To explain the nonuniversality in extensional rheology of different polymer melts, contrary ideas, i.e., flow-induced friction reduction and flow-induced friction enhancement, have been proposed during the past decade. Here, we investigate this issue through an interesting case of poly(2-vinyl naphthalene) (P2VN). P2VN has very rigid naphthyl side groups, which may lead to flow-induced friction reduction. At the same time, the naphthyl groups also form strong π–π stacking, which may lead to flow-induced friction enhancement. By combining extensional rheology and wide-angle X-ray scattering, we show that P2VN exhibits flow-induced friction enhancement due to stronger π–π stacking along the flow direction. The result of P2VN is also compared with polystyrene (PS) and poly(4-vinyl biphenyl) (PVBP), which contain aromatic rings in their side groups as well. It is found that the configuration of the flow-induced π–π stacking in P2VN is different from that in PS and PVBP.

中文翻译：

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含有芳香环的化学侧基的影响：流动引起的摩擦增强或减少


为了解释不同聚合物熔体拉伸流变学的非普遍性，在过去十年中提出了相反的想法，即流动诱导摩擦减少和流动诱导摩擦增强。在这里，我们通过一个有趣的聚（2-乙烯基萘）（P2VN）案例来研究这个问题。 P2VN 具有非常刚性的萘基侧基，这可能会导致流动引起的摩擦减少。同时，萘基也形成强烈的π-π堆积，这可能导致流动引起的摩擦增强。通过结合拉伸流变学和广角 X 射线散射，我们发现 P2VN 由于沿流动方向更强的 π-π 堆积而表现出流动诱导的摩擦增强。 P2VN 的结果还与聚苯乙烯（PS）和聚（4-乙烯基联苯）（PVBP）进行了比较，后者的侧基也含有芳香环。研究发现，P2VN 中的流致 π-π 堆积的构型与 PS 和 PVBP 中的不同。