Studies on the stability of thin films in bubble-particle adhesion

The critical rupture thicknesses (H_C) of thin liquid films between air bubbles and solid surfaces have been measured using an optical interferometry technique. The results of the measurements show that H_C increases with the increasing hydrophobicity of a solid and varies inversely with the work of adhesion (W_A) of water on the solid. The relationship between H_C and W_A has, therefore, been used to estimate the values of H_C for the systems in which direct measurement is not possible.

Thermodynamic calculations have been carried out for the bubble-particle adhesion process using the DLVO theory modified to include interaction energies due to structural forces. The calculations required knowledge of the values of various parameters such as, H_C, zeta potentials, and Hamaker constants for both bubbles and particles. The results of the calculations conducted on methylated silica and coal show that the thin film ruptures mainly due to the attractive structural force (i.e., hydrophobic interaction). For silica and mica immersed in dodecylamine hydrochloride solutions, the major driving force for film rupture is either the attractive electrostatic force or the hydrophobic interaction force, depending on the pH and the amine concentration.