We report on the rheology of isotropic and nematic aqueous solutions of a sulfonated all-aromatic polyamide, poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT), that forms high-aspect-ratio rod-like assemblies. For quiescently isotropic solutions, the concentration dependence of the zero-shear viscosity, longest relaxation time, and terminal modulus shows deviations in comparison to the Doi-Edwards theory for hard rods. For quiescently nematic solutions, we characterize the flow behavior through steady-state and transient nonlinear rheological measurements in conjunction with small-angle neutron scattering under shear. The steady-state flow curve is characterized by two anomalous shear thickening responses, one at moderate shear rates and the other immediately prior to flow alignment at high shear rates. We assign the origin of these shear thickening response to director “kayaking” and “out-of-plane steady” states, using predictions from prior high-resolution numerical simulations of sheared nematic rods. Utilizing transient shear flow reversals and step-down experiments, we characterize the oscillatory response of the nematic director through these flow regimes. When the first normal stress difference is plotted versus the shear stress during a transient step-down, the so-called dynamic stress path, the counterclockwise versus clockwise rotation has previously been shown to reveal the relative dominance of viscous versus elastic contributions to the stress tensor, respectively. Our measurements strongly suggest that the anomalous shear thickening behavior in nematic PBDT solutions arises from viscous stresses developed as the ensemble of rods undergoes periodic oscillatory motion under shear, rather than elastic stresses due to broadening of the orientational distribution function.

中文翻译：

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液晶聚电解质的非线性流变学指纹图谱

我们报告了磺化全芳族聚酰胺聚（2,2'-二磺酰基-4,4'-联苯胺对苯二甲酰胺）（PBDT）的各向同性和向列水溶液的流变性，形成高纵横比棒状组件。对于静态各向同性溶液，与硬棒的 Doi-Edwards 理论相比，零剪切粘度、最长松弛时间和终端模量的浓度依赖性显示出偏差。对于静态向列解决方案，我们通过稳态和瞬态非线性流变测量结合剪切下的小角度中子散射来表征流动行为。稳态流动曲线的特点是两种异常的剪切增稠响应，一种在中等剪切速率下，另一个在高剪切速率下流动对齐之前。我们使用先前对剪切向列杆的高分辨率数值模拟的预测，将这些剪切增厚响应的起源归因于导向器“皮划艇”和“平面外稳定”状态。利用瞬态剪切流逆转和降压实验，我们通过这些流态表征向列导向器的振荡响应。当在瞬态下降期间绘制第一个法向应力差与剪切应力时，即所谓的动态应力路径，逆时针与顺时针旋转先前已被证明揭示了粘性与弹性对应力张量的贡献的相对优势， 分别。