Real-time, Acoustic Tuning of the Rheology of Shear-Thickening Suspensions

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Many fluids used in industrial processes are shear-thickening. That is, they become more viscous the faster they are forced to flow. This feature can make their use and manipulation costly, require significant energy, and damage processing equipment. This research will identify low cost and energy efficient techniques for making shear-thickening fluids less viscous so that they can be more easily and efficiently used. Experiments are aimed at showing that acoustic (ultrasound) waves can be generated in a controlled fashion to tune and reduce the viscosity of shear-thickening fluids. This viscosity reduction will result in less energy consumption in moving and processing of the fluid. The success of this work could facilitate many important manufacturing processes, including the design of self-healing materials and 3D printing applications.It has been shown that shear thickening can be controlled and mitigated by applying an orthogonal perturbation to the flow. Previous studies have largely used electrical and magnetic properties of colloidal suspensions to tune shear thickening, which is only useful for particles with these unique properties. Boundary-driven shear flows have also been studied, but are not standard in manufacturing contexts. Thus there is an urgent unmet need to demonstrate remote viscosity tuning in pressure-driven flows of shear-thickening suspensions of passive particles. What is currently unknown is how remote perturbation of pressure-driven flows at the particle level to break force chains can be implemented in a scalable architecture that can tune viscosity on macroscopic scales and thus facilitate manufacturing processes. We will de-thicken colloidal suspensions by inducing orthogonal perturbations with biaxial bulk-acoustic-wave forcing. By characterizing both the systemic response and the microscale structure of the colloidal chains, we will answer the fundamental question of how shear-induced force chains can be broken in pressure-driven flow. Remote perturbation and de-thickening of fluids is important to realizing the many exciting engineering benefits of shear-thickening fluids (self-healing materials, inkjet printing, 3D printing, etc.). These benefits cannot be achieved unless the manufacturing and processing of shear-thickening suspensions can be managed in a way that is thermodynamically and economically efficient and is minimally damaging to equipment.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.