Nonlinear rheology and dynamics of supramolecular polymer networks formed by associative telechelic chains under shear and extensional flows
Nonlinear rheology and dynamics of supramolecular polymer networks formed by associative telechelic chains under shear and extensional flows
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DOI：
10.1122/1.5120897
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发表时间：
2020-05-01
影响因子：
3.3
通讯作者：
Wang, Zuowei
中科院分区：
文献类型：
--
作者：
Amin, Dipesh;Wang, Zuowei
采用非平衡态计算机模拟方法研究了缔合遥爪链和非缔合遥爪链形成的超分子网络的剪切和拉伸流动行为。缔合末端单体或粘着剂的可逆键合导致形成交联的瞬态网络，从而使SPN的机械性能比它们的熔融对应物更强。在启动剪切中，SPN和熔体体系的瞬态剪切粘度η（t）和第一法向应力系数Psi（1）（t）均显示出超调行为，但只有SPN在高剪切速率下表现出瞬态应变硬化。在启动平面拉伸流动中，所有系统都表现出典型的拉伸应变硬化行为。SPN的瞬时拉伸粘度η（E）（t）在进入稳态之前经历小的过冲，这在非缔合聚合物熔体中没有观察到。对于两种类型的聚合物系统与非缠结和弱缠结的链长，稳态剪切粘度表现出典型的剪切稀化行为，而稳态拉伸粘度表现出拉伸硬化，这是与发表的模拟和实验工作。所观察到的流动行为可以从所研究的所有聚合物系统中的流动诱导的非高斯链拉伸和链段取向以及SPN中的附加松弛机制（包括流动诱导的弹性活性股线密度的降低、粘附物交换其相关伙伴的概率的增加、以及在高应变率下平均粘性粘结寿命的降低。(c)2020年流变学学会。
Nonequilibrium computer simulations have been applied to study the shear and extensional flow behavior of supramolecular polymer networks (SPNs) formed by unentangled and weakly entangled associative telechelic chains and their nonassociative polymer melt counterparts. The reversible bonding of the associative end monomers or stickers leads to the formation of percolated transient networks and consequently stronger mechanical properties of the SPNs than their melt counterparts. In startup shear, the transient shear viscosities eta(t) and first normal stress coefficients Psi(1)(t) of both the SPN and melt systems show overshoot behavior, but only the SPNs demonstrate transient strain hardening at high shear rates. In startup planar extensional flows, all systems demonstrate the characteristic extensional strain hardening behavior. The transient extensional viscosities eta(E)(t) of the SPNs undergo a small overshoot before entering the steady state, which was not observed in the nonassociative polymer melts. For both types of polymer systems with unentangled and weakly entangled chain lengths, the steady-state shear viscosities show typical shear-thinning behavior, while the steady-state extensional viscosities demonstrate extension hardening, which are consistent with published simulation and experimental works. The observed flow behavior can be well understood from the flow-induced non-Gaussian chain stretching and segment orientation in all polymer systems studied, as well as the additional relaxation mechanisms in the SPNs, including the flow-induced reduction in the density of elastically active strands, the increment in the probability for the stickers to exchange their associated partners, and the reduction in the average sticky bond lifetimes at high strain rates. (c) 2020 The Society of Rheology.