Study On Preparation Of Gels With Different Microstructures And Their Rheological Properties

A gel is a polymer with a cross-linked three-dimensional network structure.Molecular chains are connected to each other to form a spatial network structure.A certain amount of solvent is absorbed in a solvent to swell the polymer network structure without dissolving.Because surfactant molecules have asymmetric amphiphilic structures,they can exhibit very rich phase behavior in aqueous solutions,so they can form aggregates of various structures.Therefore,we use different types of surfactant systems to build different microstructures gel.Tetradecyl dimethylamine oxide was first used as a cationic surfactant,and perfluorocarboxylic acid was used as an anionic surfactant,and compounded in an aqueous solution.The results show that the system exhibits very rich phase behavior,forming L₁micelle phase,L_αvesicle phase,precipitate phase and gel phase,respectively.The cryo-etching microscope,infrared spectroscopy,differential scanning calorimetry,small-angle X-ray diffraction,and rheology were used to further characterize the L_αphase and gel phase.The L_αphase is mainly composed of a single layer of spherical vesicles.The reason for the formation of such vesicles depends on the electrostatic interaction between anions and cations and the interaction between hydrocarbon and fluorocarbon chains.The gel phase is formed by densely packed polydisperse single-layer vesicles,and the gel has a large elastic modulus and a viscous modulus.This is determined by the rigidity of the fluorocarbon chain.The fluorocarbon surfactant chain exists in a crystalline state at room temperature,and the formation of the gel phase is caused by the co-crystallization of the fluorocarbon chain and the hydrocarbon chain.In order to examine the effect of different carbon chain lengths on the size of vesicles,gels and their rheological properties,we also studied the dodecyldimethylamine oxide and perfluoroundecanoic acid systems.The study found that the length of the hydrocarbon chain has a greater effect on the formation of the surfactant gel.As the hydrocarbon chain increases,the size of the polyhedral vesicles increases to some extent.At the same concentration of perfluoroundecanoic acid,the longer the hydrocarbon chain,the higher the viscoelasticity of the gel.The results further prove that the decisive factor for the formation of polyhedral vesicle gels is the co-crystallization of fluorocarbon and hydrocarbon chains.The paper also studies theγ-cyclodextrin/perfluorododecanoic acid surfactant system,builds a temperature-responsive hydrogel,and explores the law of its micromorphology changing with the system concentration With a view to achieving size-controllable gel construction.Studies have found that such hydrogels are temperature-responsive,that is,mixed aqueous solutions can form gels at 60°C and precipitate at room temperature.The rheological results show that the strength of the gel increases with the increase ofγ-cyclodextrin.When the molar ratio of cyclodextrin to perfluorododecanoic acid is 1:1,the viscoelasticity of the hydrogel reaches the maximum,indicating that the stoichiometric ratio of perfluorododecanoic acid and cyclodextrin is 1:1 to form a complex.The composite is a building unit of a hydrogel structure.The results of¹H nuclear magnetic resonance（NMR）tests show that the intermolecular hydrogen bonding of cyclodextrin is the main driving force for hydrogel formation.