López-Barrón Carlos R, Zhou Huaxing
ExxonMobil Chemical Company, Baytown, Texas 77520, USA.
ExxonMobil Research and Engineering Company, Annandale, New Jersey 08801, USA.
Phys Rev Lett. 2017 Dec 15;119(24):247801. doi: 10.1103/PhysRevLett.119.247801. Epub 2017 Dec 11.
Aromatic π-π interactions between phenyl groups of adjacent chains in poly(4-vinylbiphenyl) (PVBP) have profound effects on the dynamics of this polymer. We report two unexpected nonlinear viscoelastic responses of PVBP when subjected to uniaxial flow. One is the unprecedented observation of extensional strain hardening (SH) in a barely entangled polymer melt. An even more intriguing finding is that SH of lightly (or even barely) entangled melts occurs at strain rates one order of magnitude below the coil-stretch transition predicted by Rouse theory (ϵ[over ˙]{H}=0.5/τ{R}).We postulate that this behavior is due to a molecular rearrangement mechanism (supported by x-ray diffraction measurements) that involves flow-induced π-π stacking of the phenyl groups, which results in an enhancement of the friction coefficient between polymer chains.
聚（4-乙烯基联苯）（PVBP）中相邻链的苯基之间的芳香π-π相互作用对该聚合物的动力学有深远影响。我们报道了PVBP在单轴流动下的两种意外的非线性粘弹性响应。一种是在几乎未缠结的聚合物熔体中前所未有的拉伸应变硬化（SH）现象。一个更有趣的发现是，轻度（甚至几乎没有）缠结熔体的SH出现在应变率比劳斯理论预测的线圈拉伸转变低一个数量级的情况下（ϵ[˙上标]{H}=0.5/τ{R}）。我们推测这种行为是由于一种分子重排机制（由X射线衍射测量支持），该机制涉及流动诱导的苯基π-π堆积，这导致聚合物链之间的摩擦系数增加。
