Combining hydrodynamics and molecular kinetics to predict dewetting between a small bubble and a solid surface.
This paper examined the dewetting between a small air bubble and a solid surface in deionised water. Hydrodynamics was used in conjunction with surface molecular kinetics to model and predict the velocity of the moving contact line as a function of the dynamic macroscopic contact angle. The dewetting hydrodynamics was modelled following the approach developed specifically for drops and bubbles using the (absolute) coordinate system with the origin located at the centre of the contact area, which does not move with the moving contact line. The model provides accurate corrections unavailable in the generic hydrodynamic theories developed by Voinov and Cox, and removes the need for a macroscopic length scale employed in their generic theories. Molecular kinetics was used to determine the contact angle of the inner region close to the contact line, where the hydrodynamic approach breaks down due to the singularity. Unlike the generic hydrodynamic theories, the inner (microscopic) angle in our combined model is not a constant (a fitting parameter) but is a function of the moving contact line velocity and other molecular properties of the interfaces. The combined model agreed with the experimental data and produced physically consistent values for the slip length, molecular jumping distance and frequency. The dissolved gases accumulated at the non-wetting solid-liquid interface may influence the slip length.