Behavior of Bubble Interfaces Stabilized by Particles of Different Densities

Stability of bubbles laden with particles of different densities was investigated. Capillary-held bubbles were produced and coated with particles across the density range of 1.2–3.6 g·cm–3. The materials used were poly(methyl methacrylate) (PMMA), glass, and anatase. The interaction of the bubbles, once brought into contact, was monitored using high-speed video recording. Visual inspection indicated that denser particles were more easily displaced during the contact of the bubbles and therefore the PMMA particles provided a particle barrier more resistant to coalescence. The coalescence events yielded information on the surface properties of the bubble and the detachment of particles. The attached particles commonly dampen the oscillation of the coalesced bubbles through viscous drag and change in the surface properties (e.g., area-exclusion principle). The dampening of the oscillation generally leads to a reduced mass of particles detaching from the bubble surface. It was found that the different materials investigated did not offer clear evidence of the effect of particle detachment on the bubble surface properties in the present systems. On the other hand, the detachment of different particle materials seemed to be consistent with one another when comparing the attachment and detachment forces exerted on the particles based on their density, size, and hydrophobicity. It was concluded that particles of lower density are more effective in stabilizing interfaces, and thus particle density is an important parameter in the selection of materials for the handling of dispersions.