Drag force on a spherical particle moving through a foam: The role of wettability

Experimental measurements are presented of the drag force on a spherical probe particle moving through an aqueous foam at the low speed limit, for particle/bubble radius ratios of 1.5–3.0. In froth flotation, this force is critical for understanding selectivity of these particles. The effect of surface wettability and particle diameter is both explored. A ‘hybrid’ model of the force is developed and compared with the experimental data. This combines forces due to yield of the foam ‘continuum’, both in the bulk and at the foam–particle interface, with forces due to attachment/detachment of individual foam nodes from the particle.