CAREER: Thixotropic Yield Stress Fluids - Splashing, Spreading, Sticking

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PI: Ewoldt, RandyProposal Number: 1351342The proposed CAREER project is focused on understanding the splashing of drops and jets of fluids that are rheologically complex, i.e., they behave differently than Newtonian fluids such as water. The goal of the PI is to design new fluid materials with desirable properties when the fluid impacts on a solid. Important applications of this research are fighting fires and manufacturing that involves coating technologies.Intellectual Merit:While yield stress fluids are non-Newtonian fluids with very useful functionalities, thixotropic, time-dependent yield stress fluids are still not systematically understood in the way that polymer melts and solutions are. The main objective of this proposal is to cover some of this white space by understanding the detailed phenomena that occur when droplets of thixotropic yield stress fluids impact on solids. An experimental study is proposed that will analyze droplet and jet impact experiments on dry and coated surfaces as a function of yield stress, flow viscosity, thixotropic timescales, and flow history using high-speed imaging and rheological characterization of complex thixotropic behavior. The goal is to use a deeper understanding of phenomena like splash regimes, spreading dynamics, and the material deposition pattern on the substrate, in order to meet design objectives for new fluid materials to fight fires and to develop novel manufacturing technologies. Broader Impacts:In addition to fundamental knowledge on the dynamics of complex fluids, understanding the process of splashing of thixotropic fluids can lead to practical applications with significant impact on society, for example in the manufacturing of coatings and on designing new materials to be used as additives in firefighting and fire prevention. The results can also have potential impacts to inkjet printing and agricultural spraying technologies.The educational aspect of the proposal includes educational activities that aim to engage students from the high school level and above. It is proposed to develop the "Rheology Zoo", a collection of learning modules that will be developed to connect human perception to rheological properties of fluid materials. The Rheology Zoo will target engineering undergraduates and graduate students, undergraduate Art+Design students, and high school students. The proposal here will establish The Zoo and build up the outreach pieces, starting at the home-campus of the PI, and work toward a sustainable and replicable outreach effort for other universities and geographical regions. This will occur through coursework, undergraduate honors credit, high school outreach, web videos, and do-it-yourself instructions for broad dissemination.