Spontaneous pattern formation based on the coffee-ring effect for organic-inorganic hybrid films prepared by dip-coating: effects of temperature during deposition

We prepared silica-poly(vinylpyrrolidone) (PVP) hybrid films via a temperature-controlled dip-coating process and investigated the influence of the coating temperature (i.e., the temperature of substrates, solutions and atmosphere) on the spontaneous pattern formation based on the coffee-ring effect. Micron-scale stripe patterns were spontaneously formed on the surface of the films at high coating temperatures over 40 degrees C during dip-coating. The stripe patterns were arranged perpendicular to the withdrawal direction, and the height and width of the patterns increased with increasing coating temperature. Such spontaneous pattern formation is attributed to the evaporation-driven capillary flow of coating solutions at the meniscus, and the stripe patterns with larger heights and widths are thought to be achieved by the capillary flow activated at higher coating temperatures.