Thinking outside the box: Placing hydrophilic particles in an oil phase for the formation and stabilization of Pickering emulsions

Pickering emulsions, also known as particle stabilized emulsions, are one kind of extremely important emulsion for both fundamental research and practical applications. Many colloidal particles have been utilized as emulsifiers to stabilize Pickering emulsions. However, the most challenging issue is preparing Pickering emulsions with highly hydrophilic particles, because their adsorption onto oil-water interfaces is either thermodynamically or kinetically unfavorable. Although several strategies have been developed to overcome the poor ability of the hydrophilic particles to stabilize the emulsions, surface modification and functionalization of the hydrophilic particles or a change in solvent (i.e. water phase) conditions such as pH and ionic strength is required. Herein, we present an effective and not yet explored strategy to stabilize Pickering emulsions with unmodified highly hydrophilic particles, strikingly, without changing the solvent conditions. The innovative aspect of the strategy presented here is the unconventional dispersion of hydrophilic particles in an oil phase before emulsification, while the results experimentally demonstrate the theoretical calculations predicted more than a decade ago. This study will promote the diversity of Pickering emulsions and expand their real-world applications.