Structural Dynamics of Polymer and Surfactant Solutions in Planar Extensional Flow Using In Situ X-ray Scattering

聚合物和其他复杂流体的非牛顿性质源于流动引起的分子和介观结构变化。该建议描述了一项研究计划，其中心是创造和应用新的X射线散射能力，用于研究在交叉缝隙流动装置的停滞点产生的平面伸展流动中的流动流体。以前在这种脉络中应用X射线和中子散射的努力受到流动池结构设计折衷的限制，这些折衷导致运动不均匀和寄生剪切梯度的虚假效应。利用先进光子源(APS)的能力，这里提出的设计概念在应用流场的清晰度方面提供了显著的改进。虽然所开发的方法将广泛适用于许多类型的复杂流体，但我们提出了两个初步研究目标：粘弹性蠕虫状胶束溶液的结构动力学，以及柔性聚合物在稀溶液中的变形。智力优势：蠕虫状表面活性剂胶束的粘弹性溶液通常被视为稀溶液和缠绕聚合物的模型，但也显示出由微观结构变化驱动的各种流动转变和不稳定性的倾向。对定义明确的伸展流动诱导的胶束取向进行量化的能力将有助于对这些流体中的许多现象提供有价值的见解，包括与湍流减阻相关的结构形成、剪切带状和非带状胶束配方之间的差异、某些胶束体系中应变硬化的起源，以及浓缩胶束溶液中流动诱导向列相转变的本质。拉伸流动中聚合物稀溶液的测量是X射线散射的一项非常具有挑战性的应用，但有可能解决大线圈变形的理论预测(和最近的DNA直接可视化)与先前使用光散射测量的线圈大小之间的长期差异。了解剪切流动，特别是伸展流动中的复杂流体流变性，是了解这些技术和其他技术中出现的更复杂流动的先决条件。因此，本文提出的直接测量平面伸展流动中微观流体结构的方法具有巨大的潜力，对社会上重要的技术具有积极的影响。此外，该项目将在科学基础设施和人力资源开发方面产生广泛影响。PI在开发用于流动下聚合物的X射线散射研究的新型仪器方面拥有丰富的经验，这得益于他在APS的DND-CAT研究设施的积极参与。更重要的是，他在向科学合作者以及通过“普通用户”建议访问APS设施的同步加速器用户社区提供这种仪器方面也有记录。以类似的方式，该项目开发的仪器将提供给更广泛的研究界，扩大该项目在将要进行的研究以及对研究生和博士后研究人员培训方面的好处。

Burghardt, Wesley 1336269The non-Newtonian properties of polymers and other complex fluids stem from molecular- and meso-scale structural changes induced by flow. This proposal describes a research program centered on creation and application of novel x-ray scattering capabilities for studying mobile fluids in a planar extensional flow produced at the stagnation point of a cross-slot flow device. Prior efforts to apply x-ray and neutron scattering in this vein have been limited by design compromises in flow cell construction that result in kinematic inhomogeneity and spurious effects of parasitic shear gradients. Exploiting capabilities of the Advanced Photon Source (APS), the design concept proposed here provides a marked improvement in the definition of the applied flow field. While the methods to be developed here will have broad applicability to many classes of complex fluids, two targets are proposed for initial study: structural dynamics of viscoelastic wormlike micelle solutions, and the deformation of flexible polymers in dilute solution.Intellectual Merit :Viscoelastic solutions of wormlike surfactant micelles are often viewed as models of both dilute and entangled polymers, but also show a propensity for a variety of flow transitions and instabilities driven by microscopic structural changes. The ability to quantify micellar orientation induced by a well-defined extensional flow will contribute valuable insights into many phenomena in these fluids, including structure formation associated with turbulent drag reduction, differences between shear-banding and non-banding micelle formulations, the origins of strain hardening in certain micellar systems, and the nature of flow-induced nematic phase transitions in concentrated micelle solutions. Measurement of dilute polymer solutions in extensional flow is a very challenging application for x-ray scattering, but has the potential to address a long-standing discrepancy between theoretical prediction (and more recent direct visualization in DNA) of large coil deformations, and prior measurements of coil size using light scattering.Broader Impacts :Viscoelastic phenomena in polymer and surfactant solutions have profound consequences in many complex flows of practical significance, including drag reduction in turbulent pipeline flow and enhanced oil recovery processes that utilize polymer and/or surfactant solutions. Understanding complex fluid rheology in both shear and, especially, extensional flows is a prerequisite to understand the more complex flows that arise in these and other technologies. As a result, the direct measurements of microscopic fluid structure in planar extensional flow proposed here have tremendous potential to positively impact technologies important to society. In addition, this project will have broad impact in scientific infrastructure and human resource development. The PI has extensive experience in the development of novel instrumentation for x-ray scattering studies of polymers under flow, drawing upon his active participation in the DND-CAT research facility at APS. More importantly, he also has a track record of making this instrumentation available to scientific collaborators, as well as to the community of synchrotron users who access APS facilities through "general user" proposals. In a similar way, the instrument developed in this project will be made available to the broader research community, expanding the benefit of this project in both the research to be performed, as well as the training of graduate students and postdoctoral researchers.