for Theoretical Physics at the University of Oxford and associate professor at Northumbria University before taking up his current post at Edinburgh. His research interests are in the fluid mechanics of capillarity and wetting, with an interest in their application to smart surfaces.