Periodic particle concentration oscillations in slot coating of concentrated suspensions with shear‐induced migration

Abstract Slot coating is commonly used for manufacturing functional films, where the spatial distribution of particles strongly influences processability and final product performance. Despite its importance, complex flow behaviors coupled with particle migration during slot coating—such as periodic oscillations of particle concentration—have not been fully elucidated. In this study, the underlying mechanism of these oscillations is investigated using two‐dimensional computational fluid dynamics simulations incorporating shear‐induced particle migration. The results demonstrate that the periodic birth–decay cycle of the feed vortex plays a critical role in sustaining the oscillatory behavior. To facilitate a better conceptual understanding of these oscillations, a practical scaling relation at the onset is proposed. Furthermore, beyond the onset, the oscillation period is found to scale proportionally with the local residence time in the feed slot exit zone within the coating bead.