Mesoscopic patterning in evaporated polymer solutions: new experimental data and physical mechanisms.

Mesoscopically ordered patterns were obtained when polymer solutions were applied to tilted substrates and evaporated immediately under ambient conditions in a slow air current. The patterns were studied with optical, scanning electron, and atomic force microscopy. Shadowgraph visualization of the patterning was carried out, and visualization of the flow with an ink tracer was performed. Restrained and nonrestrained flows of the polymer solution gave rise to very similar patterning. The formation of the patterns on different solid substrates, including substrates wetted with silicon oil, was investigated. The concentration of the polymer solutions exerted an influence on the characteristic dimension of mesoscaled cells. A physical mechanism of the patterning is proposed. The mechanism is based on the mass transport instability occurring under the intensive evaporation of the solvent. The model satisfactorily explains the experimental findings.