THERMAL CONCENTRATION FLUCTUATIONS OF BLOCK POLYMER HOMOPOLYMER MIXTURES IN THE DISORDERED STATE .1. BINARY-MIXTURES OF SI/HS

Small-angle X-ray scattering from binary mixtures of poly(styrene-block-isoprene) block copolymer (SI) and homopolystyrene (HS) in the disordered state was studied as a function of degree of polymerization (N(HS)) and the volume fraction of HS (phi-HS). The SAXS profiles were compared with the theoretical scattering profiles based on the mean-field random-phase approximation, which incorporates the effects of the asymmetry of monomer volumes and the polydispersity in molecular weights. The theoretical profiles were found to fit the experimental profiles. The best fits of the profiles gave the Flory interaction parameter chi as a function of temperature T, N(HS), and phi-HS. The value-chi was found to increase systematically with increasing 1/T and phi-HS and decreasing N(HS).