Abstract
We present contactless atomic-force microscopy measurements of the hydrodynamic interactions between a rigid sphere and an air bubble in water at the micro-scale. The size of the bubble is found to have a significant effect on the response due to the long-range capillary deformation of the air-water interface. To rationalize the experimental data, we develop a viscocapillary lubrication model accounting for the finite-size effect. The comparison between experiments and theory allows us to measure the air-water surface tension, without contact, paving the way towards robust contactless tensiometry of polluted air-water interfaces.
Highlights
We present contactless atomic force microscopy measurements of the hydrodynamic interactions between an oscillating sphere and a bubble in water at the microscale
The interfacial rheology is usually measured with the Langmuir trough [10,11,12], oscillating-disk devices [13,14], particle tracking techniques [15,16,17,18], oscillating pendant drop [19,20,21,22], or through the measurement of capillary waves [23,24,25,26,27]
From the measurement of the hydrodynamic force, we have shown in particular that the viscous component of the force contains a signature of the advection of impurities adsorbed at the interface
Summary
We present contactless atomic force microscopy measurements of the hydrodynamic interactions between an oscillating sphere and a bubble in water at the microscale. The size of the bubble is found to have a significant effect on the response due to the long-range capillary deformation of the air-water interface. The atomic force microscope (AFM) is another powerful tool to probe capillary phenomena such as the interaction between bubbles [28,29] or droplets [30,31,32], as well as dynamical wetting [33,34,35,36,37,38] and the boundary conditions of flows at a water-air interface [39,40,41].
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