Dip-coating with a particulate suspension

Abstract

The coating of a plate withdrawn from a bath of a suspension of non-Brownian, monodisperse and neutrally buoyant spherical particles suspended in a Newtonian liquid has been studied. Using laser profilometry, particle tracking and local sample weighing we have quantified the thickness $h$ and the particle content of the film for various particle diameters $d$ and volume fractions ($0.10\leqslant \unicode[STIX]{x1D719}\leqslant 0.50$). Three coating regimes have been observed as the withdrawal velocity is increased: (i) no particle entrainment ($h\lesssim d$), (ii) a monolayer of particles ($h\sim d$), and (iii) a thick film ($h\gtrsim d$), where the suspension behaves as an effective viscous fluid following the Landau–Levich–Derjaguin law. We discuss the boundaries between these regimes, as well as the evolution of the liquid and solid content of the coating over the whole range of withdrawal capillary number and volume fractions.