Drops on polymer brushes -- advances in thin-film modelling of adaptive substrates

TL;DR

This paper reviews recent hydrodynamic models for droplet dynamics on adaptive polymer brush-covered substrates, highlighting advances in modeling volatile and nonvolatile liquids with applications to spreading and sliding behaviors.

Contribution

It introduces and extends mesoscopic hydrodynamic models to include multiple degrees of freedom and volatile liquids on polymer brush substrates.

Findings

Models successfully describe natural and forced spreading of nonvolatile drops.

Models capture sliding behavior of drops on inclined brush-covered surfaces.

Extensions to volatile liquids demonstrate broader applicability.

Abstract

We briefly review recent advances in the hydrodynamic modeling of the dynamics of droplets on adaptive substrates, in particular, solids that are covered by polymer brushes. Thereby, the focus are long-wave and full-curvature variants of mesoscopic hydrodynamic models in gradient dynamics form. After introducing the approach for films/drops of nonvolatile simple liquids on rigid smooth solid substrate, it is first expanded to an arbitrary number of coupled degrees of freedom, before considering the specific case of drops of volatile liquids on brush-covered solids. After presenting the model its usage is illustrated by briefly considering the natural and forced spreading of drops of nonvolatile liquids on a horizontal brush-covered substrate as well as drops sliding down a brush-covered incline. Finally, also volatile liquids are considered.