Shear thickening under high shear using bimodal dispersions

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Semiconductor manufacturing is an essential technology for US competitiveness in the global economy, especially as chip shortages continue to make headlines worldwide. Chemical Mechanical Polishing (CMP) is a critical processing technology that is used by the semiconductor industry to manufacture a wide variety of materials and devices, including wafers, logic devices, memory chips, and microelectronic machines (MEMs). The CMP process uses concentrated suspensions of stable particles that create abrasion and remove waste materials when polishing surfaces at very high shear rates. High shear processing is also critical in other manufacturing operations such as coating, spraying, and lubrication flows. Previous research in high shear rheology (10,000 s-1) has helped explain the underlying mechanisms leading to large increases in the viscosity of concentrated suspensions, which is commonly called shear thickening. This project will use a series of experiments to characterize the shear thickening behaviors of suspensions composed of mixtures of relatively small and large particles under a wide range of high shear conditions. Finding the mechanisms by which smaller and larger particles interact to modify and, in some cases, eliminate shear thickening under high shear conditions is an important, fundamental particle science problem. The goal of this project is to determine mechanisms underlying the dynamics of particle mixtures under flow in sufficient detail that findings can be generalized to other particle systems and flow types, including polishing, pipe, and nozzle flows. Using high shear rheology combined with scattering experiments to monitor structure formation in the suspension, the project has potential to demonstrate a new mechanism for high shear particle flow that can result in jamming of pipes and nozzles and the formation of defects in polishing. Ultimately, this research has potential to impact a wide range of industries, including large area silicon manufacturing for flat panel displays and solar cells, uniform application of paper filler and coatings, improved processing of soldering inks, ceramics, composites, and stabilization of time-release pharmaceutical formulations. The project will form the basis for training graduate and undergraduate students in the fields of rheology as well as particle and surface science. The project will also provide opportunities for middle and high school teachers to gain hands-on laboratory experience and to translate research to their classrooms.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.