Quantifying density fluctuations in water at a hydrophobic surface: evidence for critical drying

TL;DR

This study uses advanced Monte Carlo simulations to analyze water density fluctuations near hydrophobic surfaces, providing evidence for a critical drying transition that enhances local density variability.

Contribution

It introduces a rigorous measure of local compressibility and demonstrates a continuous drying transition as substrate-water attraction weakens.

Findings

Density fluctuations increase near hydrophobic surfaces

Evidence for a critical drying transition as attraction weakens

Enhanced density fluctuations linked to critical drying hypothesis

Abstract

Employing smart Monte Carlo sampling techniques within the grand canonical ensemble, we investigate the properties of water at a model hydrophobic substrate. By reducing the strength of substrate-water attraction we find that fluctuations in the local number density, quantified by a rigorous definition of the local compressibility $\chi(z)$, increase rapidly for distances $z$ within $1$ or $2$ molecular diameters from the substrate as the degree of hydrophobicity, measured by the macroscopic contact angle $\theta$, increases. Our simulations provide evidence for a continuous (critical) drying transition as the substrate-water interaction becomes very weak: $\cos(\theta)\to -1$. We speculate that the existence of such a transition might account for earlier simulation observations of strongly enhanced density fluctuations.