(461h) The Dynamics of Rising Oil-Coated Bubbles: Experiments and Simulations

The familiar phenomenon of gas bubbles rising in water can not only be mesmerizing to watch; it also has many important industrial applications, where the bubbles are routinely used to extract solid particles from a liquid medium. Recently, it is shown that oil-coated gas bubbles can be more effective for separating hydrophilic particles with low affinity for the air-water interface. While uncoated bubbles rising through an aqueous medium have been studied extensively, the rise dynamics of oil-coated bubbles has not yet been explored. In the present work, we report the first systematic study of the rise dynamics of bubbles engulfed in a layer of oil. Results from direct observation of the coated bubbles are compared to computer simulations and confirm a pronounced effect of the oil coat on the bubble dynamics. We consistently found that the oil-coated bubbles display a more spherical shape and straighter trajectory, yet slower rise than uncoated bubbles of comparable size. Despite the simplicity of the model we used, the simulations captured the salient qualitative features distinguishing oil-coated and uncoated bubbles. These characteristics may provide practical benefits for flotation separations with oil-coated bubbles.