高强韧水凝胶的形变和破坏行为

Deformation and Fracture Behavior of Strong and Tough Hydrogels

水凝胶是一种在水中溶胀的聚合物网络,与生物组织具有结构上的相似性。传统水凝胶中聚合物网络的不均匀性和高含水量使得水凝胶的力学性能较弱,远远低于高强韧的生物组织,限制了其作为结构材料在生物工程等领域的应用。近年来,科研人员在提高水凝胶力学性能方面取得了很大进展,开发了很多高强韧水凝胶,如双网络(DN)水凝胶、动态键水凝胶、缠结远超交联的水凝胶和纤维复合凝胶材料等。本文首先简述了为增强水凝胶力学性能而不断进行的努力,随后介绍了水凝胶强度和韧性的关系,最后根据不同种类高强韧水凝胶的形变和破坏行为,分析其聚合物网络结构中的能量耗散机制,从而解释这些水凝胶高强韧的结构起源。

Hydrogel is a kind of polymer network swelling in water,which has structural similarity with biotissues.Traditional hydrogels are mechanically weak and brittle,due to their inherent heterogeneous microstructures and high water contents,which severely limit their applications.In recent years,researchers have been committed to improving the mechanical properties of hydrogels and have developed many strong and tough hydrogels,such as double-network(DN)hydrogels,dynamic bond hydrogels,hydrogels with rich entanglements,and fiber reinforced soft composites.In this review,we first summarize the development of hydrogels for enhancing mechanical properties and then introduce the relationship between stiffness and toughness of hydrogels.After that,several typical tough and strong hydrogels are selected to introduce their deformation and fracture behaviors,which give a preliminary understanding of the energy dissipation mechanisms of different hydrogels.The mechanisms mentioned in this review include the breakage and reformation of physical bonds,the enhanced crack resistance due to phase-separated structure,the bulk viscoelastic energy dissipation,the near-crack dissipation and the fiber pullout and rupture.Then,the characteristics of these strong and tough hydrogels are summarized as follows:DN hydrogels dissipate energy through chain scission but soften after large deformation;dynamic bond hydrogels show self-healing behavior and large bulk hysteresis;hydrogels with rich entanglements have dense entanglements but sparse cross-links and low hysteresis;fiber reinforced soft composites have multi-scale energy dissipation and very large process zones.