Molecular dynamics studying on welding behavior in thermosetting polymers due to bond exchange reactions
Molecular dynamics studying on welding behavior in thermosetting polymers due to bond exchange reactions
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DOI：
10.1039/c5ra26128g
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发表时间：
2016-02
期刊：
影响因子：
3.9
通讯作者：
Hua Yang;Kai Yu;Xiaoming Mu;Yujie Wei;Ya-Fang Guo;H. Qi
中科院分区：
文献类型：
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作者：
Hua Yang;Kai Yu;Xiaoming Mu;Yujie Wei;Ya-Fang Guo;H. Qi
共价适应性网络(或动态共价网络)聚合物可以通过键交换反应改变其网络拓扑结构，从而一个活性原子取代现有键中的一个原子，从而产生一个新的键和一个新的活性原子。这个过程在网络中重复无数次，赋予网络有趣的材料行为，如应力松弛、表面焊接、自我修复和回收。本文用分子动力学模拟方法研究了环氧体系中键交换反应引起的表面焊接问题。两个环氧网络被构建并接触，然后激活键交换反应。跟踪了活性原子的轨迹，显示了活性原子是如何穿过界面的。根据模拟结果，分析了焊接时间、焊接温度、聚合度和原始网络的交联度等焊接条件对焊接材料力学性能的影响。这些参数决定了界面上连接的键合数量，从而影响焊接性能。最终，在足够长的焊接时间下，该系统可以完全恢复与新网络相同的模数和屈服应力。最后，分子动力学模拟得到的活性原子的穿透深度与一些现有理论的预测符合得很好。
Covalent adaptable network (or dynamic covalent network) polymers can alternate their network topology through bond exchange reactions, whereby an active atom replaces an atom in an existing bond, resulting in a new bond and a new active atom. This process repeats itself numerous times in the network, bestowing interesting material behaviors, such as stress relaxation, surface welding, self-healing and recycling, upon the network. In this paper, molecular dynamics simulations are used to investigate surface welding due to bond exchange reactions in an epoxy system. Two epoxy networks are constructed and brought into contact, and bond exchange reactions are then activated. The trajectory of active atoms is tracked, which shows how the active atoms cross the interface. Based on simulation results, this work analyzes the influence of welding conditions, such as welding time, welding temperature, degree of polymerization and crosslinking density of original networks, on the mechanical properties of welded materials. These parameters determine the number of connected bonds on the interface, which consequently affects the welding performance. Eventually, with a sufficiently long welding time, the system can fully recover the same modulus and yielding stress as those of a fresh network. Finally, the active atoms' penetration depth, obtained from MD simulation, shows good agreement with the predictions of some existing theories.