Ordered structure in blends of block copolymers. 4. Location of the short diblock

We used small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) to examine a blend of two polystyrene-block-polyisoprene polymers with different molecular weights (6.73 x 10(4) and 1.0 x 10(4)) and volume fractions of polystyrene (0.81 and 0.52, respectively), i.e., a blend of the type (A-B)(alpha)/(A-B)(beta). The results show that the junctions of the short diblock copolymer are localized at the interface in the lamellar microdomains at low temperatures with a relatively strong segregation and that more of the short diblock copolymer is delocalized with their junctions moving away from the interface with increasing temperature. The domain spacing is seen to decrease with the addition of the short diblock to the long diblock copolymer at a given temperature. The domain spacing of blends with a large amount of the short diblock is seen to increase or stay constant with increasing temperature, which is radically different from the behavior of pure diblock copolymers or their blends with homopolymer. The SANS results indicate that the first-order scattering peak is of a much lower intensity than expected, compared with the SAXS results, or in some cases suppressed completely. For the case of the 60/40 (w/w) blend, the first-order peak is suppressed at low temperatures and appears at high temperatures, indicating delocalization of the short diblock. All of these results are consistent with the picture that the junction of the short diblock is localized at the interface but the degree of localization decreases with increasing temperature.