Convection-Induced Patterns in Phase-Separating Polymeric Fluids

The process of pattern formation and droplet coarsening has been studied for ternary polymeric fluids in which phase separation was induced by solvent evaporation. For a particular range of solvent evaporation rates and thicknesses of liquid layers, ordered hexagonal patterns were formed at the liquid film-air interface. We ascribe this effect to Bénard-Marangoni convection induced by solvent evaporation and estimate conditions generating periodic two-phase structures in polymeric films. Droplet coarsening rate featured a crossover from $R\sim t^{0.89}$ to $R\sim t^{0.67}$ coinciding with the onset of convection and was explained by convection-induced stabilization of droplets against coalescence.