Amphiphile-like stabilizers for water-in-water emulsions

Aqueous two-phase systems or water-in-water (w/w) emulsions constitute a distinct type of colloidal systems in which two immiscible aqueous phases coexist. They are formed from mixtures of hydrophilic macromolecules that are thermodynamically incompatible such as dextran (Dex) and poly(ethylene glycol) (PEG). The capacity to encapsulate active ingredients and regulate substance release, while being composed of fully biocompatible components, holds great potential for application of such systems in food science, encapsulation and drug delivery [1]. However, the stabilization of these peculiar emulsions is much more challenging than for common ones because the interface is not only absent of distinct hydrophobic and hydrophilic regions but is also thicker than that of oil-water systems [2].We stabilize such w/w emulsions with macromolecular complexes that have affinity for both PEG- and Dex-phases, and therefore, are located at the droplet surface similar to ordinary surfactants at water/oil interfaces. The stabilizing complexes are formed due to 2 :1 inclusions of curcubit[8]uril (CB[8]) with PEG and Dex functionalized with methylviologen (MV) and naphthol (Np), respectively. By finely adjusting the size of the polymers and the grafting ratio with the host groups, we aim at controlling the adsorption kinetics and the strength of the polymer interactions at the interface. This approach enables a systematic investigation of interfacial host-guest complexation as a means of stabilizing w/w emulsions.