Dynamic aspects of small bubble and hydrophilic solid encounters

The capture of solid particles suspended in aqueous solution by rising gas bubbles involves hydrodynamic and physicochemical processes that are central to colloid science. Of the collision, attachment and aggregate stability aspects to the bubble-particle interaction, the crucial attachment process is least understood. This is especially true of hydrophilic solids. We review the current literature regarding each component of the bubble-particle attachment process, from the free-rise of a small, clean single bubble, to the collision, film drainage and interactions which dominate the attachment rate. There is a particular focus on recent studies which employ single, very small bubbles as analysis probes, enabling the dynamic bubble–hydrophilic particle interaction to be investigated, avoiding complications which arise from fluid inertia, deformation of the liquid–vapour interface and the possibility of surfactant contamination.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Focus on very small, 20-120 µm diameter bubble-hydrophilic solid encounters. ► New approaches for measuring dynamic bubble-solid interaction forces. ► Interactions over the force range of natural colloid interactions with negligible bubble deformation and inertia are reviewed.