Coupled Hydrodynamic and Surfactant Effects on Liquid Film Drainage Dynamics between Bubble and the Solid Surface

Processes such as flotation and multiphase chemical reactions are typically carried out in turbulent aqueous environments, however, the coupling mechanism between the solution environment and turbulence during bubble-particle attachment remains unclear. This study systematically investigates the thinning dynamics of liquid films between bubbles and solids in flow systems using high-speed microinterferometry. Results indicate that an increase in interfacial approach velocity significantly affects liquid film formation and drainage by enhancing hydrodynamic effects. This leading to pronounced thickness differences between the film center and rim, along with concave deformation, that increases the retained liquid volume. Simultaneously, however, the steeper center-rim pressure gradient effectively speeds up drainage. Conversely, raising surfactant concentration markedly suppresses drainage: at high concentrations, the overall film thickness and deformation increase, thinning slows, and drainage time extends by more than an order of magnitude. This behavior is due to surfactant adsorption, which changes the interface toward an immobile state, increases viscous resistance, reduces bubble internal pressure, and maintains a higher equilibrium film thickness. Furthermore, investigations on hydrophilic surfaces confirm that the above conclusions can be extended to hydrophilic systems. Kinetic analysis further uncovers a coupled effect between interfacial approach velocity and surfactant adsorption: high-speed flow can cause nonuniform adsorption layers on the bubble interface, partly restoring local interfacial mobility and thereby weakening the inhibitory effect of surfactants on drainage. These findings clarify the individual and combined roles of hydrodynamics and surfactant adsorption in liquid film thinning, offering valuable theoretical insights for optimizing mineralization processes and enhancing bubble-solid attachment efficiency.