Journal
CHEMICAL ENGINEERING SCIENCE
Volume 274, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ces.2023.118668
Keywords
Slot coating; Yield stress; Shear thinning; Operability window; Dimensional analysis; Visco-capillary model
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Shear thinning and yield stress are important rheological properties in coating liquids. The Herschel-Bulkley constitutive equation can represent them well. Visualization of slot-coating flows was done using Carbopol polymer solutions as a model. The effect of yield stress was significant in thin coatings, while shear thinning had a remarkable impact due to heavily curved shear rate profile.
Shear thinning and yield stress are two important rheological properties in industrially relevant coating liquids, and the Herschel-Bulkley constitutive equation can represent them reasonably. We used Carbopol polymer solutions as a model Herschel-Bulkley fluid to visualize slot-coating flows. Visualization was performed using a custom-made apparatus to detect the location of contact lines. We also developed a simple model based on the viscocapillary model. The experimental results were shown through the dimensionless coating window. The effect of the yield stress was significant in weep-ing when the coating was thin. In situations where the coating is thin, the effect of shear thinning is remarkable because of the heavily curved shear rate profile. As a result, the dimensionless coating win-dow of the Herschel-Bulkley fluid bends downward to a greater extent than that of the Newtonian fluid.(c) 2023 Elsevier Ltd. All rights reserved.
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