Fluid structure in the immediate vicinity of an equilibrium three-phase contact line and assessment of disjoining pressure models using density functional theory

TL;DR

This study uses density functional theory to analyze the nanoscale structure of three-phase contact lines and assesses the accuracy of different disjoining pressure models in predicting the contact line behavior.

Contribution

It compares the effectiveness of two disjoining pressure models against DFT results, highlighting the strengths and limitations of each in predicting contact line profiles.

Findings

Disjoining pressure from adsorption isotherm aligns well with DFT results.

Normal force balance model shows limited agreement with DFT.

Results consistent across contact angles of 20°, 40°, and 60°.

Abstract

We examine the nanoscale behavior of an equilibrium three-phase contact line in the presence of long-ranged intermolecular forces by employing a statistical mechanics of fluids approach, namely density functional theory (DFT) together with fundamental measure theory (FMT). This enables us to evaluate the predictive quality of effective Hamiltonian models in the vicinity of the contact line. In particular, we compare the results for mean field effective Hamiltonians with disjoining pressures defined through (I) the adsorption isotherm for a planar liquid film, and (II) the normal force balance at the contact line. We find that the height profile obtained using (I) shows good agreement with the adsorption film thickness of the DFT-FMT equilibrium density profile in terms of maximal curvature and the behavior at large film heights. In contrast, we observe that while the height profile obtained by using (II) satisfies basic sum rules, it shows little agreement with the adsorption film thickness of the DFT results. The results are verified for contact angles of 20, 40 and 60 degrees.