Test of Orientation/Stretch- Induced Reduction of Friction via Primitive Chain Network Simulations for Polystyrene, Polyisoprene, and Poly(n-butyl acrylate)
Test of Orientation/Stretch- Induced Reduction of Friction via Primitive Chain Network Simulations for Polystyrene, Polyisoprene, and Poly(n-butyl acrylate)
复制标题
通过聚苯乙烯、聚异戊二烯和聚丙烯酸正丁酯的原始链网络模拟进行取向/拉伸引起的摩擦减少测试
DOI：
10.1021/ma5016165
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发表时间：
2014
期刊：
影响因子：
5.5
通讯作者：
and H. Watanabe
中科院分区：
文献类型：
--
作者：
Y. Masubuchi;Y. Matsumiya;and H. Watanabe
聚合物在快速拉伸下的纠缠动力学尚未完全了解。也就是说，缠结聚苯乙烯（PS）的解决方案的稳态单轴拉伸粘度的增加与应变速率以上的倒数劳斯时间的增加，而PS熔体的粘度单调下降，即使在这样的高速率。溶液和熔体之间的这种质的差异已被假设为是由取向/拉伸引起的摩擦减少（SORF）引起的。本研究探讨了窄分布的PS，聚异戊二烯（PI），聚（丙烯酸正丁酯）（PnBA）的SORF机制的普遍性。为此目的，通过PS的摩擦降低幅度和拉伸/取向顺序参数之间的经验关系将SORF并入多链滑动链接模拟中[在Macromolecules 2012，45，2773-2782中报道]。这种经验的SORF关系采用了平均场的观点，聚合物主链和溶剂之间的接触，和具有这种平均场功能的模拟被证实，再现令人满意的瞬态和稳态拉伸粘度数据的PS熔体和溶液。假设SORF的大小对聚合物的化学结构不敏感，我们进一步对PI和PnBA的SORF关系进行了模拟。对于PI，模拟合理地描述了熔体和溶液的粘度数据。然而，对于PnBA熔体，数据很好地描述了模拟，但没有SORF。这一结果表明，SORF的大小不是普遍的，但随着聚合物的化学结构的变化。具体地，对于PnBA，柔性侧链总是围绕PnBA主链，并且可以表现为溶剂以屏蔽主链片段之间的直接相互作用，即使在熔体中。在这种情况下，平均场型SORF关系明显失效。然而，即使在快速伸长下，非平均场型SORF也可能导致可忽略的摩擦减少，从而允许没有SORF的模拟来描述PnBA的数据。
Entanglement dynamics of polymers under fast elongation has not been fully understood. Namely, the steady-state uniaxial elongational viscosity of entangled polystyrene (PS) solutions increases with an increase of strain rate above the reciprocal Rouse time, whereas the viscosity of PS melts monotonically decreases even at such high rates. This qualitative difference between solution and melt has been hypothesized to result from the orientation/stretch-induced reduction of friction (SORF). This study examines universality of the mechanism of SORF for narrowly distributed PS, polyisoprene (PI), and poly(n-butyl acrylate) (PnBA). For this purpose, SORF was incorporated in the multichain slip-link simulation through an empirical relationship between the magnitude of friction reduction and the stretch/orientation order parameter for PS [reported in Macromolecules 2012, 45, 2773–2782]. This empirical SORF relationship adopted a mean-field view for contacts between polymer backbone and solvent, and the simulation having this mean-field feature was confirmed to reproduce satisfactorily the transient and steady elongational viscosity data for PS melts and solutions. Assuming that the magnitude of SORF is insensitive to the chemical structure of polymers, we further made the simulation with the same SORF relationship for PI and PnBA. For PI, the simulation reasonably described the viscosity data of a melt and solutions. However, for PnBA melt, the data were well described by the simulation but without SORF. This result suggests that the magnitude of SORF is not universal but changes with the chemical structure of polymers. Specifically, for PnBA, the flexible side chains always surround the PnBA backbone and may behave as a solvent to screen the direct interaction between the backbone segments even in melt. For this case, the mean-field type SORF relationship obviously fails. Nevertheless, a non-mean-field type SORF could result in negligible friction reduction even under fast elongation, thereby allowing the simulation without SORF to describe thet data for PnBA.