Interaction force between an air bubble and a hydrophilic spherical particle in water, measured by the colloid probe technique

Colloid Probe Atomic Force Microscopy (CP AFM) technique has been used to measure the force of interaction between a hydrophilic silica sphere and an air bubble in water and symmetrical electrolyte solution. Since all the measurements were carried out above the isoelectric point of silica, it was found that, as predicted by classical DLVO theory, no attractive force was observed. Repulsive force measured in-between the colloid probe and the air bubble was found to be dependent strongly on ionic strength of the solution (i.e. electrolyte concentration) and decayed with increase in separation. To exclude any effect of hydrodynamic force, and therefore work within the regime where surface forces are of significant importance, all the measurements were carried out at low piezo scan velocity (not greater than 0.5 µm s− 1). The results we have obtained contribute to elucidate controversial experimental data reported in the literature on the interaction force acting among such interfaces.