Adhesion of a particle to a liquid / bubble interface is an important phenomenon experienced in many processes, including gas-slurry reactions and wastewater flotation processes. Particle adhesion depends upon the surface properties of the bubble and particle and upon the fluid mechanics of the system. The probability of particle attachment to a bubble surface is governed by several sub-processes. For adhesion to occur, a particle must be intercepted by the bubble, the particle must adhere to the bubble surface, and a stable three-phase contact must be formed. The important subprocesses are difficult to directly observe due to the very small length and time scales involved.

My research has developed experimental methods to study the three-phase interactions found in particle to bubble adhesion. High-speed, high-magnification imaging allows direct observation of the interaction between a particle and a bubble in many different system chemistries. Visualization and imaging analysis methods for the study of particle adhesion to stationary bubbles and bubbles in a flow field will be presented. The systems allow quantification of the effect of system surfactant, particle size, bubble size and nature of the particles on particle to bubble attachment and examination of the adhesion stability.

Our work has focused on the flotation of ink particles for removal from paper recycling streams. Qualitative observations, in the form of still images and digital movies, have allowed examination of the extent of particle to bubble adhesion. The role of surfactants, Calcium ions, and particle size in the flotation of toner inks in deinking flotation systems has been quantified. High-speed imaging has also been used to directly observe the mechanisms of particle collision, adhesion, and stability for model particles.