Network structure and viscoelastic behavior of high-strength crystal microphase crosslinking hydrogels analyzed from combined model

The design of network structure is vital to the preparation of high-strength hydrogels. Using a mechanical model to analyze the network structure and mechanical behavior of hydrogel is an effective means to study the strengthening mechanism of the hydrogel. In this work, a series of acrylonitrile copolymer hydrogels based on crystal microphase crosslinking are synthesized. On this basis, a combined model that consists of the Upper Convected Maxwell model and an ideal spring model is established, which separates the crystal microphase crosslinking network (elastic) from the physical crosslinking network (viscoelastic) based on dipole–dipole interaction. The good fit of the simulated curves to the experimental curves demonstrates that the mechanical behaviors of these hydrogels could be well expressed by such a combined model. The contributions of the two networks to the nominal stress are calculated respectively, and the crosslink densities of the two networks are also compared. It is found that the crosslink density of the viscoelastic network in the hydrogel is higher than that of the elastic network, which further confirms the fact that there is a microphase crosslinking structure in the hydrogel. In addition, the effects of acrylic acid feed ratio, molecular weight and zinc chloride concentration on the network structure of the hydrogel are discussed.