(299f) Hydrodynamically-Driven Assembly in Dip Coating From Particle Suspensions

Our computational study of dip coating from a particle suspension reports striped assemblies as those observed experimentally when the thickness of the withdrawn film is comparable to or smaller than the particle size. In this so-called thin-film entrainment regime, particles can assemble within the entrained film due to capillary interactions that minimize the free surface energy. Below a critical withdrawal speed, however, we find that the assembly process mainly occurs within the dynamic meniscus before particles can actually enter the thin film. This type of assembly process is observed when large interfacial forces required to deform the dynamic meniscus prevent particles from entering the film. Interfacial forces are overcome by hydrodynamic drag when a certain number of particles assemble in a close-packed formation. Hence, the assembly process within the dynamic meniscus is driven by hydrodynamic forces imposed by the background flow configuration. At low particle concentrations, the hydrodynamically-driven assembly significantly enhances the order and periodicity of the formed particle arrays.