Microscopic origin of the effect of substrate metallicity on interfacial free energies

TL;DR

This study uses molecular simulations and a new thermodynamic integration method to explore how the metallic nature of substrates influences interfacial free energies, revealing charge correlations as a key microscopic factor.

Contribution

It introduces a novel thermodynamic integration framework combined with a semi-classical model to analyze substrate metallicity effects on interfacial thermodynamics.

Findings

Charge distribution within metals affects interfacial free energy.

The method validates against analytical and experimental contact angle data.

Charge correlations are identified as the microscopic origin of free energy evolution.

Abstract

We investigate the effect of the metallic character of solid substrates on solid-liquid interfacial thermodynamics using molecular simulations. Building on the recent development of a semi-classical Thomas-Fermi model to tune the metallicity in classical molecular dynamics simulations, we introduce a new thermodynamic integration framework to compute the evolution of the interfacial free energy as a function of the Thomas-Fermi screening length. We validate this approach against analytical results for empty capacitors and by comparing the predictions in the presence of an electrolyte with values determined from the contact angle of droplets on the surface. The general expression derived in this work highlights the role of the charge distribution within the metal. We further propose a simple model to interpret the evolution of the interfacial free energy with voltage and Thomas-Fermi length, which allows us to identify the charge correlations within the metal as the microscopic origin of the evolution of the interfacial free energy with the metallic character of the substrate. This new methodology opens the door to the molecular-scale study of the effect of the metallic character of the substrate on confinement-induced transitions in ionic systems, as reported in recent Atomic Force Microscopy and Surface Force Apparatus experiments.