Adaptive polymers are being designed with dynamic molecular bonds or chain interactions to respond with external stimuli with unparalleled mechanical properties and multifunctionality. An elegant example is to substantially enhance the stretchability and toughness of hydrogels through the use of ionic bond interactions. To assist the materials design and applications, a predictive theory is in high demand. However, existing multi-scale mechanics models often rely on empirical assumptions and relationships derived from polymer chemistry or physics to describe the evolution of microscale details under external stimuli, which are challenging to be validated experimentally. This study introduces a new methodology to develop constitutive theories for stretchable hydrogels based on insights garnered from molecular dynamics (MD) simulations. The continuum-level viscoelastic theory establishes the thermodynamics framework for stress-strain relationships, while MD simulations inform the evolution mechanisms of microscale bond interactions and network rearrangements, such as the bond distance and network relaxation time. These insights are then properly formulated based on polymer physics principles and fed into the continuum-level model. The resulting constitutive theory closely captures the stress responses at various loading conditions observed in experiments, as well as the microscale system volume and bond distance uncovered in MD simulations. Parametric studies are conducted to investigate the influences of various loading and material parameters on the mechanical properties of the materials, including loading rates, network crosslinking density, maximum strain, and bonding strength. Overall, the study establishes the connection between microscale network structure and mechanical responses of stretchable hydrogels with dynamic ionic bonds. It also offers practical guidance for optimizing material structures and loading conditions to enhance energy absorption and dissipation capabilities. The modeling approach can be extended to the study of other adaptive polymers with different dynamic bonds to create more precise and physically meaningful constitutive models.

中文翻译：

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具有动态离子键的高可拉伸水凝胶的分子模拟引导和物理信息本构模型

自适应聚合物被设计成具有动态分子键或链相互作用，以响应外部刺激，具有无与伦比的机械性能和多功能性。一个很好的例子是通过使用离子键相互作用来显着增强水凝胶的拉伸性和韧性。为了协助材料设计和应用，非常需要预测理论。然而，现有的多尺度力学模型通常依赖于高分子化学或物理学的经验假设和关系来描述外部刺激下微观细节的演变，这很难通过实验验证。这项研究引入了一种新的方法，根据分子动力学（MD）模拟获得的见解，开发可拉伸水凝胶的本构理论。连续介质级粘弹性理论建立了应力-应变关系的热力学框架，而分子动力学模拟则揭示了微观键相互作用和网络重排的演化机制，例如键距和网络弛豫时间。然后，根据聚合物物理原理正确表述这些见解，并将其输入连续体级模型中。由此产生的本构理论密切捕捉了实验中观察到的各种负载条件下的应力响应，以及 MD 模拟中发现的微尺度系统体积和键距。进行参数研究以研究各种载荷和材料参数对材料机械性能的影响，包括载荷速率、网络交联密度、最大应变和粘合强度。总体而言，该研究建立了微尺度网络结构与具有动态离子键的可拉伸水凝胶的机械响应之间的联系。它还为优化材料结构和载荷条件以增强能量吸收和耗散能力提供了实用指导。该建模方法可以扩展到具有不同动态键的其他自适应聚合物的研究，以创建更精确且具有物理意义的本构模型。