Study of particle-bubble interaction using atomic force microscopy: current possibilities and challenges

Study of interaction forces between mineral particles and air bubbles is a key to understanding flotation processes. Measurement of such interaction forces has only recently been made possible with the introduction of the atomic force microscope (AFM) and the colloidal probe technique. Using AFM, interactions between a single particle attached to the AFM cantilever and an air bubble placed on a flat hydrophobic surface are measured in an aqueous environment. Interaction forces prior to rupture of the interfacial water film as a function of the hydrophobic surface state can be established, as shown in the present study. Additionally, the effect of the hydrodynamic force between approaching air bubble and particle is quantified. Despite the great potential of the AFM colloidal probe technique for studying particle - bubble interactions, several challenges pertaining to the AFM design, experimental procedure, and data analysis have to be addressed due to deformation of the air-water interface. For example, such issues as the range of the piezoelectric translator and cantilever deflection, determination of the bubble spring constant, and identification of the point of contact between bubble and particle are now under consideration.