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

Abstract

In order to characterize very weakly adhesive surfaces, we have developed a quantitative test inspired by the JKR 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 which depends on the fluid viscosity, a dynamic regime is observed, characterized by the formation of a flat pancake of fluid on the coating which 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 slightly different perfluorinated coatings.3

Zipping Effect on Omniphobic Surfaces for Controlled Deposition of Minute Amounts of Fluid or Colloids

“…From the study of millimeter‐sized capillary bridges, Vagharchakian et al compared the deposit volume to the liquid bridge stretching velocity 19. They pointed out that the larger this stretching velocity is, the larger the remaining volume is after bridge failure.…”

The shape of two-dimensional liquid bridges

“…If the film is not infinitesimally thin, what we have instead is a liquid bridge or capillary bridge. Liquid bridges are relevant in many contexts, such as sand art [2]; atomic-force microscopy in high-humidity environments [3]; soldering [4]; the testing of weakly-adhesive solid surfaces [5]; in lungs, where they may close small airways and impair gas exchange [6]; the wet adhesion of insects and tree frogs [7]; the feeding of shore birds [8]; the spontaneous filling of porous materials [9]; or as tools for contact angle measurements [10]. Liquid bridges may cause attraction or repulsion between the bodies they connect, which may be surfaces (flat or curved), particles, or other liquids [11].…”

Statics and dynamics of capillary bridges

“…With the development of patterning and lithography studies of capillary bridges in slit pore geometry became important [3]. Further implementation of CB can be found in the so-called weakly adhesive solid surfaces studies [4].…”