Self-Assembly And Emulsification Properties Of Photo-Responsive Amphiphilic Alginate Derivatives In Aqueous Solution

Alginate is a natural water-soluble polymer which is abundantly present in the cell walls of algae plants.It is an excellent natural food additive with good biocompatibility and unique physical and chemical properties,which has been widely used in the food,cosmetics and pharmaceutical industries.In this paper,sodium alginate was used as raw material to obtain a series of photo-responsive alginate derivatives via Ugi reaction,which endued the alginate with optical activity and retaining its original properties at the same time.The emulsifying properties of photosensitive alginate derivatives and the effects of UV on their emulsifying properties were investigated.Firstly,a photosensitive amphiphilic sodium alginate(SA-Stilbene)containing a stilbene unit was synthesized by Ugi reaction.The data of Fourier transform infrared spectroscopy(FTIR)and 1H-NMR indicates successful synthesis.The critical aggregation concentration was 0.016 g/1 which is determined by fluorescence spectroscopy.The UV-Vis-NIR spectrophotometer was used to characterize the light-responsive properties and reversibility of SA-Stilbene.The self-assembly of SA-Stilbene in aqueous solution dissociated due to hydrophilicity after UV irradiation through the TEM images.Based on the change of amphiphilicity,the effect of UV light on the emulsifying properties of SA-Stilbene was studied.The optical microscope showed that the droplet size of the emulsion after light treatment increased from 20?m to 40?m,and oil phase aggregation phenomenon appeared.The stability of the emulsion before and after UV illumination was evaluated by multiple light scattering and DHR rheometer.The results show that UV reduces the emulsion stability by enhancing the hydrophilicity of the interface film.To broaden the application of alginate derivates on Pickering emulsion,we modified the surface of Nano-silica and obtained aldehyde-capped silica(SiO2-CHO).Polymer-modified silica(SA-Stilbene@SiO2)was synthesized via Ugi reaction with SA,DSD acid and cyclohexyl isocyanide.The structure was characterized by FTIR and XPS.The data of thermogravimetric analysis(TGA)show that the degree of substitution of SA-Stilbene@SiO2 was 17.95%.The particle dispersion was improved to some extent after modifying.SA-Stilbene@SiO2 particles were confirmed to be amphiphilic by emulsification experiments;in addition,UV-Vis-NIR spectroscopy indicated that it also had reversible light-responsive properties,and it was confirmed by multiple light scattering instruments that the stability of the emulsion can be regulated by the UV illumination time.At last,we prepared a photo-sensitive amphiphilic alginate derivative(SA-AMC)base on photodimerization via Ugi reaction.The self-assembly of SA-AMC in aqueous solution was observed to be more compact after UV through the image of TEM,which results a smaller particle of emulsion.It was confirmed by SEM electron microscopy that the emulsion is a Pickering emulsion stabilized by a soft particle that formed by self-assembly of SA-AMC in aqueous solution,and UV light could reduce the adsorption of colloidal particles at the oil-water interface.It has been demonstrated by multiple light scattering instruments and DHR rheometers that UV light can increase the rigidity of the interface of the Pickering emulsion and improve the stability of the emulsion.This has important guiding significance for improving the long-term storage performance of Pickering and enhancing its interface rigidity.