Synthesis of sinapic acid modified sodium hyaluronate particles and the one-step processing of multiple Pickering emulsion

Abstract

In this study, a series of sodium hyaluronate (HA) polymer molecules grafted with different amounts of sinapic acid (SA) groups were synthesized by adjusting the esterification reaction time, and the introduction of SA endows the polymer with both amphipathy and UV absorbability. The amphipathic polymer molecules (HA-SA) tend to self-assemble into polydisperse colloid particles and the particle properties of HA-SA, such as particle size, zeta potential as well as the interfacial activity were studied in detail. The results indicate that the properties of HA-SA particles prepared with different esterification reaction time are quite different due to the different graft amounts of SA. The graft amount of SA increased with the prolongation of esterification reaction time, and the interfacial activity of the obtained HA-SA particles also increased gradually, but an excessively high graft amount would make the polymer too hydrophobic and thus lead to the interfacial activity reduce slightly. By controlling the esterification reaction time within an appropriate range, the prepared particles show significant interfacial activity and are apt to linger on the interface of oil-water to reduce the interfacial tension, which has potential to be a new promising stabilizer of emulsions. Further studies show that, benefiting from the polydispersity of the HA-SA particles, the water-in-oil-in-water (W/O/W) multiple Pickering emulsion can be prepared by one-step homogenization using HA-SA particles as stabilizer. Different from the inorganic particle emulsifiers and their stabilized Pickering emulsions, the particles that self-assembled by HA-SA amphiphilic polymers and their stabilized Pickering emulsions have obvious sensitivity to pH and temperature due to the existence of both COO- and OH- in HA molecule, which provides a new strategy for developing stimulus-responsive Pickering emulsifiers. The excellent moisture retention of HA and the protection of SA against UV radiation make HA-SA particles potentially a high-end cosmetic emulsifier accompanied with moisturizing and sunscreen effects on skin.