Investigation On The Synthesis And Properties Of Double-network Self-healing Hydrogel Based On H-bond

Polymer hydrogels, containing a large amount of water, are a class of condensed matter cross-linked with chemical bonds or physical nodes. Due to their excellent biocompatibility, hydrogels have been widely used in drug delivery carriers and tissue engineering et.al. Recently, researchs on self-healing hydrogels have been a hot topic, and plenty of self-healing hydrogels based on non-covalent bond have been designed and prepared. However, most reported self-healing hydrogels suffer from low mechanical strength, which largely limit their application in many fields. To address this problem, we have prepared a dual physically cross-linked hydrogel with self-healing ability. The introduction of dual physically cross-linked network contribute to the excellent mechanical properties of the hydrogel, and the hydrogel can be quickly self-healing at room temperature resulted from the dynamic physically cross-linked network. This thesis has finished work as below:1?We have prepared a dual physically cross-linked hydrogel composed of poly(acrylamide-co-acrylic acid)(PAM-co-PAA) and polyvinyl alcohol(PVA) by simple two-steps methods of copolymerization and freezing/thawing. The hydrogen bond-associated entanglement of copolymer chains is formed as crosslinking points to construct the first network. After being subjected to the freezing/thawing treatment, PVA chains are closed to form crystalline domains which serve as knots of the second network. We use XRD and SEM to comfirm the PVA crystalline domains and internal morphology of the hydrogel. The results of tensil tests show that increasing copolymer contents and numbers of freezing/thawing circles make the hydrogel have better mechanical properties. Compared with the PVA/PAM-co-PAA hydrogels consisting of single-network or physically–chemically hybrid cross-linked network, the dual physically cross-linked hydrogel have better mechanical properties, and can be quickly self-healing at room temperature without external stimulis.2?We further study what influence the molar ratio of acrylamide/acrylic acid have on the mechanical properties and self-healing efficiency. By analyzing the transparency of different samples, we have confirmed that the composition of the copolymer has resulted in the change of the internal network structure of the gel. With increasing the content of polyacrylic acid, the PVA crystalline domains decrease, which resulting in dual network structure becoming loose. The strength and toughness of the hydrogels are also in declining. In addition, no matter what kind of mechanical properties to be used to characterize the self-healing efficiency of the hydrogel, the increase of the polyacrylic acid segments in the copolymer is beneficial to the improvement of the self-healing performance of the hydrogel.