Vesicle formation in the block copolymer/ homopolymer mixture studied by scattering methods

We studied morphology and spatial segmental distribution of particular binary mixtures of poly(styrene-block-isoprene)(SI) and homopolystyren, either protonated (HS) or deuterated (DS), with small angle-X-ray scattering (SAXS) and neutron scattering (SANS). The block copolymer SI used itself had a lamellar microdomain. Molecular weights of HS and DS were identical to each other and equal also to that of polystyrene block (PS) in SI. SAXS results obtained for SI and HS mixtures show that: (1) HS is solubilized in the PS microdomains; (2) the polyisoprene lamella has the thickness independent of wHS, weight fraction of HS, but its undulation depends on wHS. These two findings, in turn, imply that the HS added is localized in the middle of the PS microdomains, i.e., in between the PS brushes emanating from the interface of SI. We further confirmed this implication by SANS with a deuterium labeling technique; the DS segments studied for the SI/DS mixture is localized in the middle of PS microdomain with the penetration depth of 10 nm between DS and PS block chains. (author)