Seminar Alesia Mikhailovskaia

Surface-active agents for stabilization of all aqueous emulsions

Aqueous two-phase systems, also known as water-in-water (w/w) emulsions, represent a unique class of colloidal systems where two immiscible aqueous phases coexist. These systems arise from mixtures of hydrophilic macromolecules that are thermodynamically incompatible. Among them, the combination of dextran (Dex) and poly(ethylene glycol) (PEG) is one of the most extensively investigated, owing to its accessibility and biocompatibility. Their ability to encapsulate active compounds and control their release, while eliminating the need for organic solvents, makes such systems highly promising for applications in food science, encapsulation technologies, 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 host-guest inclusions between chemically modified Dex and PEG. 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.

Figure 1 (left) sketch of  the stabilization principle, (right) confocal laser scanning microcopy image  of  PEG-in-Dex w/w emulsion stabilized by the fluorescein-labeled interfacial complexes

[1] M. Iqbal, Y. Tao, S. Xie, et al., Biological procedures online, 2016, 18, 1.

[2] J. Esquena, Current Opinion in Food Science, 2023, 51, 101010.