Influence of hydrophobic particles on the film drainage during bubble-solid interaction

In this article, we investigate the complex drainage behavior of liquid ("dimple") films entrapped between hydrophilic glass substrates and air bubbles in water and aqueous suspensions of polystyrene (PS) particles. The film drainage was monitored by capturing the evolution of spatial-temporal thicknesses using interferometry. Faster drainage of the entrapped film is observed in the PS colloid suspensions compared to the water. The film drainage strongly depends on the interface boundary conditions. Our experiments reveal that the air-liquid interface of the entrapped film becomes partially mobile in the PS suspensions, which results in faster drainage. The hydrophobic PS particles tend to migrate toward the air-water interface and form an ordered layer. We argue that the adsorbed layer of PS particles makes the bubble surface elastic, delaying the formation of the immobile interface.