Advances in modeling of polymer melt rheology
Advances in modeling of polymer melt rheology
复制标题
聚合物熔体流变学建模的进展
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
Seung Joon Park
中科院分区：
文献类型：
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作者：
R. Larson;Qiang Zhou;S. Shanbhag;Seung Joon Park
预测流变学的理论的发展（即，熔体或溶液状态下的致密填充聚合物的流动）性质是重要的，因为这些理论可以合理设计用于将聚合物成型为产品的聚合物加工方法，并且因为它们可以用于聚合物分子量和长链支化的流变学表征。这些都是重要的课题，因为每年生产的聚合物数量巨大（数以亿计磅）。de Gennes、Doi和Edwards在20世纪70年代后期的开创性工作确立了他们的“管模型”作为预测聚合物流变性能的标准理论。“管"的概念源于这样一个概念，即在致密熔体中，长聚合物与其相邻聚合物的缠结将聚合物的运动限制在”管状“区域-见图1a。直到最近，密集的长链之间的“纠缠”产生了一个限制每条链运动的现象学“管”，无法通过实验成像或模拟，也无法从微观物理学中严格推导出它们的存在，因此接受管模型并非没有争议。此外，在早期，管模型的大多数预测几乎不比定性更好。尽管如此，人们普遍认识到，早期，尽管它的局限性，土井-爱德华兹“管”提供了一个合理的解释，定性地理解线性聚合物在纠缠状态下如何放松，即，他们放松的“爬行”或滑动的链沿着其管轴，并通过收回管内。此外，管模型提供了最大的希望，最终达到定量了解聚合物熔体流变学。自1978年以来，人们一直在努力改进土井-爱德华兹模型。广义地说，20世纪80年代见证了对“连续路径波动”问题的持续攻击-即由于管中链的手风琴式运动而导致的管长度的变化，以及“约束释放”-即由于限定管的周围链的运动而导致的缠结的损失。人们发现，只要链在缠结丢失之前“感觉到”管的存在，就可以将链的松弛描述为在管中爬行，其中管本身由于损失而在空间中移动，并且与周围的移动的链重新产生缠结。这种管运动（现在称为“约束释放劳斯运动”）对于多分散聚合物尤其重要，其中通过围绕短链施加在长链上的缠结可以相当迅速地松弛，并且因此增强含有长链的管的移动性。最后，在某些情况下，如果周围的链比管中的链移动的多得多，以至于它们充当“动态稀释”缠结密度的“溶剂"，则可以认为管直径是连续膨胀或”扩张的“。将约束释放合并到管模型中的这些方法具有透视
T he development of theories to predict the rheological (i.e., flow) properties of densely packed polymers in the melt or solution state is important because such theories might enable rational design of polymer processing methods for shaping polymers into products, and because they can be used in rheological characterization of polymer molecular weight and long-chain branching. These are important topics, given the enormous volume of polymers produced each year (100’s of billions of pounds).The seminal work of de Gennes and Doi and Edwards in the late 1970s established their ‘‘tube model’’ as the standard theory for predicting polymer rheological properties. The ‘‘tube’’ idea arises from the notion that entanglements of a long polymer with its neighbors in a dense melt restrict motion of the polymer to a ‘‘tubelike’’ region — see Figure 1a. Until very recently, the ‘‘entanglements’’ between densely packed long chains that produce a phenomenological ‘‘tube’’ constraining the motion of each chain could not be experimentally imaged or simulated, nor could their existence be rigorously derived from microscopic physics, and so acceptance of the tube model has not come without controversy. In addition, most predictions of the tube model in the early years were hardly better than qualitative. Still, it was generally recognized early on that, despite its limitations, the Doi-Edwards ‘‘tube’’ provides a plausible ansatz for understanding qualitatively how linear polymers in the entangled state relax, namely, they relax by ‘‘reptation’’ or sliding of the chain along its tube axis, and by retraction within the tube. Moreover, the tube model offered the greatest hope for eventually attaining a quantitative understanding of polymer melt rheology. In the years since 1978, many efforts have been made to improve upon the Doi-Edwards model. Broadly speaking, the 1980s witnessed a sustained attack on the problems of ‘‘primitive-path fluctuations’’ — that is, changes in the length of the tube due to accordion-like motions of the chain in the tube, and of ‘‘constraint release’’ — that is, loss of entanglements due to motions of the surrounding chains that define the tube. It was found that as long as the chain ‘‘feels’’ the existence of the tube before the entanglements are lost, one can describe the chain’s relaxation as reptation in a tube, where the tube itself is moving through space due to loss, and recreation of entanglements with surrounding mobile chains. This tube movement (now called ‘‘constraint release Rouse motion’’) is especially significant for polydisperse polymers, where the entanglements imposed on long chains by surrounding short chains can relax quite rapidly, and, hence, enhance the mobility of the tube containing the long chain. Finally, in some cases, one can regard the tube diameter to be continuously expanding or ‘‘dilating,’’ if the surrounding chains are so much more mobile than the chain in the tube that they act as ‘‘solvent’’ that ‘‘dynamically dilutes’’ the entanglement density. These ways of incorporating constraint release into tube models have Perspective