Abstract
ABSTRACTThin films of asymmetric poly(styrene‐b‐4‐vinylpyridine) (PS‐b‐P4VP) block copolymers are studied by means of in situ grazing‐incidence small‐angle X‐ray scattering (GISAXS) during solvent vapor annealing in tetrahydrofuran, a solvent selective for the PS majority block of the copolymer. Upon swelling, PS‐b‐P4VP block copolymers form hexagonal arrays of spherical P4VP microdomains in a PS matrix in films 7–9 layers thick. Deswelling the films induces a transition from hexagonal to face‐centered orthorhombic (fco) symmetry, which is stable only at ∼7 layers of spherical microdomains. Dry films show co‐existing hexagonal and orthorhombic symmetries when the solvent is removed slowly, whereas instantaneous solvent removal suppresses the fco structure, resulting in films with only hexagonal structure. The in‐plane order of microdomains is significantly deteriorated in dry films independent of the solvent removal rate.Spherical block copolymer microdomains are known to undergo a transition from hexagonal to orthorhombic packing in isothermally annealed thin films when the number of sphere layers is increased from 4 to 5. In this paper, in situ GISAXS experiments reveal that a similar transition occurs during solvent vapor annealing in a selective solvent. Interestingly, the transition from hexagonal to orthorhombic packing of spheres occurs as solvent is removed from a thin block copolymer film. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 331–338
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