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Rheo-optical experiments and modeling studies of entangled polymer solutions in steady and transient shear flows.

机译：稳态和瞬态剪切流中纠缠聚合物溶液的流变光学实验和建模研究。

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The goal of this work is to understand the rheology of entangled polymer solutions when subjected to nonlinear viscoelastic deformations characteristic of polymer processing applications. Experimentally, we consider two narrow molecular weight distribution entangled polymer solutions that vary only by their concentration (or number of entanglements per chain). These solutions are subjected to steady and transient shear flows, including startup from rest, double-step shear rate, reversing step shear rate, and relaxation. Data for the average orientation angle and birefringence of these materials are obtained using a phase-modulated flow birefringence apparatus. The results provide information about the degree of orientation and stretch induced by the flow. Of particular interest are the double-step shear rate results, where we observe short time scale over- and undershoots in the orientation angle when the shear rate is increased or decreased, a feature we ascribe to transient chain stretching.; We compare experimental results with predictions generated by the Doi-Edwards-Marrucci-Grizzuti (DEMG) reptation model. We also performed calculations of the model with convective constraint release and contour length fluctuation mechanisms added. These ideas have been suggested as a means of reducing the effective disengagement time and enhancing the rate of orientation relaxation. Surprisingly, the basic Doi-Edwards (DE) model without explicit chain stretching is able to qualitatively capture over- and undershoots in the orientation angle in double-step shear rate flows. When both CCR and CLF are included the model, steady state and transient orientation angle predictions are improved relative to the experimental data; however, the magnitude of the predicted birefringence is shifted to lower values as a result of the reduced orientational anisotropy, suggesting that additional physics, such as tube deformation, might be relevant to inducing residual stress for Weissenberg number based on the longest Rouse time less than O(1).
机译：这项工作的目的是了解当聚合物加工应用发生非线性粘弹性变形时，缠结的聚合物溶液的流变性。实验上，我们考虑了两种窄分子量分布的缠结聚合物溶液，它们仅因其浓度（或每条链的缠结数）而变化。这些溶液经受稳定且短暂的剪切流，包括从静止开始，双步剪切速率，反向步剪切速率和松弛。这些材料的平均取向角和双折射的数据是使用调相流双折射设备获得的。结果提供了有关流动引起的取向和拉伸程度的信息。尤其令人感兴趣的是双步剪切速率结果，其中当剪切速率增大或减小时，我们观察到取向角的短时间尺度上冲和下冲，这归因于瞬时链拉伸。我们将实验结果与Doi-Edwards-Marrucci-Grizzuti（DEMG）复制模型生成的预测进行比较。我们还执行了对流约束释放和轮廓长度波动机制的模型计算。已经提出这些想法作为减少有效脱离时间和提高取向松弛速率的手段。出乎意料的是，基本的Doi-Edwards（DE）模型无需显式的链条拉伸就可以定性地捕获双步剪切速率流中取向角的上冲和下冲。当同时包含CCR和CLF模型时，相对于实验数据，稳态和瞬态取向角的预测将得到改善；然而，由于方向各向异性的减小，预计的双折射的幅度被移到了较低的值，这表明基于最长的Rouse时间小于，附加的物理现象（例如管变形）可能与诱导Weissenberg数的残余应力有关。 O （1）。

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