Capillary Fluctuations and Film-Height-Dependent Surface Tension of an Adsorbed Liquid Film

TL;DR

This study investigates capillary wave fluctuations in adsorbed liquid films, revealing a film-thickness-dependent surface tension and a new broadening mechanism, thereby testing and extending the capillary wave Hamiltonian model.

Contribution

It provides the first experimental validation of the interface potential from capillary wave spectra and uncovers a novel film-thickness-dependent surface tension effect.

Findings

Capillary wave spectrum matches interface potential from thermodynamic integration.

Surface tension oscillates with film thickness, indicating a new broadening mechanism.

Validated the capillary wave Hamiltonian for adsorbed liquids with van der Waals forces.

Abstract

Our understanding of both structure and dynamics of adsorbed liquids heavily relies on the capillary wave Hamiltonian, but a thorough test of this model is still lacking. Here we study the capillary wave fluctuations of a liquid film with short range forces adsorbed on a solid exhibiting van der Waals interactions. We show for the first time that the measured capillary wave spectrum right above the first order wetting transition provides an interface potential consistent with independent calculations from thermodynamic integration. However, the surface tension exhibits an oscillatory film thick dependence which reveals a hitherto unnoticed capillary wave broadening mechanism beyond mere interfacial displacements.