Self-assembled structures in blends of disordered and lamellar block copolymers: SAXS, SANS and TEM study

BACKGROUND: The phase behaviour of copolymers and their blends is of great interest due to the phase transitions, self-assembly and formation of ordered structures. Phenomena associated with the microdomain morphology of parent copolymers and phase behaviour in blends of deuterated block copolymers of polystyrene (PS) and poly(methyl methacrylate) (PMMA), i.e. (dPS-block-dPMMA)(1)/(dPS-block-PMMA)(2), were investigated using small-angle X-ray scattering, small-angle neutron scattering and transmission electron microscopy as a function of molecular weight, concentration of added copolymers and temperature. RESULTS: Binary blends of the diblock copolymers having different molecular weights and different original micromorphology (one copolymer was in a disordered state and the others were of lamellar phase) were prepared by a solution-cast process. The blends were found to be completely miscible on the molecular level at all compositions, if their molecular weight ratio was smaller than about 5. The domain spacing D of the blends can be scaled with M(n) by D similar to M(n)(2/3) as predicted by a previously published postulate (originally suggested and proved for blends of lamellar polystyrene-block-polyisoprene copolymers). CONCLUSIONS: The criterion for forming a single-domain morphology (molecularly mixed blend) taking into account the different solubilization of copolymer blocks has been applied to explain the changes in microdomain morphology during the self-assembling process in two copolymer blends. Evidently the criterion, suggested originally for blends of lamellar polystyrene-block-polyisoprene copolymers, can be employed to a much broader range of block copolymer blends. (C) 2008 Society of Chemical Industry