Understanding of Transient Rheology in Step Shear and Its Implication To Explore Nonlinear Relaxation Dynamics of Interphase in Compatible Polymer Multi-microlayered Systems,Industrial & Engineering Chemistry Research

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Understanding of Transient Rheology in Step Shear and Its Implication To Explore Nonlinear Relaxation Dynamics of Interphase in Compatible Polymer Multi-microlayered Systems
Industrial & Engineering Chemistry Research ( IF 3.8 ) Pub Date : 2018-06-01 , DOI: 10.1021/acs.iecr.8b00972
Huagui Zhang ₁ , Khalid Lamnawar ₂ , Abderrahim Maazouz _{2,

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Affiliation

In the industry of polymer coextrusion processing, efforts are being made toward a better control of multilayer flow stability that is governed by the interface/interphase between neighboring layers, the understanding of which is considerably inadequate. This study aims to explore the relaxation dynamics of polymer chains located in the interphase between two compatible polymer melts based on transient rheology in step shear experiments, an area that is often overlooked without justification. First, transient rheology was investigated based on pure polymers of poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF) melts, focusing on a feature of abrupt stress decline observed in the transient period after a large step shear. This feature is considered to be the phenomenological onset of rheological nonlinearity (e.g., stress damping) commonly observed in the long-time window of a relaxation for an entangled polymer. From the molecular viewpoint, the nonlinearity onset is a result of polymer chain disentanglement under a large flow as interpreted based on a refined version of the Doi–Edwards tube model and Wang’s force imbalance theory, etc. A decreased entanglement number of polymer chains, either by decreasing molar mass in the melts or by reducing polymer concentration in solutions, was demonstrated to accelerate the onset of the rheological nonlinearity. In particular, a noticeable stress break-off in the transient period can be observed upon large deformations in the solutions due to their very weak entanglements. Second, large step shears were given to PMMA/PVDF bilayer-structured melts and a new model has been developed to determine the relaxation behavior of the interphase triggered between the layered polymers. Similar to the solutions, an abrupt stress decline was observed in the transient period for the interphase upon a large step deformation, indicating an analogous entanglement weakness of the interphase to the solution. Hence, a close correlation can be established between the interphase and the pure melts and solutions based on their transient rheology and the concept that the polymer chain entanglements can be weakened either by solvent dilution or by blending with dissimilar chains.

中文翻译：

理解阶跃剪切中的瞬变流变学及其对兼容聚合物多微层系统中相间非线性弛豫动力学的启示

在聚合物共挤出加工工业中，人们正在努力更好地控制由相邻层之间的界面/中间相控制的多层流动稳定性，对此的理解是相当不足的。这项研究的目的是基于分步剪切实验中的瞬变流变学，探索位于两个相容的聚合物熔体之间的相中的聚合物链的弛豫动力学，该区域经常被无理地忽略。首先，研究了基于聚甲基丙烯酸甲酯（PMMA）和聚偏二氟乙烯（PVDF）熔体的纯聚合物的瞬变流变学，重点是在大阶跃剪切后的瞬变期间观察到的突然应力下降的特征。该特征被认为是流变非线性的现象学开始（例如，应力衰减）通常在缠结的聚合物的弛豫的长时间窗口中观察到。从分子的角度来看，非线性的出现是聚合物链在大流量下发生纠缠的结果，这是根据改进的Doi–Edwards管模型和Wang的力不平衡理论等解释的。聚合物链的纠缠数减少，或者通过降低熔体中的摩尔质量或通过降低溶液中的聚合物浓度，已证明可加速流变非线性的发生。特别是，由于溶液非常弱的缠结，在溶液中发生较大变形时，可以观察到过渡时期的明显应力折断。第二，对PMMA / PVDF双层结构熔体进行了大的阶梯剪切，并开发了一种新的模型来确定层状聚合物之间触发的相间弛豫行为。与溶液相似，在较大的阶跃变形下，在过渡相的过渡期中观察到了突然的应力下降，表明相间与溶液的缠结相似。因此，基于它们的瞬时流变学和可以通过溶剂稀释或通过与异链混合来减弱聚合物链缠结的概念，可以在中间相与纯熔体和溶液之间建立紧密的联系。在较大的阶跃变形下，在过渡相的过渡期中观察到了突然的应力下降，这表明了相间与溶液的类似缠结弱点。因此，基于它们的瞬时流变学和可以通过溶剂稀释或通过与异链混合来减弱聚合物链缠结的概念，可以在中间相与纯熔体和溶液之间建立紧密的联系。在较大的阶跃变形下，在过渡相的过渡期中观察到了突然的应力下降，这表明了相间与溶液的类似缠结弱点。因此，基于它们的瞬时流变学和可以通过溶剂稀释或通过与异链混合来减弱聚合物链缠结的概念，可以在中间相与纯熔体和溶液之间建立紧密的联系。

更新日期：2018-06-01

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