Regulation Of Self-assembly Behavior And Emulsification Properties Of Amphiphilic Sodium Alginate Derivatives

Natural polymers are designed and modified for food products,durg delivery and cosmetics due to their abundant sources,safety,biocompatibility,and easy degradation.The modification of natural polymers can make them more functionalized to meet its specific needs in real-world applications.In this paper,the natural sodium alginate was modified by a mild and efficient four-component condensation Ugi reaction to obtain amphiphilic sodium alginate derivatives?Ugi-Alg?with three different molecular weights.The self-assembly behavior and emulsification performance of Ugi-Alg were studied under the effects of molecular weight,electrostatic interaction and host-guest interaction.?1?Hydrophobically modified sodium alginate derivatives?Ugi-Alg?with different molecular weights were synthesized and characterized by nuclear magnetic resonance spectroscopy?¹H NMR?,¹H-¹H 2D-COSY NMR,gel permeation chromatography?GPC?and fluorescence?FM?.The self-assembly structure of Ugi-Alg in aqueous solution was studied using transmission electron microscopy?TEM?,rotational rheometer,and dynamic light scattering?DLS?.The results show that H-Ugi-Alg forms colloidal particles with compact structure and small size in aqueous solution,and low molecular weight hydrophobic sodium alginate derivatives tend to associate rather than self-assemble due to weak molecular interactions.The emulsion prepared by H-Ugi-Alg has better stability and stronger viscoelasticity.Emulsion viscoelasticity and SEM pictures show that H-Ugi-Alg not only adsorbs on the surface of oil droplets to form an elastic protective film,but also exists in the continuous phase to form a network structure to prevent the migration of droplets.The results of controlled release of curcumin from emulsion showed that the Pickering emulsion prepared by Ugi-Alg colloidal particles had a comparable controlled release effect to that of nanoparticle-stabilized Pickering emulsion.?2?The effect of ion type and strength on the self-assembly behavior and emulsification properties of high molecular weight Ugi-Alg was further explored.The effect of of Na⁺and Ca²⁺on the self-assembly behavior of H-Ugi-Alg was studied through TEM and DLS.The results show that a small amount of Ca²⁺can significantly reduce the zeta potential of H-Ugi-Alg micelles.With the increase of Ca²⁺concentration,due to the further decrease of electrostatic repulsion,H-Ugi-Alg micelles form aggregates,resulting in an increase in particle size.Ca²⁺can cross-links with the G block in the H-Ugi-Alg molecule to form a colloidal particle network structure.Na⁺can compresses the electric double layer to make H-Ugi-Alg form regular round micelles,but it cannot further reduce the zeta potential of H-Ugi-Alg micelles.The effect of Na⁺and Ca²⁺on the properties of the emulsion prepared by H-Ugi-Alg were investigated by multiple light scattering?MLS?,rheometer and scanning electron microscope?SEM?.The results show that a small amount of Ca²⁺?0.02M?can significantly improve the stability of the emulsion,as the Ca²⁺concentration further increases,the emulsion gradually becomes unstable.Due to the combination of Ca²⁺and the H-Ugi-Alg at the oil-water interface,the emulsion droplets flocculation leads to precipitation of the water phase.The interaction between Na⁺and H-Ugi-Alg is relatively weak,and the properties of the emulsion cannot be changed significantly.?3?The host-guest interaction of?-CD with the hydrophobic chain was introduced into the H-Ugi-Alg self-assembly system.The effect of?-CD host-guest interaction on the self-assembly behavior of H-Ugi-Alg was characterized by TEM,rheometer,¹H NMR.The results indicate that H-Ugi-Alg cannot self-assemble to form colloidal particles due to the hydrophobic chain participating in the host-guest interaction with?-CD,as the amount of?-CD increases,H-Ugi-Alg micelles gradually dissociated until a double-layered vesicle structure was formed.The effect of host-guest interaction on the properties of emulsion prepared by H-Ugi-Alg was characterized by rheometer and SEM.The addition of?-CD reduces the viscoelasticity of the emulsion,resulting in emulsion breaking.