Effect of the nature of annealing solvent on the morphology of diblock copolymer blend thin films

The morphologies and structures for the thin film of blend systems consisting of two asymmetric polystyrene-block-polybutadiene (SB) diblock copolymers induced by annealing in the vapor of different solvents, namely, cyclohexane, benzene, and heptane, which have different selectivity or preferential affinity for a certain block, were investigated by tapping mode atomic force microscopy (AFM) and transmission electron microscopy (TEM). The results revealed that even a slight preferential affinity of good solvent for one block would strongly alter the morphology of the blend thin film. An interesting structure of so-called "spheres-between-cylinders" ("sph-b-cyl") was obtained when annealing the blend thin film with a weight fraction ratio of 50/50 of the two components in the saturated vapor of cyclohexane, which is a good solvent for]:PB and a (near) E) solvent for PS at 34.5 degrees C. The influence of the kinetic factors, such as the annealing time and vapor pressure of the solvent, together with the factors of the blend composition and the film thickness, on the morphology forming in the blend thin film systems was also investigated. Blending the block copolymers together with the solvent treatments is proved to be an effective way to control the structure and morphology of the thin films.