Morphology transformation of polystyrene-block-poly(ethylene oxide) vesicle on surface

Morphology transformation of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) vesicle on solid surface induced by vapor annealing was investigated. The PS-b-PEO diblock copolymer vesicles, prepared by dissolving in a co-solvent and adding a selective solvent, were transferred to silicon wafer surface by spin cast and then incubated in three different vapors, tetrahydrofuran (THF), dioxane (DIOX), and N, N-dimethylformamide (DMF) separately. In THF or DIOX, the vesicular structures quickly fuse together into a droplet which then spreads on the surface. While in DMF vapor, vesicle-cylinder-sphere transformation is present. The vesicle morphology transformation in DMF vapor is very sensitive to water content. A small amount of water in DMF would slow down the transformation rate, and water content would affect the cylinder packing.