Bubbles nucleation in supersaturated emulsion drops.

Bubble nucleation plays a significant role in applications ranging from food and beverages to cosmetics, polymer foams, and advanced porous materials. While extensively studied in homogeneous solutions and particle suspensions, bubble nucleation mechanisms in heterophasic liquid dispersion, such as emulsions, are less understood. This study hypothesizes that tuning physicochemical and mixing hydrodynamics allows design over the bubble nucleation and growth under mild gas supersaturations. Supersaturated oils were emulsified under mild stirring, followed by rapid decompression to trigger nucleation. The process was analyzed by monitoring changes in emulsion volume and optical microscope observations. Key parameters such as gas saturation pressure, viscosities of the continuous and dispersed phases, gas solubility and dissolution kinetics, and mixing intensity were systematically varied. Bubble nucleation occurs mainly via a heterogeneous mechanism, accelerated by shear and gas migration kinetics. Increased oil phase viscosity enhanced bubble formation and retention in droplets, while higher aqueous phase viscosity suppressed nucleation in the continuous phase. The number and size of the obtained bubbles varied significantly, depending on the phase of nucleation origin and the physicochemical conditions. This study reveals pathways to optimize bubble nucleation and initial growth dynamics, which can be used for optimization of pore size distribution of emulsion-based materials.