Breakup Dynamics of Capillary Bridges on Hydrophobic Stripes

TL;DR

This study investigates the breakup process of a capillary bridge on hydrophobic stripes using combined experimental and numerical methods, revealing complex dynamics and multiple scaling behaviors during breakup.

Contribution

It introduces a novel phase space approach and advanced numerical techniques to analyze capillary bridge breakup on patterned surfaces.

Findings

Breakup dynamics vary across different stages with multiple scaling exponents.

The final breakup stage aligns with Rayleigh-Plateau instability.

Numerical methods improve stability and realism of simulations.

Abstract

The breakup dynamics of a capillary bridge on a hydrophobic stripe between two hydrophilic stripes is studied experimentally and numerically using direct numerical simulations. The capillary bridge is formed from an evaporating water droplet wetting three neighboring stripes of a chemically patterned surface. By considering the breakup process in a phase space representation, the breakup dynamics can be evaluated without the uncertainty in determining the precise breakup time. The simulations are based on the Volume-of-Fluid (VOF) method implemented in Free Surface 3D (FS3D). In order to construct physically realistic initial data for the VOF simulation, Surface Evolver is employed to calculate an initial configuration consistent with experiments. Numerical instabilities at the contact line are reduced by a novel discretization of the Navier-slip boundary condition on staggered grids. The breakup of the capillary bridge cannot be characterized by a unique scaling relationship. Instead, at different stages of the breakup process different scaling exponents apply, and the structure of the bridge undergoes a qualitative change. In the final stage of breakup, the capillary bridge forms a liquid thread that breaks up consistently with the Rayleigh-Plateau instability.