Microphase domains of poly(styrene-block-ethylene/butylene-block-styrene) triblock copolymers studied by atomic force microscopy

Atomic force microscopy has been successfully used to observe morphologies and characterize polymer components of poly(styrene-block-ethylene/butylene-block-styrene) (SEBS) triblock copolymer surfaces. The surfaces exhibited characteristic topographies consisting of hills and valleys. The height difference between them increased with the polystyrene component, which is probably due to the stress increase between two phases. The surface area fraction of the hills also increased with polystyrene component, and the local stiffness of the hills was higher than that of the valleys. These results indicate that the hills correspond to polystyrene and the valleys to rubbery poly(ethylene/butylene). The morphology of polystyrene changed from long worm-like to mesh-like structures with increasing polystyrene content in the block copolymers and exhibited a moniliform-like structure with a periodicity of 20–30 nm. These structures may be caused by surface segregation of the polystyrene component in the block copolymer surface.