No silver bullet: compositional ripening in water-in-oil emulsions*

One approach to achieve low calorie foods is to substitute regions of high calorie content with water droplets, forming water-in-oil emulsions. In complex food systems consisting of multiple species of dispersed phases, compositional ripening may occur in which the water undergoes mass transfer to regions filled with other less soluble species. 

Here we present a model system to study compositional ripening for water-in-oil Pickering emulsions. Water-in-dodecane emulsions stabilised by PMMA particles were prepared and combined with similar emulsions that included sugar in the water. Overtime the pure water droplets appear to crumple due to the loss of water; in extreme cases they eventually ‘explode’. Simultaneously, the sugar-filled droplets slowly coalesce. Evidently, our interfacial coating of particles is unable to suppress this effect. Using particle tracking, quantitative analysis of the individual droplets shows a decrease in the concentration of the sugar solution results in a reduction in the rate of change of water droplet size. Observations of droplet ‘explosions’ suggest that the driving force is vastly stronger than that of Ostwald ripening. Forthcoming experiments will further modify the system including the continuous phase and the liquid-liquid interface.