Block copolymer‐homopolymer blends in the disordered state: Determination of the interaction parameter using small angle neutron scattering

The aim of this study was to determine the interaction parameter x AB and its variation with temperature from the intensity scattered By pure block copolymer (A‐B) and block copolymer‐homopolymer (B) blends where A is polydeuteratedstyrene and B polybutadiene. SANS experiments on pure copolymers of low molecular weight have shown that the scattering curve exhibits a peak of intensity related to the correlation hole effect. χ AB was determined by fitting the experimental curves using Leibler's theory and the law of variation of χ AB versus temperature was established. In the case of copolymer‐homopolymer blends, the scattering spectrum is modified because of a new and additional long range correlation effect (mixing effect) which dominates in the low q range and leads to strong forward scattering. We have not found any significant variation of χ with blend composition.