Wetting and cavitation pathways on nanodecorated surfaces

TL;DR

This study uses molecular dynamics simulations to explore how nanostructured surfaces resist or facilitate vapor bubble formation and wetting transitions, revealing multiple pathways influenced by surface geometry and pressure conditions.

Contribution

It provides detailed atomistic insights into wetting and cavitation pathways on nanodecorated surfaces, highlighting the role of complex geometries and thermal fluctuations in stability.

Findings

Multiple wetting and cavitation pathways identified

Free energy barriers are around 100 k_B T

Macroscopic theory aligns semi-quantitatively but misses density fluctuations

Abstract

In this contribution we study wetting and nucleation of vapor bubbles on nanodecorated surfaces via free energy molecular dynamics simulations. The results shed light on the stability of superhydrophobicity in submerged surfaces with nanoscale corrugations. The re-entrant geometry of the cavities under investigation is capable of sustaining a confined vapor phase within the surface roughness (Cassie state) both for hydrophobic and hydrophilic combinations of liquid and solid. The atomistic system is of nanometric size; on this scale thermally activated events can play an important role ultimately determining the lifetime of the Cassie state. Such superhydrophobic state can break down by full wetting of the texture at large pressures (Cassie-Wenzel transition) or by nucleating a vapor bubble at negative pressures (cavitation). Specialized rare event techniques show that several pathways for wetting and cavitation are possible, due to the complex surface geometry. The related free energy barriers are of the order of 100 k_B T and vary with pressure. The atomistic results are found to be in semi-quantitative accord with macroscopic capillarity theory. However, the latter is not capable of capturing the density fluctuations, which determine the destabilization of the confined liquid phase at negative pressures (liquid spinodal).