Visco-elastic drag forces and crossover from no-slip to slip boundary conditions for flow near air-water interfaces

Abstract

The "free" water surface is generally prone to contamination with surface impurities be they surfactants, particles or other surface active agents. The presence of such impurities can modify flow boundary near such interfaces in a drastic manner. Here we show that vibrating a small sphere mounted on an AFM cantilever near a gas bubble immersed in water, is an excellent probe of surface contamination. Both viscous and elastic forces are exerted by an air-water interface on the vibrating sphere even when very low doses of contaminants are present. The viscous drag forces show a cross-over from no-slip to slip boundary conditions while the elastic forces show a nontrivial variation as the vibration frequency changes. We provide a simple model to rationalize these results and propose a simple way of evaluating the concentration of such surface impurities.

11 pages, 5 figures

Cited by in corpus (13)

• Microscale Marangoni Surfers
• A single parameter can predict surfactant impairment of superhydrophobic drag reduction
• Azimuthal instability of the radial thermocapillary flow around a hot bead trapped at the water-air interface
• Contactless rheology of finite-size air-water interfaces
• The acoustic radiation force on a spherical thermoviscous particle in a thermoviscous fluid including scattering and microstreaming
• Capillary nanowaves on surfactant-laden liquid films with surface viscosity and elasticity
• Hydrodynamic response of a surfactant-laden interface to a radial flow
• Near-field probe of thermal capillary fluctuations of a hemispherical bubble
• On the shear-driven surfactant layer instability
• Apparent line tension induced by surface-active impurities
• Surfactant-driven instability of a divergent flow
• Slug bubble growth and dissolution by solute exchange
• Microparticle Brownian Motion near an Air-Water Interface Governed by Direction-Dependent Boundary Conditions