HORIZONTAL DRYING FRONTS DURING SOLVENT EVAPORATION FROM LATEX FILMS

Latex films cast on a substrate often dry nonuniformly, with a drying front separating fluid domains from solidified regions passing across the film. For initial film thicknesses that are smaller than the chara cteristic horizontal distance, the analysis predicts surface-tension-d riven horizontal flow. In a limit that ensures vertical homogeneity it is shown how a front Of close-packed particles forms and propagates. Imposing a maximum for the capillary pressure causes a solvent front t o recede into the film. This recession is minimal, but can markedly af fect the propagation of the particle front An overall mass balance off ers a solution for infinite capillary pressure, thereby illustrating t he mechanism for propagation of the front. The positions of the fronts are predicted for both infinite and finite domains as a function of t he maximum capillary pressure. Selective or nonuniform evaporation pro duces final film profiles, while the evaporating regions are still vis ible. After predictions otter different size areas are made, the small est area is compared with experiment.