Detection of free surface composition and molecular-level structural development of styrene(S)/butadiene(B) block copolymer films during a solution-to-film process

The surface chemical structure development in solution-cast styrene(S)/butadiene(B) block copolymer films as a function of solvent evaporation time was investigated using sum frequency generation vibrational spectroscopy (SFG). The surface structure formation of the styrene(S)/butadien(B) block copolymer (30 wt% PS) films during the solution-to-film process was found to be controlled mainly by dynamic factors, such as the mobility of the PB block in solution. For SB diblock copolymers, a pure PB surface layer was formed only when the film was cast by dilute toluene solution. With increasing concentration of casting solution, PB and PS components were found to coexist on the film surface, and the morphology of the PB component on the film surface changed from cylindrical rods to spheres. For SBS triblock copolymers, a small amount of PS component existed on the surface even if the film was cast by 1.0 wt% toluene solution. In addition, PS components at the outermost layer of the film increased and the length of PB cylindrical rods on the surface decreased with increasing concentration of casting solution.