The Topological Structure Design And Rheological Properties Modulation Of Dynamic Hydrogel

Dynamic chemical gel is a kind of reversible crosslinked polymer,with three dimensional network structure.The application of self-healing,shape memory,sustained release,and other functions are achieved by the dissociation and recombination of cross-links in the certain condition.This paper designed two types of gels with different topological structure.The effects of the main chain topology structure,concentration and molecular weight of main chain and macromolecular crosslinking agent,crosslinking bond strength on the modulus and relaxation time of gel and the shear thickening behavior were investigated by the linear and nonlinear rheological characterizations.The results of specific research are as follows:1.The dynamic hydrogel was formed by the main chain—the direct chain chitosan?CS?,the cross-linker—dibenzylaldehyde-functionalized poly?ethylene glycol??DF-PEG?,and the dynamic crosslink—Schiff's base.According to the characterization of linear rheological properties of the gel,the number of the elastic active chain was increased with the molecular weight and concentration of main chain or crosslinking agent.Thus,the plateau modulus and relaxation time of gel increased.The scale relationship between the plateau modulus?G₀?and the relaxation time???isG₀?25??^0.33_relax,and the relaxation process is similar with“sticky reptation”model.The relaxation behavior of the network is regulated by the junction of dissociation and association.2.The nonlinear rheological characterization of dynamic chitosan gel was investigated.The shear thickening phenomenon is caused by the transformation of inelastic active chain to elastic active chain which is induced by the non-Gaussian stretching.The number of weissenberg????5??that corresponding to the maximum shear thickening is only related to the molecular weight of the crosslinking agent and the chitosan,however,it is independent with the concentration.The degree of shear thickening is related to the density of inelastic active chain in the network.3.The dynamic chemical gel with branched PEI main chain,without entanglement,has a shorter relaxation time than the chitosan gel.The relaxation process is similar with“sticky rouse”model.The closer average distance between the crosslinking agent and the main chain,the better structure of gel with the higher modulus and the longer relaxation time.Under the condition of 1.08mol/L HCl,the stability of Schiff's base and the main chain conformation achieve the balance,thus,the gel with the best performance is obtained.The degree of shear thickening is still related to the transformation of the inelastic active chain in the network.The results in this paper represent the effects of topological structure on the relaxation and diffusion behavior.And the relationship of the molecular weight and the concentration of the crosslinking agent and the main chain,temperature,pH with modulus and relaxation time are also established.This work would be helpful to guide the design of topological structure in the field of functional hydrogels.