Control of mesh pattern of surface corrugation via rate of solvent evaporation in solution casting of polymer film in the presence of convection

A polygonal mesh pattern was observed on an as-cast polymer film when cast from a dilute solution on a hot plate. It was found that the pattern was ascribed to surface corrugation. In the dilute solution, a similar polygonal mesh pattern due to convection was present. A possible imprinting mechanism of the convection pattern on the as-cast polymer film as the surface corrugation was investigated by real time observation using the so-called shadowgraph technique. For this purpose poly(styrene-ran-butadiene) random copolymer was used as a solute and toluene as a solvent. Furthermore, control of the mesh size via the rate of solvent evaporation was examined. It was found that the mesh size was increased with an increase of the rate in the regime of the lower evaporation-rate (regime I) and that it was decreased tremendously with an increase of the rate in the regime of the higher evaporation-rate (regime II). These regimes can be referred to as a kinetic control regime and a temperature-gradient control regime, respectively.