Metastable wetting

TL;DR

This paper investigates the thermodynamics and dynamics of droplet wetting on grooved substrates, analyzing free energy landscapes, coexistence, and transition times between wet and dry states using both thermodynamic and microscopic models.

Contribution

It introduces a detailed analysis of wetting transitions, including coexistence and metastability, using a combination of thermodynamic calculations and the SOS microscopic model.

Findings

Coexistence of wet and dry states at certain parameters.

Transition times grow exponentially with the free energy barrier.

Transition times follow an exponential-like distribution.

Abstract

Consider a droplet of liquid on top of a grooved substrate. The wetting or not of a groove implies the crossing of a potential barrier as the interface has to distort, to hit the bottom of the groove. We start with computing the free energies of the dry and wet states in the context of a simple thermodynamical model before switching to a random microscopic version pertaining to the Solid-on-Solid (SOS) model. For some range in parameter space (Young angle, pressure difference, aspect ratio), the dry and wet states both share the same free energy, which means coexistence. We compute these coexistence lines together with the metastable regions. In the SOS case, we describe the dynamic transition between coexisting states in wetting. We show that the expected time to switch from one state to the other grows exponentially with the free energy barrier between the stable states and the saddle state, proportional to the groove's width. This random time appears to have an exponential-like distribution.