Flow and Drying Dynamics in Gravity- and Capillary-Driven Coating Processes
2017-06
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Flow and Drying Dynamics in Gravity- and Capillary-Driven Coating Processes
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2017-06
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Liquid-applied coatings are ubiquitous. Buildings, bridges, soda cans, compact discs, and newspapers make up a small fraction of everyday objects whose surfaces are enhanced by coatings. Typical processing steps for a liquid-applied coating include coating formulation, application, post-deposition flow, and solidification. This thesis focuses on the balance between the last two steps of this process and how this balance influences coating behavior and the ultimate quality of the final film. Specifically, post-deposition coating flows driven by gravity or capillarity are investigated in liquid systems that undergo evaporation-induced drying. In Chapter 2, coating defects caused by excessive gravity-driven flow (‘sag’) are studied. A novel particle tracking method is first developed to monitor sag in a model aqueous polymer system. A computational model is developed concurrently to validate the measurements made using particle tracking. This model is then used to generate a novel framework for predicting sag in liquid-applied coatings. Chapters 3–5 focus on capillary-driven flows in open microchannels. First, in Chapter 3, capillary flow dynamics of non-evaporating liquids are studied and compared against existing theoretical models. In Chapter 4, this work is extended to open microchannels fabricated using several three-dimensional (3D) printing technologies. 3D printed microchannels are found to confer unique flow dynamics to the capillary flow, including a distinct start–stop motion caused by surface roughness introduced by the 3D printing process. Finally, in Chapter 5, the influence of drying on capillary flow dynamics is investigated, again using a model aqueous polymer coating system. Drying is found to permanently pin the advancing contact line partway down the channel; three mechanisms of pinning are identified and characterized. Post-pinning flows induced by the coffee ring effect are found to lead to highly non-uniform dry film morphologies. The influence of surfactant, drying rate, and channel width are investigated. Throughout all of this work, the goal is to better understand the balance between flow and drying to facilitate prediction and control of coating behavior during relevant coating processes. As part of this goal, case studies are conducted throughout this thesis, investigating flow and drying behavior in real systems used in commercial coating processes, including latex paints and functional inks used in the manufacture of printed electronic devices.
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University of Minnesota Ph.D. dissertation. June 2017. Major: Chemical Engineering. Advisors: Lorraine Francis, Christopher Macosko. 1 computer file (PDF); xvi, 294 pages.
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Lade, Robert. (2017). Flow and Drying Dynamics in Gravity- and Capillary-Driven Coating Processes. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/190543.
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