Polymer film deposition from a receding solution meniscus: The effect of laminar forced air convection

When the meniscus of a polymer solution with a volatile solvent recedes over a wettable substrate, a polymer layer is deposited onto it. Even for chemically homogeneous and topographically flat substrates and constant coating speeds, the layer can exhibit quasi-periodic line patterns extending parallel to the contact line of the liquid meniscus. In this manuscript, we study such unstable solution deposition processes by means of well-controlled, systematic experiments and numerical simulations. The presence of laminar forced air convection gives rise to a linear increase in the average layer thickness with air flow rate. Initially, the line patterns increase in width and height with increasing air flow rate. However, beyond a certain critical value the coating instability is suppressed.