Preparation And Investigation Of Shape Memory,Self-healing Hydrogels

Smart hydrogel has great practical value and application prospect in practical application.At present,there are few studies on hydrogels with both self-healing and shape memory ability.The coordination effect between dopamine and Fe³⁺ is widely found in nature and has high association constant and reversibility,which can endow polymers with novel properties,such as multiple stimulus responsiveness,self-healing and shape memory property and so on.In this paper,the 4 arm PEG-Dopa-Fe³⁺ hydrogel with double cross-linked network was formed by the coordination and oxidation reactions between dopamine and Fe³⁺.Moreover,the c-4 arm PEG-Dopa hydrogel was prepared by oxidation of 4 arm PEG-Dopa.In the second chapter,4 arm PEG-Dopa-Fe³⁺ hydrogel was prepared by substitution reaction,hydrolysis reaction and amide coupling reaction.The chemical structure of 4 arm PEG-Dopa was confirmed by FT-IR and 1H-NMR.The UV-vis and Raman spectra were done to demonstrate the coordination and oxidation of 4 arm PEG-Dopa and Fe³⁺.The rheological properties and mechanical properties of the hydrogel were investigated by rheometer and universal material mechanical testing machine.The results indicated that the hydrogel possessed great mechanical properties and its mechanical properties were affected by pH and Fe³⁺.The higher the content of Fe³⁺,the stronger mechanical hardness of gel but the worse the elongation.The hydrogel had the best mechanical properties when the pH was 9.In the third chapter,the ratio of physical cross-linking and chemical cross-linking in the gel was controled by adjusting the content of Fe³⁺.The self-healing function of the gel was analyzed by rheological and tensile tests,and the shape memory ability of hydrogel was investigated by changing the content of Fe3 + The results indicated that the hydrogel had great self-healing ability,and the self-healing ability became weaker with the increasing content of Fe³⁺.The hydrogel possessed great shape memory ability by pH stimulation.The hydrogel with a Dopa:Fe³⁺ molar ratio of 1:0.8 had excellent self-healing performance,shape memory performance and great mechanical properties.In the fourth chapter,the c-4 arm PEG-Dopa hydrogel was prepared by the oxidation reaction between 4 arm PEG-Dopa and sodium periodate?NaIO4?,UV-vis was done to demonstrate the chemical structure of the c-4 arm PEG-Dopa.The crystallinity,thermal properties and shape memory properties of the c-4 arm PEG-Dopa were analyzed by X-ray diffraction?XRD?,differential scanning calorimetry?DSC?and dynamic mechanical analysis?DMA?.The results showed that the c-4 arm PEG-Dopa hydrogel had excellent tensile strength,and the polymer material possessed great shape memory properties.The infiltration of a small amount of water molecules can dissolve the crystal region in hydrophilic PEG,which resulted in decreasing of the crystallinity and the melting point of the polymer,but the shape memory performance of the material were not influenced significantly.The shape fixation rate and the recovery rate of polymer with a low water content were more than 96%.