Spontaneous formation of mesoscale polymer patterns in an evaporating bound solution

The spontaneous formation of mesoscale polymer patterns in evaporating bound solution, was investigated. Poly(methyl methacrylate) (PMMA), polystyrene (PS), and PS-b-PMMA diblock copolymers were used as nonvolatile solutes to prepare PMMA, PS, and PS-b-PMMA toluene solutions, respectively. The pattern formation was monitored in situ by optical microscopy (OM). Spherical lens and Si surfaces were separated and examined using OM and atomic force microscopy (AFM). Highly ordered gradient concentric rings of PMMA, persisting toward the sphere/Si contact center, were obtained over the surfaces of the sphere and Si except the region where the sphere was in contact with Si. It was observed that the decrease in the center-to-center distance between two adjacent rings λ _C-C facilitated the continuity of fingers connecting between neighboring rings. Result shows that the interfacial interaction between the solute and the substrate effectively mediate the pattern formation.