Long-time Evolution of Interfacial Structure of Partial Wetting

TL;DR

This study investigates the long-term behavior of interfacial structures during partial wetting and forced wetting, revealing scaling laws and new phenomena not captured by existing models.

Contribution

It introduces a novel optical measurement technique and provides systematic analysis of steady-state interfacial structures during wetting and dewetting.

Findings

Interfacial layer thickness scales with capillary number Ca.

Alternating thin and thick regions are observed in steady state.

A new interfacial region appears during onset, differing from previous models.

Abstract

When a solid plate is withdrawn from a partially wetting liquid, a liquid layer dewets the moving substrate. High-speed imaging reveals alternating thin and thick regions in the entrained layer in the transverse direction at steady state. This paper systematically compares this situation to the reversed process, forced wetting, where a solid entrains an air layer along its surface as it is pushed into a liquid. To quantify the absolute thickness of these steady-state structures precisely, I have developed an optical technique, taking advantage of the angle dependence of interference, combined with a method based on a maximum likelihood estimation. The data show that the thicknesses of both regions of the film scale with the capillary number, Ca. In addition, a new region is observed during onset which differs from the behavior predicted by previous models.