Sedimentation and Marangoni stress in slot coating flow of particle suspension

Abstract

Slot coating is a common method in the manufacturing of a wide variety of functional films. In many applications, the coating liquid is a particle suspension and the performance of the final product is directly related to the micro structure of the film. Fundamental understanding of the suspension flow enables a better control of the particle distribution on the coated layer and, consequently, on the coating process and product performance optimization. A common simplified approach to study coating flow of non-colloidal particle suspension is to consider that the particles are uniformly distributed in the coating bead and that the liquid viscosity is constant and equal to the value of the bulk concentration. However, experimental evidences have shown that shear-induced migration leads to non-uniform particle distribution. The literature presents numerical predictions on surface inactive, neutrally buoyant particle suspension flow which have shown that particle distribution in the coated layer strongly depends on the process conditions. Here, we extend the previous analyses to explore the effect of different process conditions, including the effect of particle sedimentation and Marangoni stresses caused by surface-active particles. Results show how particle distribution changes with flow conditions and particle properties, and that Marangoni stresses can change the recirculation pattern of the flow.