Collaborative Research: EAGER Proposal on Non-Homogeneous Flow Fields in Nonlinear Rheology: A Challenge to Current Paradigms?

技术总结目前热切的提案是四家美国机构(德克萨斯理工大学、麻省理工学院、康奈尔大学和伊利诺伊理工学院)和一家外国机构(荷兰埃因霍温技术大学)共同努力的结果。其技术目标是详细说明已报道的缠绕聚合物熔体和溶液中流动不稳定性的有效性限度。在常规流变仪中，聚合物流体的流动通常被假定为近乎粘性和稳定的。当发生不稳定或二次流时，通常认为此类测量不能用于确定材料参数。这在对例如诸如聚合物链动力学的旋转模型之类的分子理论的任何实验挑战中都是重要的。根据文献中出现的一组新结果，爬行理论的实验验证的基础实际上是基于非均质流的实验。如果这是真的，它改变了非线性变形区域中聚合物流体动力学的范式。然而，社区中的许多人对这些结果持怀疑态度，文献中有多个相互矛盾的结果的报告。因此，最重要的是确定这种观测正确的流动条件(剪切速率和大小)和材料参数(例如，纠缠密度)的范围，以及可能发生错误的范围，并以社区普遍接受的方式这样做。目前的建议就是为了做到这一点。这些小组通过一组创新的学生团队进行合作，学生团队有来自至少三个机构的一名代表，负责所有实验。这项工作的成功被定义为在实验室之间就聚合物溶液和熔体中的流动情况达成共识。客观性是通过让多个实验室和多个学生进行每种类型的实验来培养的，这样就可以用中立的眼睛？对实验数据的检验有重大影响。将进行三种类型的实验，每种实验将在至少两个实验中进行，其中一个将在所有实验中进行。实验包括粒子跟踪测速仪、共焦显微镜荧光染料测速仪和宏观平行板-锥板与板材的非线性特性比较。非技术总结聚合物流变学的主要范式是旋转理论。由于旋转是目前聚合物流动的范例，它在工业环境中被广泛使用，以了解如何在聚合物加工方面取得进展时改变分子参数。重整理论也有几个分支，正开始在工业中采用。然而，最近的工作似乎正在大力推进，以挑战这一范式。它已经报告了强烈的流动不稳定性，这将在与聚合物加工相关的区域内使旋转理论失效。因此，确定所报告的流动不稳定性是否发生在与工业相关的流速范围内是重要的。本提案汇集了来自四所美国大学和一所外国大学(德克萨斯理工大学、麻省理工学院、康奈尔大学和伊利诺伊理工学院、荷兰埃因霍温工业大学)的合作者，目的是建立发生这种流动不稳定性的实验条件范围。由于一般社区尚未统一接受已报道的结果，本次合作将提供重复的(用于验证目的)和新颖的实验，以确定已报道的结果相关的范围，以及它们如何影响目前对聚合物非线性流变学及其分子(旋转)理论基础的理解。目前的建议做到了这一点。此外，由于它的结构是通过一组创新的学生团队进行合作，学生团队至少有来自三个机构的一名代表参与所有实验。所有学生都将参加与埃因霍温工业大学的合作。

TECHNICAL SUMMARYThe present EAGER proposal is a collaborative effort among four U.S. institutions (Texas Tech University, Massachusetts Institute of Technology, Cornell University and Illinois Institute of Technology) and one foreign institution (Technical University of Eindhoven in the Netherlands). The technical goal is to detail the limits of validity of reported flow instabilities in entangled polymer melts and solutions. The flow of polymer fluids in conventional rheometers is generally assumed to be nearly viscometric and stable. When instability or secondary flows occur, it is generally acknowledged that such measurements cannot be used to determine material parameters. This is important in any experimental challenge to, e.g., a molecular theory such as the reptation model of polymer chain dynamics. According to a new set of results that has appeared in the literature, the basis for the experimental verification of the reptation theory is, in fact, based upon experiments from non-homogeneous flows. If this is true, it changes the paradigm for the dynamics of polymer fluids in nonlinear deformation regimes. However, much of the community is skeptical of these results and there are multiple reports in the literature of contradictory results. Hence, it is paramount to establish the range of both flow conditions (rate and magnitude of shear) and material parameters (e.g., entanglement density) for which such observations are correct and the range where errors may have been made and to do so in a way that the results are accepted by the community at large. The present proposal is constructed to do this. The groups collaborate through an innovative set of student teams having one representative from at least three institutions for all experiments. Success of the work is defined as achieving an interlaboratory consensus of the flow profiles in polymer solutions and melts. Objectivity is developed by having multiple labs with multiple students performing each type of experiment so that ?neutral eyes? have the major influence in the examination of experimental data. Three types of experiments will be performed, each will be performed in at least two labs and one will be performed in all labs. The experiments are particle tracking velocimetry, confocal microscopy fluorescence dye velocimetry and macroscopic parallel plate-cone and plate comparisons of nonlinear properties. NON-TECHNICAL SUMMARYThe major paradigm of polymer rheology is the reptation theory. Because reptation is the present paradigm for polymer flow, it is widely used in industrial settings to understand how to change molecular parameters in making advances in polymer processing. There are several offshoots to reptation theory as well that are beginning to be adopted in industry. Yet, recent work has appeared that is being strongly advanced to challenge this paradigm. It has reported strong flow instabilities which would invalidate the reptation theory in the regime relevant to polymer processing. Hence establishing whether or not the reported flow instabilities occur in industrially relevant ranges of flow rates is important. The present proposal brings together collaborators from four U.S. and one foreign university (Texas Tech University, Massachusetts Institute of Technology, Cornell University and Illinois Institute of Technology,Technical University of Eindhoven in the Netherlands) with the goal of establishing the range of experimental conditions where such flow instabilities occur. Because the general community has not uniformly accepted the reported results, the present collaboration will provide both repeat (for validation purposes) and novel experimentation to establish the range over which the reported results are relevant and how they impact the current understanding of polymer nonlinear rheology and its basis in molecular (reptation) theory. The present proposal does this. In addition, because of its structure as a collaborative work through an innovative set of student teams having one representative from at least three institutions for all experiments. All students will participate in the collaboration with the Technical University of Eindhoven.