Pickering Double Emulsions Stabilized by a Binary Mixture of Anionic and Cationic Polysaccharide Nanocrystals

Pickering double emulsions have attracted increasing interest due to their potential applications in food, pharmaceuticals, and cosmetics. Currently, the preparation of Pickering double emulsions relies heavily on surface treatments of particle stabilizers, particularly in the one-step emulsification approach. This strategy is inconvenient and may result in limitations that hinder practical applications. Here, we demonstrate that oppositely charged starch nanocrystals and chitin nanocrystals can be used simultaneously to form Pickering double emulsions by using a one-step emulsification procedure that is independent of surface modifications. Starch nanocrystals and chitin nanocrystals exhibit a synergistic effect in stabilizing both the internal and the external droplets. Using both natural nanocrystals together produces Pickering double emulsions with improved stability, which is attributed to the adsorption of binary colloid complexes formed by the two nanocrystals at the oil/water interface of opposing curvatures. The electrostatic interactions between the nanocrystals drive the formation of binary colloid complexes. The starch/chitin mass ratio, aqueous pH, and salt concentration all influence the hydrodynamic size, ζ-potential, and surface wettability of the resulting complexes prior to emulsification, which collectively govern double emulsion formation and stability. As an illustration, the prepared Pickering double emulsion effectively protects the lipophilic β-carotene and hydrophilic riboflavin sodium phosphate simultaneously under different conditions.