Slot coating flow of particle suspensions: Particle migration in shear sensitive liquids

The functionality of several coated products, such as anti-reflection films and flexible electronics, depends on the complex microstructure of the deposited liquid layer. In many of these applications, the coating liquid is a particle suspension composed by small, solid particles suspended in a viscous liquid medium. Particle suspensions are classified as non-Newtonian fluids, especially at high concentrations. The non-Newtonian behavior of the coating liquid strongly affects the inner structure of the deposited liquid layer and the operability limits of slot coating processes. In this work, we study particle migration and the low-flow limit in slot coating flows of particle suspensions. Both shear rate sensitive and non shear rate sensitive suspensions are considered, and shear-induced particle migration is described by the Diffusive Flux Model. The conservation equations are solved together with the elliptic mesh-generation method to compute the position of the free surfaces using a stabilized Finite Element Method. The results show how particle migration and the rheology of the coating liquid affect the final particle distribution on the deposited liquid film and the process limits in a typical slot coating flow.