Crystal Growth near Moving Contact Lines on Homogeneous and Chemically Patterned Surfaces

We have systematically investigated how solution crystallization in the proximity of moving contact lines can be modulated by the parameters of the coating flow as well as chemical patterning of the substrate surface. We have studied the monoclinic model substance nicotinamide in the solvent isopropanol, which tends to form needle-like crystals in bulk solution. Three crystallization regimes were identified dependent on the coating speed. At high speeds viscous entrainment dominates over solvent evaporation, and an essentially azimuthally isotropic, spherulithic morphology results. For intermediate speeds a branched morphology with preferential alignment parallel to the coating direction is observed. For low speeds, filament-like crystal patterns well aligned with the coating direction were obtained.