Structure Formation, Rheology and Internal Stress Dynamics in Shear Thickening Attractive Colloidal System

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CBET-0828905OsujiThis proposal outlines a 3-year plan of integrated research, teaching and outreach centered on complex fluid rheology. Much effort has been devoted to understanding the flow behavior of particulate laden fluids, with the underlying ubiquity of these materials in industry a strong motivator. The recent observation of shear thickening in gel forming colloidal systems presents an opportunity to contribute to the fundamental understanding of the rheology of this important class of materials.A. Scientific objectivesThe proposed work is directed towards answering key questions regarding the observed shear thickening, and to exploring several qualitatively new phenomena displayed by shear thickened gels. This proposal describes a detailed plan for (1) the characterization of shear thickening in these materials, (2) the study of internal stress dynamics in stationary states and (3) the study of the evolution of ordered anisotropic microstructures on shear deformation of such colloidal gels.B. Intellectual meritSignificant attention has been given to shear thickening in repulsive and hard sphere systems. By contrast, in flocculating systems, which constitute the majority of industrial applications, shear thickening has neither been predicted nor explored. The proposed study addresses this gap and will elucidate the origin of shear thickening in attractive systems as well as the dependence on interaction strength and volume fraction. It will constitute the first quantitative study of short and long timescale dynamics of stresses that result on system quenches from the liquid to the gel state in soft materials. Finally, it will provide a new look, with unparalleled detail, at the formation of anisotropic vorticity-aligned aggregates in a complex fluid under flow.C. Broader impact1. Technical impactFumed particles are commodity materials with sales measured in millions of tonnes and applications in all manner of formulations and products. The rheology of filled Newtonian and viscoelastic fluids is an active research area for exactly this reason, and scientific exchange between industry and academia is common. The PI maintains a relationship with Cabot Corp., and their personnel often attend meetings of the local complex fluids community, facilitating further interactions. There are also technical exchanges with industry concerning rheometer design and operation.2. Education and OutreachThe PI is a new faculty member with a strong interest in education and outreach. This project will actively seek the participation of underrepresented groups for three undergraduate research projects. Graduate students will gain a broad experimental background in complex fluids and be involved in education through teaching, mentorships of undergraduates and local outreach events. As part of a broader thrust in complex fluids/soft materials research at Yale, the PI will develop coursework incorporating themes from the project in a module on complex fluid rheology. Results will be published on an interactive website and will be regularly presented at the quarterly meetings of the regional New England Complex Fluids Workgroup (NECF) as well as at national meetings.