The elastic Landau–Levich problem

We study the classical Landau-Levich dip-coating problem in the case where the interface has significant elasticity. One aim of this work is to unravel the effect of surface-adsorbed hydrophobic particles on Landau-Levich flow. Motivated by recent findings (Vella, Aussillous & Mahadevan, Europhys. Lett., vol. 68, 2004, pp. 212-218) that a jammed monolayer of adsorbed particles on a fluid interface makes it respond akin to an elastic solid, we use the Helfrich elasticity model to study the effect of interfacial elasticity on Landau-Levich flow. We define an elasticity number, El, which represents the relative strength of viscous forces to elasticity. The main assumptions of the theory are that El be small, and that surface tension effects are negligible. The shape of the free surface is formulated as a nonlinear boundary value problem: we develop the solution as an asymptotic expansion in the small parameter El(1/7) and use the method of matched asymptotic expansions to determine the film thickness as a function of El. The solution to the shape of the static meniscus is not as straightforward as in the classical Landau-Levich problem, as evaluation of higher-order effects is necessary in order to close the problem. A remarkable aspect of the problem is the occurrence of multiple solutions, and five of these are found numerically. In any event, the film thickness varies as El(4/7) in qualitative agreement with the experiments of Ouriemi & Homsy (Phys. Fluids, 2013, in press).