The Synergy Of Ugi-Alg/SiO₂ And Its Effect On The Stability And Rheological Properties Of Pickering Emulsions

Natural polymer surfactants are widely used in the fields of food,medicine and cosmetics due to their biocompatibility,low cost,availability,and easy degradation.In this paper,the natural macromolecule sodium alginate was modified by a mild and efficient chemical reaction to obtain sodium alginate derivatives with different molecular weights.Stability of the suspension system of sodium alginate dispersed SiO2 was determined.And the adsorption behavior at the liquid interface was explored.At the same time,the effect of the macromolecular particle emulsifier formed by the polymer and the solid particles on the properties of the emulsion was investigated.Amphiphilic sodium alginate derivatives were synthesized by Ugi four-component condensation reaction.The suspension system with different stability was obtained by adsorption of different molecular weight Ugi-Alg on the surface of SiO2 particles.The data of fourier transform infrared spectroscopy(FTIR),1H nuclear magnetic resonance spectroscopy(1H NMR)and fluorescence(FM)indicate that the three derivatives were synthesized successfully.The stability of the suspension system dispersed by Ugi-Alg and the adsorption characteristics of the polymer on the surface of the particles were characterized by dynamic light scattering(DLS),multiple light scattering(MLS),turbidimeter,total organic carbon analyzer(TOC),and transmission electron microscopy(TEM).The results show that the high molecular weight Ugi-Alg(H-Ugi-Alg)has stronger hydrogen bonds with SiO2,which can make Ugi-Alg to closely adsorped on the surface of particles,and the concentration near the CAC value makes the suspension have better dispersion stability.And the stability of the system is promoted by the electrostatic steric hindrance.Secondly,the synergy of Ugi-Alg and SiO2 on the properties of Pickering emulsions was further investigated.The effects of particle concentration,Ugi-Alg molecular weight and pH on O/W emulsion synergistic stabilized by Ugi-Alg/SiO2 was investigated by some methods such as MLS,optical microscopy(OM),laser confocal microscopy(DLSM)and DHR rheometer.The effects of stability and rheology of these Pickering emulsions,as well as possible stabilizing mechanisms have also been described.The results show that there is a synergistic effect between the Ugi-Alg and SiO2.The H-Ugi-Alg system with a particle concentration of 2 wt%has the highest stability and viscoelasticity,and the stability and viscoelasticity of Pickering emulsion stabilized by H-Ugi-Alg/SiO2 at a pH of 3.44 is the top one.Therefore,the stability of Pickering emulsion can be adjusted by controlling particle concentration,Ugi-Alg molecular weight and pH.The strong interaction between H-Ugi-Alg and SiO2 and the bridging effect of Ugi-Alg can improve the rigidity of the three-dimensional network structure of emulsion.The pH can adjust the charge on the surface of the particles and it can promote the flocculation of the particles to further improve the the stability of the emulsion.Finally,?-CD grafted onto sodium alginate using the Ugi reaction were obtained another sodium alginate derivative,and there is a specifically identified with the hydrophilic modified azobenzene derivative(Azo-PEG).As a result,a supramolecular polymer is formed.Pickering emulsion was stabilized by Ugi-Alg-CD/SiO2 particle emulsifier to prepare a dual-responsiveness emulsion with light and pH response.The structural composition of the host molecule(Alg-CD)was verified and characterized by FTIR,1H NMR and FM,and the photoresponse of the guest molecule(Azo-PEG)was investigated by 1H NMR,UV-Vis and fluorescence spectra(FM).The effects of ultraviolet light and pH on the stability of emulsions formed by super-amphiphilic-molecules were investigated.It opens up new ideas for the application of emulsions stabilized by light and pH-responsive sodium alginate systems.