Construction,Regulation And Application Of Emulsion System Stabilized By TiO₂ Nanoparticles

The traditional emulsions stabilized by surfactants are thermodynamically unstable,which commonly require higher emulsifier concentration than critical micelle concentration（CMC）to ensure kinetic stability.Pickering emulsions stabilized by surface-active solid particles exhibit superior stability owing to the formation of dense particles adsorbed at the oil-water interface,which prevent droplets from coalescence.In recent years,the novel emulsions stabilized by similarly charged surfactants and solid particles have been widely studied,in which surfactants disperse at the phase interface while solid particles exist in the continuous phase.Ti O₂ nanoparticles have become a common emulsifier due to their excellent UV shielding ability,environmental friendliness,high stability,good biocompatibility and easy surface modification,and are widely used in food,personal care products,photocatalysis and other fields.However,flexible and controllable stability is usually needed for emulsion system in some fields,such as encapsulation,transportation and interfacial catalysis.The stimuli-responsive emulsions have attracted wide attention.Therefore,in this paper,the redox and p H responsive emulsions stabilized by synthetic surfactant ferrocene azine（Fc⁺A）and Ti O₂ nanoparticles were studied.Subsequently,proanthocyanidins（OPC）and red cabbage anthocyanins（RCA）were introduced respectively to construct emulsions together with Ti O₂ nanoparticles.The factors affecting stability,the stabilization and responsive trigger mechanism of the three emulsion systems,and their applications in the field of sunscreen and intelligent packaging were explored.The specific research results are as follows:1.The redox and p H dual responsive emulsions stabilized with Ti O₂ nanoparticles and ferrocene fluorescent surfactant Fc⁺A with redox-active were prepared.It was found that the majority of Fc⁺A adsorbed at the oil-water interface alone to reduce the interfacial tension,and the minority of Fc⁺A adsorbed onto the surface of Ti O₂ nanoparticles via electrostatic attraction,reducing the hydrophilicity of the particles to disperse at the oil-water interface in the form of Fc⁺A and Ti O₂ complex,which hindered the aggregation of droplets.The proposed synergistic stabilization interaction between surfactants and surfactant-modified nanoparticles provided a new understanding for the stabilization mechanism of emulsions.Moreover,the stimuli responsiveness was attributed to the reversible adsorption of surfactants on nanoparticle surfaces controlled by p H and redox as well as the change in amphiphilicity of surfactants controlled by redox.The novel dual-responsive system provided a simple and feasible method for the intelligent regulation of emulsions.2.A novel O/W emulsion was stabilized by Ti O₂ nanoparticles in combination with OPC with antioxidant and UVB shielding activity.After wrapping the UVA filter avobenzone（AVB）in the oil phase（No.26 cosmetic grade white oil）,the emulsion was endowed with the ability to resist UVB and UVA.The results showed that the droplet size decreased with the increase of OPC concentration,but the increase of the content of Ti O₂ nanoparticles had little effect on the droplet size.This could be attributed to the fact that OPC aggregated at the oil-water interface,reducing interfacial tension,while Ti O₂ nanoparticles were dispersed in the continuous water phase,hindering droplet coalescence.In addition,the emulsion showed excellent free radical scavenging ability for·OH and·O₂^-,indicating the good antioxidant activity.This method of organically combining UVB,UVA filters and antioxidant active agents with emulsion as a carrier provided a new idea for the preparation of full-band sunscreen emulsions.3.The W/O Pickering emulsion was prepared by encapsulating the color indicator RCA in the inner phase with hydrophobic Ti O₂ nanoparticles modified by silane coupling agent as lipophilic emulsifier.The emulsion was coated on a polyvinylidene fluoride（PVDF）substrate to develop an indicator film for salmon meat freshenss monitoring.The ability of UV resistance and preventing anthocyanin from dissolving out at high humidity were endowed by Ti O₂ nanoparticles and the adsorption of W/O Pickering emulsion on PVDF substrate,respectively.Moreover,the as-prepared film also presented good selectivity and broad linear range towards gaseous amines such as trimethylamine and was used to monitor freshness of salmon meat at 4℃from 0 to 7 days.The color changes of the film were highly positively correlated with the content of TVB-N in meat samples.This indicator film based on W/O Pickering emulsion might provide some new ideas for sensors development with hydrophobicity and UV-proof in areas of intelligent packaging.