# Wetting and dewetting processes in the axial retraction of liquid filaments

## TL;DR

This paper investigates the hydrodynamics of liquid filament retraction on a substrate, emphasizing contact angle hysteresis effects, through experiments, hybrid wettability theory, and numerical simulations, relevant for laser-induced dewetting applications.

## Contribution

It combines experimental observations, a hybrid wettability model, and numerical simulations to analyze filament retraction dynamics under partial wetting conditions, incorporating contact angle hysteresis effects.

## Key findings

- Contact angle hysteresis significantly influences filament breakup.
- The hybrid wettability model accurately predicts the retraction behavior.
- Numerical simulations align well with experimental results.

## Abstract

We study the hydrodynamic mechanisms involved in the motion of the contact line formed at the end region of a liquid filament laying on a planar and horizontal substrate. Since the flow develops under partially wetting conditions, the tip of the filament recedes and forms a bulged region (head), that subsequently develops a neck region behind it. Later on, the neck breaks up leading to a separated drop, while the rest of the filament restarts the sequence. One main feature of this flow is that the whole dynamics and final drop shapes are strongly influenced by the hysteresis of the contact angle typical in most of the liquid/substrate systems. The time evolution till breakup is studied experimentally and pictured in terms of a hybrid wettability theory which involves the Cox-Voinov hydrodynamic approach combined with the molecular kinetic theory developed by Blake. The parameters of this theory are determined for our liquid/substrate system (silicon oil / coated glass). The experimental results of the retracting filament are described in terms of a simple heuristic model, and also compared with numerical simulations of the full Navier-Stokes equations. This study is of special interest in the context of pulsed laser induce dewetting (PLiD).