INTERFACES IN BLOCK COPOLYMER/HOMOPOLYMER MIXTURES FORMING DRY BRUSHES

We have studied the morphology and spatial segmental distribution of constituent polymers in binary mixtures of homopolystyrene, either protonated (HS) or deuterated (DS), and polystyrene-block-polyisoprene (SI) by small-angle X-ray scattering (SAXS) and neutron scattering (SANS). The SI used has a symmetric composition and satisfies a ''dry brush'' criterion against HS or DS. The molecular weights of HS and DS are both similar to that of the polystyrene block (PS) in SI. The results show that the added homopolymer is solubilized in the PS microdomains, and the polyisoprene lamellae have a thickness independent of the volume fraction of the homopolymer, but the undulation of their interface increases with homopolymer content, These findings imply that the homopolymer is localized in the middle of the PS microdomains. The SANS analysis confirmed this implication and yielded further information on the penetration depth of 11 +/- 1 nm between the DS chains and the PS brush.