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A network model of transient polymers: exploring the micromechanics of nonlinear viscoelasticity
Soft Matter ( IF 2.9 ) Pub Date : 2021-08-06 , DOI: 10.1039/d1sm00753j Robert J Wagner 1 , Ethan Hobbs 1 , Franck J Vernerey 1
Soft Matter ( IF 2.9 ) Pub Date : 2021-08-06 , DOI: 10.1039/d1sm00753j Robert J Wagner 1 , Ethan Hobbs 1 , Franck J Vernerey 1
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Dynamic networks contain crosslinks that re-associate after disconnecting, imparting them with viscoelastic properties. While continuum approaches have been developed to analyze their mechanical response, these approaches can only describe their evolution in an average sense, omitting local, stochastic mechanisms that are critical to damage initiation or strain localization. To address these limitations, we introduce a discrete numerical model that mesoscopically coarse-grains the individual constituents of a dynamic network to predict its mechanical and topological evolution. Each constituent consists of a set of flexible chains that are permanently cross-linked at one end and contain reversible binding sites at their free ends. We incorporate nonlinear force–extension of individual chains via a Langevin model, slip-bond dissociation through Eyring's model, and spatiotemporally-dependent bond attachment based on scaling theory. Applying incompressible, uniaxial tension to representative volume elements at a range of constant strain rates and network connectivities, we then compare the mechanical response of these networks to that predicted by the transient network theory. Ultimately, we find that the idealized continuum approach remains suitable for networks with high chain concentrations when deformed at low strain rates, yet the mesoscale model proves necessary for the exploration of localized stochastic events, such as variability of the bond kinetics, or the nucleation of micro-cavities that likely conceive damage and fracture.
中文翻译：
瞬态聚合物的网络模型：探索非线性粘弹性的微观力学
动态网络包含在断开连接后重新关联的交联，赋予它们粘弹性。虽然已经开发了连续介质方法来分析它们的机械响应，但这些方法只能在平均意义上描述它们的演变，省略了对损伤起始或应变定位至关重要的局部随机机制。为了解决这些限制，我们引入了一种离散数值模型，该模型对动态网络的各个成分进行细观粗粒度化，以预测其机械和拓扑演变。每个成分由一组在一端永久交联的柔性链组成，并在其自由端包含可逆结合位点。我们结合各条链的非线性力-延伸通过Langevin 模型、通过 Eyring 模型的滑移键解离以及基于标度理论的时空相关键连接。在一系列恒定应变率和网络连接性下将不可压缩的单轴张力应用于代表性体积元素，然后我们将这些网络的机械响应与瞬态网络理论预测的机械响应进行比较。最终，我们发现理想化的连续介质方法仍然适用于在低应变率下变形时具有高链浓度的网络，但中尺度模型证明对于局部随机事件的探索是必要的，例如键动力学的可变性或成核可能会造成损坏和断裂的微腔。
更新日期：2021-09-16
中文翻译：
瞬态聚合物的网络模型：探索非线性粘弹性的微观力学
动态网络包含在断开连接后重新关联的交联，赋予它们粘弹性。虽然已经开发了连续介质方法来分析它们的机械响应，但这些方法只能在平均意义上描述它们的演变，省略了对损伤起始或应变定位至关重要的局部随机机制。为了解决这些限制，我们引入了一种离散数值模型，该模型对动态网络的各个成分进行细观粗粒度化，以预测其机械和拓扑演变。每个成分由一组在一端永久交联的柔性链组成，并在其自由端包含可逆结合位点。我们结合各条链的非线性力-延伸通过Langevin 模型、通过 Eyring 模型的滑移键解离以及基于标度理论的时空相关键连接。在一系列恒定应变率和网络连接性下将不可压缩的单轴张力应用于代表性体积元素，然后我们将这些网络的机械响应与瞬态网络理论预测的机械响应进行比较。最终，我们发现理想化的连续介质方法仍然适用于在低应变率下变形时具有高链浓度的网络，但中尺度模型证明对于局部随机事件的探索是必要的，例如键动力学的可变性或成核可能会造成损坏和断裂的微腔。
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