Impact of interface approach velocity on bubble coalescence

We studied the coalescence of air bubbles in pure water and aqueous solutions of inorganic electrolytes and frothers by measuring the lifetimes of thin free aqueous films formed at a broad range of interface approach velocities with using a microfabricated film holder. For pure water, at ultra-low approach velocities the formed films were highly unstable, and the film lifetimes increased with increasing the approach speed, reaching a peak before decreasing at higher approach speeds. Similar trend was observed for the lifetimes of the films containing inorganic electrolytes and frothers of different types and concentrations. The results suggested that interface approach velocity might be an important factor affecting bubble coalescence in flotation.

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► Interface approach velocity has a pronounced impact on bubble coalescence.
► Foam film stability reaches a maximum at an intermediate approach speed.
► Pure water films formed at ultra-low interface approach velocities are highly unstable.