Morphology evolution in a diblock copolymer film.

Morphologies of surface micelles of the diblock copolymer polystyrene-block-poly(4-vinylpyridine) (PS-P4VP) at different concentrations were investigated using TEM. Highly-ordered spherical micelles were observed. The morphology was found to depend strongly on the solution concentration. A transformation from spherical to cylindrical micelles and the formation of multilayers of micelles were observed when the concentration was increased. The evolution of the morphology of the diblock copolymer film cast on Si substrates in the presence of different solvents was also investigated using AFM. We find that there is a discrepancy in the structure obtained using TEM and AFM because of the presence of a selective solvent in the TEM sample. The transformation from cylindrical to spherical micelles was observed for the film prepared under a nitrogen atmosphere. Hexagonally ordered holes were observed in the film prepared in air. The presence of moisture in the air may play an important role in the formation of this structure.