Liquid film dynamics with immobile contact line during meniscus oscillation

TL;DR

This paper provides a theoretical analysis of liquid film dynamics during meniscus oscillation in a capillary, considering a pinned contact line and evaporation effects, with results compared to experimental data.

Contribution

It introduces a model for oscillating meniscus with an immobile contact line, incorporating film variation, contact angle dynamics, and evaporation effects, extending previous steady-state analyses.

Findings

Average film thickness depends on initial contact angle.

Numerical results align with experimental data.

Superheating can prevent contact line pinning during oscillations.

Abstract

This paper presents a theoretical analysis of the liquid film dynamics during the oscillation of a meniscus between a liquid and its vapour in a cylindrical capillary. By using the theory of Taylor bubbles, the dynamic profile of the deposited liquid film is calculated within the lubrication approximation accounting for the finiteness of the film length, i.e. for the presence of the contact line. The latter is assumed to be pinned on a surface defect and thus immobile; the contact angle is allowed to vary. The fluid flow effect on the curvature in the central meniscus part is neglected. This curvature varies in time because of the film variation and is determined as a part of the solution. The film dynamics depends on the initial contact angle, which is the maximal contact angle attained during oscillation. The average film thickness is studied as a function of system parameters. The numerical results are compared to existing experimental data and to the results of the quasi-steady approximation. Finally, the problem of an oscillating meniscus is considered accounting for the superheating of the capillary wall with respect to the saturation temperature, which causes evaporation. When the superheating exceeds a quite low threshold, oscillations with a pinned contact line are impossible and the contact line recession caused by evaporation needs to be accounted for.