Partial and complete wetting in a micro-tube

Abstract

This study investigates the flow of a thin annular film driven by an axial force in a micro-tube. Partial wetting is taken into account using the diffuse interface theory and the film dynamics is approximated by a long-wave mesoscopic model. One of the goals is to understand the transition between partial wetting and complete wetting when the driving force increases. Two scenarios, depending on the curvature, lead to complete wetting. For low curvature, complete wetting arises by ridge spreading, whereas for a sufficiently large curvature, it arises via coating of the sliding ridge. The latter regime has no equivalent for plane substrates. The transition between the two scenarios is explained as an exchange of solution branches involving a solution composed of merged ridges.