SPP 2171 - Subproject: Ensembles of sitting and sliding drops on elastic media - experiment, simulation and theory

Basic data for this project

Description

Droplets on soft elastic substrates are a paradigmatic example of adaptive wetting, where capillarity-induced elastic deformations dramatically affect the wetting properties. Recent work has shown that substrates made from cross-linked polymer networks offer versatile routes to manipulate contact angles of droplets, as well as their spreading, directed motion, condensation and splashing. However, the full richness of these phenomena is only beginning to be explored and at present there is even no fully quantitative understanding of the behaviour of single drops -- let alone ensembles of drops. Key challenges lie in the intricate effects of solid surface tension, and how this affects the force balance near the contact line, while dynamics involves viscoelasticy of the substrate and elastocapillary interactions between droplets.This project aims at developing and utilising experimental setups, detailed direct numerical simulations, effective long-wave models and a Smoluchowski-type statistical description to investigate the behaviour of drops of simple nonvolatile and volatile liquids on flexible substrates. The first part of the project focusses on single drops. We wish to go beyond the current approaches that are almost exclusively based on linear elasticity, and develop detailed simulations that reveal the large-deformation mechanics near the contact line. The goal is a first-principles fully quantitive description of the wetting behaviour of single drops. This will form the basis for the second part of the project, where we will investigate the collective behaviour of ensembles of drops on soft substrates. Experiments on droplet ensembles, driven by external forcing or evaporation-condensation, will be complemented by a multi-scale modelling approach where we resolve the dynamics on different levels of detail. We develop effective long-wave models that are calibrated from the experimental and full simulation results for single drops, which opens the way for simulations of a large number of droplets, and ultimately for statistical modelling of drop ensembles.The consistent combination of experiment, simulation and theory offers a multi-scale framework that provides qualitative and quantitative insights into the wetting of flexible substrates. It will reveal the interplay of drop and substrate dynamics, and the emergent laws of sliding, stick-slip motion and coalescence of individual drops and their collective ensemble behaviour.