Nanoscale fluid structure of liquid-solid-vapour contact lines for a wide range of contact angles

TL;DR

This study investigates the nanoscale fluid structure near contact lines across a wide range of contact angles, revealing that planar computations of disjoining pressure can accurately predict adsorption profiles despite complex three-dimensional effects.

Contribution

It demonstrates that planar Derjaguin-Frumkin disjoining pressure calculations accurately predict adsorption height profiles for all contact angles studied, extending previous findings beyond 90 degrees.

Findings

Normal pressure is softened by the liquid-vapour interface width.

Adsorption film height can be predicted by planar computations.

Two-dimensional effects influence pressure but not height profiles.

Abstract

We study the nanoscale behaviour of the density of a simple fluid in the vicinity of an equilibrium contact line for a wide range of Young contact angles between 40 and 135 degrees. Cuts of the density profile at various positions along the contact line are presented, unravelling the apparent step-wise increase of the film height profile observed in contour plots of the density. The density profile is employed to compute the normal pressure acting on the substrate along the contact line. We observe that for the full range of contact angles, the maximal normal pressure cannot solely be predicted by the curvature of the adsorption film height, but is instead softened -- likely by the width of the liquid-vapour interface. Somewhat surprisingly however, the adsorption film height profile can be predicted to a very good accuracy by the Derjaguin-Frumkin disjoining pressure obtained from planar computations, as was first shown in [Nold et al., Phys. Fluids, 26, 072001, 2014] for contact angles less than 90 degrees, a result which here we show to be valid for the full range of contact angles. This suggests that while two-dimensional effects cannot be neglected for the computation of the normal pressure distribution along the substrate, one-dimensional planar computations of the Derjaguin-Frumkin disjoining pressure are sufficient to accurately predict the adsorption height profile.