Capillary Bridge Formation and Breakage: A Test to Characterize Antiadhesive Surfaces

TL;DR

This paper introduces a quantitative test based on capillary bridge dynamics to characterize very weak adhesive surfaces, analyzing shape, kinetics, and regimes of bridge rupture across various coatings and liquids.

Contribution

The study develops a novel test method inspired by JKR adhesion testing, specifically for very weakly adhesive surfaces, incorporating dynamic and quasi-static regimes analysis.

Findings

Different rupture regimes identified, including quasi-static and dynamic.

The volume of residual drops depends on the dynamical regime and coating differences.

The test effectively distinguishes between weakly adhesive coatings, demonstrated with perfluorinated surfaces.

Abstract

In order to characterize very weak adhesive surfaces, we have developed a quantitative test inspired by the Johnson, Kendall, and Roberts adhesion test for soft adhesives, which relies on the formation and then the rupture of a capillary bridge between the surface to be tested and a liquid bath. Both the shape and the kinetics of breakage of the capillary bridge for various coatings put into contact with liquids of various viscosities and surface tensions have been studied. Several pull off regimes can be distinguished. For low pull off velocities, a quasi-static regime is observed, well described by capillary equations and sensitive to the hysteresis of the contact angle of the fluid on the coating. Above a critical pull off velocity that depends on the fluid viscosity, a dynamic regime is observed, characterized by the formation of a flat pancake of fluid on the coating that recedes more slowly than the capillary bridge itself. After the breakage of the capillary bridge, a small drop can remain attached to the surface. The volume of this drop depends on the dynamical regime and is strongly affected by very small differences between the coatings. The aptitude of this test in characterizing very weakly adhesive surfaces is exemplified by a comparison between three different perfluorinated coatings.