Hydrogels with tunable mechanical properties hold significant potential for applications in various fields. Salting-out has proven to be an effective way for substantially and reversibly regulating the mechanical properties of hydrogels. In this study, we explored the evolution of the mechanical behaviors of Polyacrylamide/Chitosan (PAAm/CS) composite hydrogels with salting-out experimentally, and the results indicate that salting-out treatment can increase the tangent modulus by two orders of magnitude and effectively suppress the strain-softening behavior. However, to date, no constitutive model has been developed that can quantitatively describe the variation of hydrogel mechanical properties with salting-out. To quantify the experimental observations, we developed a micromechanism-based constitutive model. In this model, the stress of hydrogel is contributed by the matrix network and the tunable network, with the latter consisting of cluster domains and connecting domains. Based on the microscopic picture, with further salting-out, the modulus of the cluster domain increases and the volume fraction of the cluster domain decreases synergistically, resulting in the evolution of macroscopic properties. The present model captures the mechanical properties of various hydrogels well, and the finite element analysis exhibits ability to predict complex loading conditions. By designing a novel adjustable phononic crystal structure with PAAm/CS hydrogel, it is demonstrated that the current model will play an important role in guiding the preparation of tunable hydrogels and the application for functional devices.

中文翻译：

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通过盐析调节机械性能的水凝胶本构模型

具有可调机械性能的水凝胶在各个领域具有巨大的应用潜力。盐析已被证明是显着且可逆地调节水凝胶机械性能的有效方法。在本研究中，我们通过实验探索了聚丙烯酰胺/壳聚糖（PAAm/CS）复合水凝胶的力学行为随盐析的变化，结果表明盐析处理可以将切线模量提高两个数量级，并且有效抑制应变软化行为。然而，迄今为止，尚未开发出能够定量描述水凝胶力学性能随盐析变化的本构模型。为了量化实验观察结果，我们开发了一种基于微观机制的本构模型。在该模型中，水凝胶的应力由基质网络和可调网络贡献，后者由簇域和连接域组成。从微观上看，随着盐析的进一步进行，团簇域的模量增加，团簇域的体积分数协同减小，导致宏观性质的演变。本模型很好地捕捉了各种水凝胶的机械性能，并且有限元分析表现出预测复杂载荷条件的能力。通过用PAAm/CS水凝胶设计新型可调节声子晶体结构，证明该模型将在指导可调节水凝胶的制备和功能器件的应用方面发挥重要作用。