Double network (DN) gels, composed of two interpenetrating polymer networks with contrasting properties, garnered considerable attention since their invention due to large resistances to crack initiation and propagation. This study systematically investigates the effect of viscous solvent on the fracture behavior of DN gels through pre-notch and post-notch crack tests conducted on both water-swollen and ethylene glycol (EG)-swollen DN gels. Fracture energy analysis reveals that the chain dynamics changed by viscous solvent EG would remarkably reduce the two individual fracture energy contributions Γbulk and Γtip, originating from the energy dissipation in the bulk and in the crack tip vicinity, respectively. Furthermore, we observed that chain dynamics influence crack propagation behaviors and the molecular orientation of network strands ahead of crack tips in DN gels. Examination of the retardation patterns ahead of propagating crack tips allows for the analysis of the molecular orientation of network strands. Unusual butterfly-like retardation patterns were observed for the EG-swollen DN gels, in stark contrast to the conventional damage zone patterns seen in water-swollen DN gels. This suggests that the slowed chain dynamics induced by the viscous solvent EG lead to significant viscoelastic mechanical responses ahead of crack tips, which governs the stress/strain fields at the crack tip. This study offers valuable insights into the underlying toughening mechanism of DN gels, particularly regarding the effect of polymer chain dynamics. The experimental analysis, integrating findings on fracture energy contributions, crack propagation behaviors, and retardation observations from both pre-notch and post-notch crack tests, could be applied to characterize other soft materials with diverse toughening mechanisms, thereby aiding in the design and application of future soft materials.

中文翻译：

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粘性溶剂对通过缺口前和缺口后裂纹测试检查的预损伤双网络凝胶断裂的影响


双网络 （DN） 凝胶由两个具有截然不同特性的互穿聚合物网络组成，由于对裂纹萌生和扩展具有很大的抵抗力，自发明以来就引起了相当大的关注。本研究通过对水溶胀和乙二醇 （EG） 溶胀的 DN 凝胶进行缺口前和缺口后裂纹测试，系统地研究了粘性溶剂对 DN 凝胶断裂行为的影响。裂缝能量分析表明，粘性溶剂 EG 改变的链动力学会显着减少两个单独的裂缝能量贡献 Γbulk 和 Γtip，分别源于本体和裂纹尖端附近的能量耗散。此外，我们观察到链动力学会影响 DN 凝胶中裂纹传播行为和网络链的分子取向。在传播裂纹尖端之前检查延迟模式可以分析网络链的分子取向。在 EG 溶胀的 DN 凝胶中观察到不寻常的蝴蝶状延迟模式，这与水溶胀 DN 凝胶中常见的损伤区模式形成鲜明对比。这表明，由粘性溶剂 EG 诱导的缓慢链动力学导致裂纹尖端之前产生显着的粘弹性机械响应，从而控制裂纹尖端的应力/应变场。这项研究为 DN 凝胶的潜在增韧机制提供了有价值的见解，特别是关于聚合物链动力学的影响。 实验分析整合了裂口前和缺口后裂纹测试的断裂能量贡献、裂纹扩展行为和延迟观察结果，可用于表征其他具有不同增韧机制的软材料，从而有助于未来软材料的设计和应用。