The nonlinear rheological response to extensional flows in entangled polymers is related to the segmental chain stretching and to the chemical identity of the monomeric units. The latter has a strong effect on the drag coefficients, and therefore, quantification of molecular conformation changes in the subnanometer scale (at the monomer level) are crucial to fully understand nonlinear viscoelastic behavior in polymer melts. We report in situ time-resolved extensional rheo-small-angle neutron scattering (tEr-SANS) and wide-angle X-ray scattering (tEr-WAXS) during startup of uniaxial flow on a monodisperse polystyrene melt. Flow-induced segmental alignment was quantified with tEr-SANS, whereas local alignment of the backbone–backbone and phenyl–phenyl interactions were measured with tEr-WAXS. Linear relations between the three alignment factors and stress were observed at low stresses, which confirmed the validity of simple stress-SANS and stress-WAXS rules (SSR and SWR, respectively). Significant differences in SSR and SWR coefficients, as well as the stress values for failure of the two rules suggest very different correlations between global (at the segmental level) and local (at the monomer level) conformations with stress.

中文翻译：

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拉伸流动启动过程中聚合物链的局部和全局拉伸

缠结聚合物中拉伸流动的非线性流变响应与链段拉伸和单体单元的化学特性有关。后者对阻力系数有很强的影响，因此，亚纳米尺度（单体水平）分子构象变化的量化对于充分理解聚合物熔体中的非线性粘弹性行为至关重要。我们报告了单轴流动在单分散聚苯乙烯熔体上启动期间的原位时间分辨拉伸流变小角中子散射 (tEr-SANS) 和广角 X 射线散射 (tEr-WAXS)。流动诱导的节段排列用 ter-SANS 量化，而骨架-骨架和苯基-苯基相互作用的局部排列用 tEr-WAXS 测量。在低应力下观察到三个对齐因素与应力之间的线性关系，这证实了简单应力-SANS 和应力-WAXS 规则（分别为 SSR 和 SWR）的有效性。SSR 和 SWR 系数的显着差异，以及两种规则失效的应力值表明，全局（在节段水平）和局部（在单体水平）构象与应力之间的相关性非常不同。