EAGER: Rheo-NMR measurement of spatiotemporal dynamics in shear banding wormlike micelle solutions

研究发现，在一类流体，如表面活性剂和聚合物的加工过程中，施加的剪切力会导致溶液中的不均匀，这种现象称为剪切诱导带状。这是一项开发准确而优雅的实验来理解这一过程的建议，影响了几个行业的当前实践，并有可能为此类材料设计更好的制造技术。对制造业有影响的研究针对的是一个被确定为国家需要的领域。目前，大分子软材料的带化理论正在研究中，但世界上很少有实验室有能力进行实验，以确定这一现象背后的基本机制。PI的实验室就是其中之一，她正在提议开发一种分子水平的实验技术来动态观察剪切带。建议提供实验时空速度和微观结构数据，以检验现有理论，并指导未来与时间相关条件下类温暖胶束溶液(WLMS)中剪切带动力学相关的建模工作。具体目标包括：(1)使用快速Rheo-核磁共振速度成像来检测WLMS中的剪切带，以验证先前理论提出的大学标准；(2)使用快速Rheo-NMR速度成像和流动补偿脉冲梯度自旋回波(PGSE)核磁共振，测量并量化与瞬时应力响应相关的速度波动的时间和长度尺度；以及(3)通过2H谱测量与剪切带和速度波动相关的WLM溶液的分子水平有序性。流变性核磁共振技术是非侵入性、非破坏性的，提供从宏观到微观的信息，有助于深入了解启动条件下剪切带的形成和振荡流动，以及流场、微观结构和瞬时应力之间的耦合。这项拟议的工作将对聚合物、表面活性剂、化工和食品行业产生影响，在这些行业，材料性能和复杂流体的控制非常重要。建议研究生和本科生参与，以及面向蒙大拿州URM学生的外展活动。

It has been found that during the processing of a class of fluids, e.g., surfactants and polymers, the applied shear can lead to non-homogeneities in the solution, a phenomenon called shear-induced banding. This is a proposal to develop accurate and elegant experiments to understand this process, impacting current practice in several industries and potentially allowing the design of better manufacturing techniques for such materials. Research with impact in manufacturing addresses an area identified as an area of National need. The banding of macromolecular soft materials is currently under investigation theoretically, but there are very few laboratories in the world that have the capability to conduct the experiments that will determine the fundamental mechanism behind this phenomenon. The PI's laboratory is one of these, and she is proposing to develop a molecular level experimental technique to dynamically observe shear banding. It is proposed to provide experimental spatiotemporal velocity and microstructure data in order to test existing theory and inform future modeling efforts relevant to the dynamics of shear banding in warmlike micelle solutions (WLMs) under time dependent conditions. Specific objectives include: (1) detect shear banding in WLMs using rapid Rheo-NMR velocity imaging to test the university criteria proposed by prior theories, (2) measure and quantify time and lengthscales of velocity fluctuation, as correlated with transient stress responses, using rapid Rheo-NMR velocity imaging and flow compensated pulsed gradient spin echo (PGSE) NMR, and (3) measure molecular level ordering for WLM solutions via 2H spectroscopy as correlated with shear banding and velocity fluctuation. Rheo-NMR techniques are non-invasive, non-destructive and offer information ranging from the macroscopic to the microscopic, providing insight into the formation of shear bands under start-up conditions and oscillatory flow as well as the coupling between the flow field, microstructure and transient stress. The proposed work will have an impact on the polymer, surfactant, chemical and food industry, where control of material properties and of complex fluids is important. Graduate and undergraduate student participation is proposed, as well as outreach activities to URM students across Montana.