Landau–Levich menisci

As shown by Landau, Levich and Derjaguin, a plate withdrawn out of a wetting bath at low capillary numbers deforms the very top of the liquid reservoir. At this place, a dynamic meniscus forms, whose shape and curvature select the thickness of the film entrained by the plate. In this paper, we measure accurately the thickness of the entrained film by reflectometry, and characterize the dynamic meniscus, which is found to decay exponentially towards the film. We show how this shape is modified when reversing the motion: as a plate penetrates the bath, the dynamic meniscus can “buckle” and present a stationary wavy profile, which we discuss.

In this paper, we present an original experiment of reflectometry, which allows us to measure accurately the profile of the entrained film when a plate is either withdrawn or pushed into a pool of wetting liquid. A theory is also developped.Figure optionsDownload high-quality image (38 K)Download as PowerPoint slideResearch Highlights
► This article is the first experimental study on the dynamic menisci observed in dip-coating. Discussions about the theoretical shape of the dynamic meniscus in the entrainment case or in the immersion case can indeed be found in the literature (Landau–Levich and Bretherton, respectively). There were however no careful experiments on this question, and we found it useful to probe these shapes.
► In addition, we specify in the immersion case, what is the validity of the Bretherton solution, and make the connection with the Jones–Wilson ripples, which were themselves very little discussed in the literature.
► In the withdrawing case, we determine the validity domain of the Landau–Levich solution and provide data in the regime where gravity modifies the entrainment law.