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Seminar | Nanoscience and Technology Division

Advanced Rheology Measurements for Anion Exchange Membranes and Shear Thickening Slurries

NST Seminar

Abstract: Rheology measures non-Newtonian behavior of polymer, colloid, and other interesting systems. More advanced measurements monitor changes in rheology while simultaneously probing or manipulating the material. Two distinct projects will be discussed.

Anion exchange membranes (AEM) facilitate ion transport in polymer electrolyte membrane fuel cells. An AEM must have a high ionic conductivity and low fuel crossover and be chemically and mechanically stable over the lifetime of a fuel cell. Mechanical breakdown due to humidity cycling is a common limitation. A custom-built humidity delivery system was developed for a rheometer to test films at a range of temperatures (30-100°C) and relative humidity conditions (0-95% RH). The humidity oven can be used with many rheometer accessories, including dynamic mechanical analysis. Using a series of block, random, and cross-linked polymers a relationship between mechanical stress and water stress has been proposed to predict durability of anion-exchange membranes in a working electrochemical device.

Chemical mechanical polishing (CMP) slurries exhibit shear thickening at very high shear rates (>10,000 s-1). During a high-shear polishing process, it was hypothesized that individual fumed silica particles (~100 nm) collide with one another to form large agglomerates (>500 nm) that cause the slurry to shear thicken. These agglomerates tend to dig into the material surface, triggering defects such as scratches or gouges during polishing (costing the semiconductor industry billions of dollars in lost production annually). Overall, the project aims to understand thickening at high shear, link rheology with particle structure, and alter slurries to eliminate thickening.

Bio: Matthew W. Liberatore is a professor in the Department of Chemical Engineering at the University of Toledo. He earned a B.S. from the University of Illinois at Chicago and M.S. and Ph.D. from the University of Illinois at Urbana-Champaign, all in chemical engineering. His current research involves the rheology of complex fluids, especially traditional and renewable energy fluids and materials, polymers, and colloids.

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