Microdomain morphology of thin ABC triblock copolymer films

We combine scanning force microscopy experiments with ex-situ swelling in d ifferent solvent vapors to investigate the microdomain structure of a thin ABC triblock copolymer film (poly(styrene-b-2-vinylpyridine-b-tert-butyl me thacrylate)). We demonstrate that short treatment in a selective vapor and subsequent drying lead to characteristic changes in the surface morphology. The use of different solvents then allows to unambiguously identify the di fferent phases present at the surface. This approach is established studyin g polymer blend and diblock copolymer copolymer thin films of known known m orphology. It is then applied to the a priori unknown morphology of the BBC triblock copolymer thin film. The results indicate a laterally microphase- separated polymer surface in agreement with recent theoretical consideratio ns, The conclusions are corroborated by XPS measurements monitoring the ave rage surface composition of the copolymer films.