Tuning The Amphiphilicity Of PH/light Responsive Host-guest Supramolecular Assemblies Of Alginate Derivatives And Its Role On The Stabilization Of Pickering Emulsions

Amphiphilic polymeric molecules can realize controllable self-assembled behavior and form a variety of self-assembled structures,which can be applied in materials science,drug delivery and cell imaging and so on.The supramolecular non-covalent host-guest interaction can effectively regulate the amphiphilicity of polymeric molecules,thus achieving the diversity and complexity of supramolecular self-assembled structures.However,the adsorption kinetics,interfacial self-assembly behavior and interfacial rheological properties of supramolecular host-guest polymers at the oil-water interface have not been thoroughly explored and studied.Therefore,this paper designs the alginate-based supramolecular host-guest polymers as a kind of structural controllability of soft colloid emulsifier to stabilize the multiple Pickering emulsion.On the basis of coupling through analysis of micro multi-scale and macroscopic properties of emulsion,it can deeply understand the interfacial stabilization mechanism of Pickering emulsions.(1)Super-amphiphilic polymers have different structural diversity and stability from small molecular super-amphiphiles.By combining the polysaccharide polymers and supramolecular host-guest chemistry,p H-responsive biopolymeric alginate chain(Alg)and photoresponsive functional group(Azo)were introduced into the supramolecular host-guest system(Alg-?-CD/Azo C12),further endowing the alginate-based supramolecular polymers with p H/light stimulus-responsiveness.Then the structural diversity of superamphiphilic polymeric self-assemblies could be realized.The structure was characterized by Fourier transform infrared spectroscopy(FT-IR)and nuclear magnetic resonance spectroscopy(~1H NMR),the photoisomerization characteristics of Azo C12 were characterized by UV-Vis spectroscopy.Molecular fluorescence spectroscopy(FM),UV-Vis spectroscopy and transmission electron microscopy(TEM)were used to characterize the structural transformation of Alg-?-CD/Azo C12 super-amphiphilic assemblies.The results showed that with the increase of p H,the balance of electrostatic repulsive force and intermolecular hydrophobic force between Alg-?-CD/Azo C12super-amphiphiles changes,and the structures of Alg-?-CD/Azo C12 super-amphiphiles changed from irregular structures,spherical structures to swollen structures.Alg-?-CD/Azo C12 super-amphiphiles can achieve reversible self-assembly and dissociation under alternate UV-Vis irradiation.Therefore,super-amphiphilic Alg-?-CD/Azo C12 assemblies can be endowed with better structural controllability upon the p H/light stimuli.(2)By using the coupling through analysis strategy of multi-scale microcosmic interfacial studies and macroscopic properties of emulsion.The effective correlation between the interfacial adsorption kinetics,interfacial rheological properties and the physical stability of the supramolecular host-guest emulsion was further investigated under the external stimulus response(p H/light).These results showed that stable Alg-?-CD/Azo C12 assembled emulsions were obtained by gently shaking for 30s at a very low amphiphilic polymeric host molecule concentration(0.1mg/m L),due to the extremely low interfacial tension of Alg-?-CD/Azo C12(0.18m N/m).Therefore,a small amount of energy input was required to provide mechanical energy to disperse the Alg-?-CD/Azo C12super-amphiphilic aggregates.Additionally,?-CD/Azo C12 supramolecular self-assemblies emulsion showed distinct phase separation,indicating that the polymeric alginate chain could endow?-CD/Azo C12 supramolecular system with more matched amphiphilicity,and benefiting the host-guest interfacial adsorption and structural stability.By combining Interfacial tensiometer(IFT),laser confocal microscope(CLSM),quartz crystal microbalance withdissipation monitoring(QCM-D)technologies,the interfacial properties of Alg-?-CD/Azo C12 supra-amphiphilic self-assemblies were measured.Scanning electron microscopy(SEM)revealed that the interfacial structures appeared inter-assembled aggregation,dissipation and slight deformation phenomenon.Additionally,the efficient relationship between the macroscopical stability of emulsions(viscosity and droplet size)and the interfacial properties were established.These results showed the interfacial tension,thickness and viscoelasticity of Alg-?-CD/Azo C12 adsorbed layer exhibited initial increase and subsequent decrease.At p H 9.12,the Alg-?-CD/Azo C12 self-assembled aggregates formed the three-dimensional network structures in the continuous phase,further avoiding the inter-droplets collision and aggregation,which benefits the stability of emulsions.Under UV light,the emulsion appears exhibited thermodynamic unstable state due to the destruction of the amphiphilicity of the interfacial films,increasing the extent of the droplets colliding and agglomerating.Therefore,the coupling through analysis of micro multi-scale and macro-emulsion properties provides a theoretical basis for the interfacial stabilization mechanism.Encapsulating kofothrin by Alg-?-CD/Azo C12 super-amphiphilic aggregates could construct the stimulus-responsive and controlled release system,technically providing a new approach for sustainable development of drug-delivery.(3)Alg-?-CD/Azo C12 super-amphiphilic polymers were used to regulate the amphiphilicity by varying the degree of interfacial aggregation,further regulating the self-assembly behavior and realizing the formation of W/O/W emulsion.The interfacial self-assembled behavior of alginate-based host-guest Alg-?-CD/Azo C12 super-amphiphilic polymers depends on the change of oil-water ratio,and then the polymeric super-amphiphilicity can be controlled.So Alg-?-CD/Azo C12 super-amphiphilic polymers with adjustable amphiphilicity can be used as a novel and efficient soft colloidal emulsifier to stabilize a variety of Pickering emulsions.When the oil-water ratio was less than 42%,it could be utilized as a typical relatively hydrophilic soft particulate emulsifier.The alginate chain(Alg)was exposed to the exterior of the polymeric super-amphiphilic assemblies,and the C12 blocks were separated into the interior of the spherical shell,which tends to stabilize the O/W Pickering emulsion.When the volume fraction of oil increased from 42%to 75%,the coverage density of internal W/O interface and external O/W interface showed highest interfacial coverage due to the low interfacial tension(2.6m N/m)of Alg-?-CD/Azo C12 super-amphiphilic polymers.Therefore,the W/O/W emulsion stabilized by Alg-?-CD/Azo C12 super-amphiphilic polymers exhibited high-efficiency stability.Subsequently,a continuous increase of oil phase(80%)resulted in a typically catastrophic phase transition.The reason may be that the stretching of the C12 chain further improves the hydrophobicity of the host-guest polymers,which tends to stabilize the W/O Pickering emulsion.In particular,the host-guest interfacial assembly-templated strategy provided an efficient route for the construction of multifunctional soft materials.Different oil/water ratios and UV light stimuli eventually lead to changes in the self-assembly behavior,further endowing the polymers with a specific amphiphilicity,and eventually form a variety of structures.Therefore,this host-guest interfacial sel-assembly-templated phase separation strategy technologically promotes the continuous development of multifunctional soft materials,which not only extends the range of traditional amphiphilic self-assembled emulsifier,but also establishs a new bridge between colloidal interface science,polysaccharide polymer and supramolecular host-guest chemistry.