SWELLING EFFECTS IN SEMIDILUTE BLOCK-COPOLYMER SOLUTIONS

Small-angle neutron scattering is used to investigate swelling effects in disordered block copolymer solutions in the semidilute regime. Results are compared with Leibler's mean-field analysis for incompressible copolymer melts rescaled by Olvera to account for chain swelling. Semidilute solutions of two copolymers in toluene are considered: poly(styrene-b-methyl methacrylate) and poly(methyl methacrylate-b-methyl methacrylate-d(8)). The copolymers are found to exhibit the predicted scaling behavior for the characteristic crossover distance (or blob size) as a function of copolymer concentration, phi. However, the shift in the position of the scattering maximum, q*, is seen to have a weaker dependence on concentration than that predicted theoretically. For both systems investigated the peak position scales approximately with concentration as q*similar to phi(0.05).