Coating bead flows and operability windows of concentrated suspensions in slot coating processes considering shear-induced migration

The impact of shear-induced particle migration on coating bead dynamics and operability windows in single-layer slot coating processes involving concentrated suspensions was investigated using two-dimensional computational fluid dynamics simulations. The suspensions were modeled as Newtonian fluids containing dispersed noncolloidal, non-Brownian spherical particles, and a continuum-based diffusive flux model was incorporated to capture variations in particle concentration. The numerical methods were validated against semi-analytic and experimental data from the literature for planar channel flows. Results showed that inhomogeneous particle distributions significantly affect coating bead dynamics by reducing viscosity level in the upstream die region and lowering pressure in the feed region, which causes variations in the upstream meniscus position. Consequently, the defect-free coating regime, such as those avoiding leaking and bead break-up, was narrower in flow rate versus substrate speed plots. These findings highlight the critical role of particle concentration inhomogeneities in optimizing slot coating processes.