Stabilization mechanism of double emulsions made by microfluidics

Abstract

The stability of double emulsions is crucial for their application as delivery systems and microcapsule templates. However, this stability is often challenged by many molecular species present in customized formulations and by the fast dynamics when microfluidic emulsification processes are used. With the help of designed single emulsion experiments, particle contact angle measurements and interfacial rheology, we investigate the stabilization mechanisms of typical double emulsion formulations containing colloidal particles in the middle oil phase and surfactants in the continuous aqueous phase. In contrast to the inefficient stabilization with conventional surfactants, we find that colloidal particles and surface active polymers are able to quickly form a strong elastic film at the oil–water interface that prevents rupture of the thin fluid separating adjacent droplets, thus providing an efficient means to stabilize double emulsions within the short timescales of microfluidic processes.