Characteristic interfacial structure behind a rapidly moving contact line

TL;DR

This paper reveals characteristic interfacial structures behind a rapidly moving contact line, showing that existing theories neglect transverse instabilities which are crucial for understanding forced wetting phenomena.

Contribution

It uncovers the detailed interfacial structures and highlights the importance of transverse instabilities in forced wetting, challenging existing theoretical models.

Findings

Identification of flat triangular interfacial structures

Structures depend on viscosity and velocity

Structures are robust across geometries

Abstract

In forced wetting, a rapidly moving surface drags with it a thin layer of trailing fluid as it is plunged into a second fluid bath. Using high-speed interferometry, we find characteristic structure in the thickness of this layer with multiple thin flat triangular structures separated by much thicker regions. These features, depending on liquid viscosity and penetration velocity, are robust and occur in both wetting and de-wetting geometries. Their presence clearly shows the inadequacy of theoretical analysis that ignores the instability in the transverse direction.