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Poroelastic fracture of polyacrylamide hydrogels: Enhanced crack tip swelling driven by chain scission
Journal of the Mechanics and Physics of Solids ( IF 5.0 ) Pub Date : 2024-11-12 , DOI: 10.1016/j.jmps.2024.105954
Qifang Zhang, Junjie Liu, Gang Zhang, Yuhong Li, Nan Hu, Jinglei Yang, Yan Yang, Shaoxing Qu, Qianhua Kan, Guozheng Kang

The deformation of hydrogels is accompanied by water migration, a process that plays a crucial role in their fracture behaviors. Previous investigations primarily focus on how the water migration between the environment and hydrogel affects the fracture of hydrogels. Herein, a novel mechanism of the rate-dependent fracture of hydrogels induced by interior water migration is uncovered. Notched polyacrylamide (PAAm) hydrogels are stretched at various stretch rates in both oil and deionized (DI) water environments. Notably, the critical stretches to crack propagation are positively correlated with the stretch rates in both the two environments. This rate-dependent fracture is attributed to the crack tip swelling of PAAm hydrogels. Delayed fracture tests conducted in oil further verify the co-existence of delayed fracture and rate-dependent fracture resulted from interior water migration in PAAm hydrogels. The experimental findings are interpreted by considering the imperfection of a real polymer network, in which the scission of short chains in the region neighboring the crack tip reduces the average crosslinking density locally, thereby greatly amplifying the degree of crack tip swelling and its influence on the fracture of hydrogels. A constitutive model coupling the evolution of polymer network and the diffusion of water molecules is proposed, which can predict the crack tip swelling of notched PAAm hydrogels through the finite element method. Assuming that the decrease in fracture toughness is positively related to the swelling along the crack propagation surface, the predicted normalized fracture toughness matches the experimental results of PAAm hydrogels stretched in water well, and satisfies those in oil environment qualitatively. This work highlights the significant influence of interior water migration on the fracture of hydrogels and provides insights that may guide the design of hydrogels with enhanced fracture resistance.

中文翻译:


聚丙烯酰胺水凝胶的多孔弹性断裂:断链驱动的裂纹尖端膨胀增强



水凝胶的变形伴随着水迁移,这一过程在其断裂行为中起着至关重要的作用。以前的研究主要集中在环境和水凝胶之间的水迁移如何影响水凝胶的断裂。在此,揭示了内部水迁移诱导的水凝胶速率依赖性断裂的新机制。缺口聚丙烯酰胺 (PAAm) 水凝胶在油和去离子 (DI) 水环境中以不同的拉伸速率拉伸。值得注意的是,裂纹扩展的临界拉伸与两种环境中的拉伸速率呈正相关。这种速率依赖性断裂归因于 PAAm 水凝胶的裂纹尖端膨胀。在油中进行的延迟断裂测试进一步验证了 PAAm 水凝胶中内部水迁移导致的延迟断裂和速率依赖性断裂的共存。通过考虑真实聚合物网络的缺陷来解释实验结果,其中裂纹尖端附近区域的短链断裂降低了局部的平均交联密度,从而大大放大了裂纹尖端膨胀的程度及其对水凝胶断裂的影响。提出了一种耦合聚合物网络演化和水分子扩散的本构模型,该模型可以通过有限元方法预测缺口 PAAm 水凝胶的裂纹尖端膨胀。假设断裂韧性的降低与裂纹扩展表面的膨胀呈正相关,则预测的归一化断裂韧性与PAAm水凝胶在水中拉伸的实验结果相匹配,在质量上满足油环境中的实验结果。 这项工作强调了内部水迁移对水凝胶断裂的显着影响,并提供了可能指导设计具有增强抗断裂性的水凝胶的见解。
更新日期:2024-11-12
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