Controlling the dewetting morphologies of thin liquid films by switchable substrates

TL;DR

This study uses computational modeling to explore how switchable substrates influence the morphology of thin liquid films, revealing conditions for droplet formation and rivulet stability based on substrate wettability dynamics.

Contribution

It introduces a criterion for rivulet formation on switchable substrates and analyzes how pattern wavelength and speed affect film rupture and droplet shapes.

Findings

Rivulets form at high rates of wettability change.

A dimensionless parameter predicts rivulet occurrence.

Rupture times and droplet shapes depend on pattern parameters.

Abstract

Switchable and adaptive substrates emerged as valuable tools for the control of wetting and actuation of droplet motion. Here we report a computational study of the dynamics of an unstable thin liquid film deposited on a switchable substrate, modelled with a space and time varying contact angle. With a static pattern, all the fluid is drained into droplets located around contact angle minima, whereas for a sufficiently large rate of wettability variation a state consisting of metastable rivulets is observed. A criterion discriminating whether rivulets can be observed or not is identified in terms of a single dimensionless parameter. Finally, we show and explain theoretically how the film rupture times, droplet shape and rivulet life time depend on the pattern wavelength and speed.