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

Montana State University, Bozeman MT

Investigators

Abstract

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.