Polymer Dimensions in Good Solvents: Crossover from Semidilute to Concentrated Solutions

摘要

Using small-angle neutron scattering, we studied the variation of the polymer radius of gyration (R_g) as a function of polymer concentration (φ) for solutions of a flexible-chain poly(methyl methacrylate) in chloroform. We observed for the first time a distinct crossover between swollen coils in the semidilute regime, where R~2_g ∝ φ-026±0.03) and unperturbed coils in the concentrated regime, where R_g is independent on concentration. The crossover occurs at φ~(≠) ≈ 0.15, a value that agrees reasonably well with φ~(≠) ≈ 0.21 ± 0.035, estimated with a scaling relationship between φ~(≠) and the coil overlap concentration φ*.