Lei Jincheng, Xu Shuai, Li Ziqian, Liu Zishun
International Center for Applied Mechanics, State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi'an Jiaotong University, Xi'an, China.
Front Chem. 2020 Feb 25;8:115. doi: 10.3389/fchem.2020.00115. eCollection 2020.
Meso-scale models for hydrogels are crucial to bridge the conformation change of polymer chains in micro-scale to the bulk deformation of hydrogel in macro-scale. In this study, we construct coarse-grain bead-spring models for polyacrylamide (PAAm) hydrogel and investigate the large deformation and fracture behavior by using Dissipative Particle Dynamics (DPD) to simulate the crosslinking process. The crosslinking simulations show that sufficiently large diffusion length of polymer beads is necessary for the formation of effective polymer. The constructed models show the reproducible realistic structure of PAAm hydrogel network, predict the reasonable crosslinking limit of water content and prove to be sufficiently large for statistical averaging. Incompressible uniaxial tension tests are performed in three different loading rates. From the nominal stress-stretch curves, it demonstrated that both the hyperelasticity and the viscoelasticity in our PAAm hydrogel models are reflected. The scattered large deformation behaviors of three PAAm hydrogel models with the same water content indicate that the mesoscale conformation of polymer network dominates the mechanical behavior in large stretch. This is because the effective chains with different initial length ratio stretch to straight at different time. We further propose a stretch criterion to measure the fracture stretch of PAAm hydrogel using the fracture stretch of C-C bonds. Using the stretch criterion, specific upper and lower limits of the fracture stretch are given for each PAAm hydrogel model. These ranges of fracture stretch agree quite well with experimental results. The study shows that our coarse-grain PAAm hydrogel models can be applied to numerous single network hydrogel systems.
水凝胶的介观尺度模型对于将微观尺度上聚合物链的构象变化与宏观尺度上水凝胶的整体变形联系起来至关重要。在本研究中，我们构建了聚丙烯酰胺（PAAm）水凝胶的粗粒化珠簧模型，并通过使用耗散粒子动力学（DPD）模拟交联过程来研究其大变形和断裂行为。交联模拟表明，聚合物珠子足够大的扩散长度对于有效聚合物的形成是必要的。所构建的模型展示了PAAm水凝胶网络可重现的真实结构，预测了合理的含水量交联极限，并证明对于统计平均来说足够大。在三种不同加载速率下进行了不可压缩单轴拉伸试验。从名义应力 - 拉伸曲线可以看出，我们的PAAm水凝胶模型中既反映了超弹性又反映了粘弹性。三种相同含水量的PAAm水凝胶模型的分散大变形行为表明，聚合物网络的介观构象在大拉伸时主导力学行为。这是因为具有不同初始长度比的有效链在不同时间拉伸至伸直。我们进一步提出了一种拉伸准则，使用C - C键的断裂拉伸来测量PAAm水凝胶的断裂拉伸。使用该拉伸准则，为每个PAAm水凝胶模型给出了断裂拉伸的特定上限和下限。这些断裂拉伸范围与实验结果相当吻合。研究表明，我们的粗粒化PAAm水凝胶模型可应用于众多单网络水凝胶系统。
