Coating of a textured solid

Abstract

We discuss how a solid textured with well-defined micropillars entrains a film when extracted out of a bath of wetting liquid. At low withdrawal velocity V , it is shown experimentally that the film exactly fills the gap between the pillars; its thickness h d is independent of V and corresponds to the pillar height h p . At larger velocity, h d slowly increases with V and tends towards the Landau–Levich–Derjaguin (LLD) thickness h LLD observed on a flat solid. We model the entrainment by adapting the LLD theory to a double layer consisting of liquid trapped inside the texture and covered by a free film. This model allows us to understand quantitatively our different observations and to predict the transition between h p and h LLD .