A study of interactions between an air bubble and a solid surface in a liquid

Abstract

As one of the most critical steps to recover valuable particles from a slurry using flotation, knowledge of the drainage of the thin liquid film between an air bubble and a solid surface is required. The main focus of this thesis is to develop and use an integrated thin film drainage appratus (ITFDA) to investigate the physicochemical properties of the aqueous liquid film between an air bubble and a solid surface under dynamic conditions. The ITFDA was designed to measure drainage dynamics of thin liquid films confined between a solid particle, a gas bubble or/and an immiscible liquid droplet. Equipped with a bimorph force sensor, a computer-interfaced video capture device and a data acquisition system, this custom-made ITFDA allowed us to measure directly and simultaneously hydrodynamic forces, true liquid film drainage time under a well controlled external force, receding and advancing contact angles, capillary force, and detachment force between an air bubble or oil droplet and a solid, a liquid or an air bubble in an immiscible liquid. Using a diaphragm of a high frequency speaker as the drive mechanism for the air bubble or oil droplet attached to a capillary tube, this new device is capable of accurately and independently measuring forces over a wide range of hydrodynamic conditions, including bubble approach and retract velocity up to 50 mm/s and displacement range up to 1 mm. Using this device, interactions between an air bubble and a hydrophilic or hydrophobized glass sphere were measured. The results showed that the ITFDA was capable to accurately measure hydrodynamic resistance between air bubbles and solid particles in aqueous solutions, providing direct evidence of the critical roles of hydrodynamic forces and particle hydrophobicity in air bubble and particle interactions. The results from this study also showed a close relationship between bubble drive velocity, solid hydrophobicity and force barrier before three phase contact of air bubbles on hydrophobized solids in aqueous solutions. Solution pH, salt concentration and surfactant all have effects on the solid hydrophobicity, and hence change the bubble-hydrophobic solid interactions.