Dynamical wetting transition on a chemically striped incline

Abstract

We study the dynamics of moving contact lines and film deposition on a chemically heterogeneous plate withdrawn from a liquid bath. The plate is patterned with vertical stripes characterized by alternating wettabilities. It is assumed that the interfacial slope with respect to the plate is small such that lubrication theory can be employed. The finite element method is used to solve the two-dimensional unsteady lubrication equation, which is coupled with the precursor film model and disjoining pressure to realize moving contact lines with finite contact angles. At low withdrawal velocity, a three-dimensional stable meniscus is formed. If the velocity exceeds a threshold, liquid films and droplets are produced on the more wettable stripes. When the width of the more wettable stripes is small, the contact line always loses its stability at the center of these stripes. For a sufficiently large width of the more wettable stripes, a trapezoidal film can be observed, in analogy to the wetting transition on a homogeneous plate of finite width; however, the onset of meniscus instability is found to occur at a location whose distance to the stripe boundary is independent of the stripe width, corresponding to a three-dimensional mechanism of wetting transition. Furthermore, the dynamic evolution of the liquid film is also analyzed.