Random copolymers in concentrated solutions

We study concentrated solutions of ideal A-B symmetric random copolymers in non-selective good solvents by computer simulations. When the effective net A-B interaction per thermal energy in the solution (χ_eff) is larger than 2, the scattering function has a peak at a molecular weight (N) independent wave vector k* ≠ 0. We find a certain characteristic cell size l < 1/k* below which the distribution of local monomer densities within the system is flat, i.e. the probability of finding a cell with an A monomer density ρ_A is uniform over a broad range of ρ_A values. We observe solvent enrichment in cells where ρ_A ∼ ρ_B and solvent depletion in cells which are either A or B rich. The chains dynamics for all N studied (up to N = 64) are Rouse-like regardless of the value of χ_eff. When reptation dynamics are imposed, the diffusion of the center of mass decreases substantially as χ_eff increases, suggesting that long chains are quasi-frozen.