Critical Solutal Marangoni Number Correlation for Short-Scale Convective Instabilities in Drying Poly(vinyl acetate)-Methanol Thin Films

Abstract

A new empiric correlation for the critical solutal Marangoni number as function of the Péclet and Schmidt numbers is proposed. It is based on previously published experimental flow field data in drying poly(vinyl acetate)-methanol films with an initial thickness in the range of – and an initial solvent load of to , as well as newly derived concentration profile measurements and 1D drying simulations. The analysis accounts for realistic transient material properties and describes the occurrence of short-scale convective Marangoni (in)stabilities during the entire drying process with an accuracy of 9%. In addition, the proposed correlation qualitatively follows trends known from theory. As convective Marangoni instabilities in drying polymer films may induce surface deformations, which persist in the dry film, the correlation may facilitate future process design for either thin films with uniform thickness or deliberate self-assembly.

Pattern Formation in Evaporating Polymer Solutions─Interplay between Dewetting and Decomposition

“…As an example, we often observe ring-like patterns formed by the evaporation of spilled-over suspensions like coffee, inks, or paints. − Several industrial applications like large-scale coating, , fabrication of solar cells, inkjet printing, disease detection, and forensic investigation of blood droplets rely on the understanding of such evaporation-induced patterns. Further, the evaporation of solutions containing one or more components provides an avenue to control pattern formation across several length scales. − Despite its enormous practical potential, the complex interplay of several physicochemical processes during evaporation limits our ability to fully harness evaporation to control pattern formation. ,− …”