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

技术概述：目前的EAGER提案是四所美国机构（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）和一所外国机构（荷兰埃因霍温技术大学）的合作成果。技术目标是详细说明在纠缠聚合物熔体和溶液中报道的流动不稳定性的有效性限制。在传统流变仪中，聚合物流体的流动通常被认为是接近粘度的和稳定的。当不稳定或二次流动发生时，一般认为这种测量不能用于确定材料参数。这在任何实验挑战中都是重要的，例如，分子理论，如聚合物链动力学的重复模型。根据文献中出现的一组新结果，重复理论的实验验证的基础实际上是基于非均匀流的实验。如果这是真的，它将改变非线性变形体系中聚合物流体动力学的范式。然而，许多人对这些结果持怀疑态度，文献中有许多相互矛盾的结果报告。因此，最重要的是建立流动条件（剪切速率和大小）和材料参数（例如，缠结密度）的范围，这些观察结果是正确的，可能出现错误的范围，并以一种结果被广泛接受的方式这样做。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，所有实验都有来自至少三个机构的一名代表。工作的成功被定义为在聚合物溶液和熔体的流动剖面上取得实验室间的共识。客观性是通过多个实验室和多个学生进行不同类型的实验来发展的？中性的眼睛吗?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室进行，其中一个将在所有实验室进行。实验包括粒子跟踪测速、共聚焦显微镜下荧光染料测速和宏观平行板锥与板非线性特性的比较。聚合物流变学的主要范式是还原理论。由于重复是目前聚合物流动的范例，它被广泛应用于工业环境中，以了解如何改变分子参数以取得聚合物加工的进展。重复理论的几个分支也开始在工业中被采用。然而，最近出现了一项强有力的工作来挑战这一范式。它已经报道了强流动不稳定性，这将使与聚合物加工有关的制度中的重复理论失效。因此，确定所报告的流动不稳定性是否发生在工业相关的流量范围内是很重要的。目前的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，荷兰埃因霍温技术大学）的合作者，目标是建立这种流动不稳定发生的实验条件范围。由于一般社区尚未统一接受报告的结果，因此目前的合作将提供重复（用于验证目的）和新颖的实验，以确定报告结果的相关范围，以及它们如何影响当前对聚合物非线性流变学的理解及其在分子（重复）理论中的基础。目前的提议做到了这一点。此外，由于其结构是通过一组创新的学生团队进行协作工作，所有实验都有来自至少三个机构的一名代表。所有学生都将参与与埃因霍温技术大学的合作。

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.