Stability of Clay Particle-Coated Microbubbles in Alkanes against Dissolution Induced by Heating

We investigated the dissolution and morphological dynamics of air bubbles in alkanes stabilized by fluorinated colloidal clay particles when subjected to temperature changes. A model for bubble dissolution with time-dependent temperature reveals that increasing the temperature enhances the bubble dissolution rate in alkanes, opposite to the behavior in water, because of the differing trends in gas solubility. Experimental results for uncoated air bubbles in decane and hexadecane confirm this prediction. Clay-coated bubbles in decane and hexadecane are shown to be stable in air-saturated oil at constant temperature, where dissolution is driven mainly by the Laplace pressure. When the temperature increases from ambient, the particle-coated bubbles are prone to dissolution as the oil phase becomes undersaturated. The interfacial layer of particles is observed to undergo buckling and crumpling, without shedding of clay particles. Increasing the concentration of particles is shown to enhance the bubble stability by providing a higher resistance to dissolution. When subjected to complex temperature cycles, for which the effect of time-dependent temperature is dominant, the clay-coated bubbles can resist long-term dissolution in conditions under which uncoated bubbles dissolve completely. These results underpin the design of ultrastable oil foams stabilized by solid particles with improved shelf life under changing environmental conditions.