Elastic scattering from asymmetric, polydisperse block copolymer systems in the disordered state

Abstract

We present the scattering function for AB diblock copolymers, and their mixtures with homopolymers A and/or B, in the single-phase state. The calculation is a generalization of earlier random-phase approximation calculations to include differences in monomer volumes and statistical segment lengths, as well as homopolymer molecular-weight distributions and copolymer composition distributions. Their individual and combined effects on the scattering profiles I( q) and on the Flory interaction parameter determined from I( q) are discussed. Using poly(styrene- b-isoprene) as a specific example, we found that for pure block copolymer the asymmetry effects are negligible if the volume fraction of one of the blocks, f A, is close to 0.5, but that they become significant as f A approaches zero or unity. For a blend, we found asymmetry effects over a wide range of system characteristics.