PHASE-SEPARATION OF SYMMETRICAL POLYMER MIXTURES IN A COMMON GOOD SOLVENT IN THE SEMIDILUTE CONCENTRATION REGIME

Monte Carlo simulations of lattice models of binary (AB) symmetric pol ymer mixtures (chain lengths N-A = N-B = N) in a common good solvent a re carried out and the phase diagrams and critical properties of the u nmixing transitions are estimated and interpreted in terms of recent t heories. Polymers are modeled by self-avoiding walks of length N = 16, 32 and 64 on the simple cubic lattice. Data for vacancy concentration s of phi(V) = 0.6, 0.8 and 0.85 are analyzed. It is shown that for N = 16, phi(V) = 0.85 no phase separation occurs, down to the lowest temp erature, while for N = 32, phi(V) = 0.85 still phase separation occurs but no longer is complete. Our results are compatible with a scaling theory based on a ''renormalization'' of the Flory-Huggins chi-paramet er due to ''blob'' effects.