Real-space mean-field approach to polymeric ternary systems.

Phase separated structure of ternary blends of A and B homopolymers and symmetric AB diblock copolymer is investigated using a lattice (real-space) self-consistent field theory. This paper includes the detailed description of our published results [Kodama, Komura, and Tamura, Europhys. Lett. 53, 46 (2001)] as well as more extended calculations. We consider the symmetric case, namely, (i) both A and B homopolymers have the same degree of polymerization N[sub A]=N[sub B]; (ii) AB diblock copolymer of length N[sub AB] is symmetric; (iii) average volume fractions of A and B homopolymers are equal. We looked into the influence of relative chain lengths α=N[sub A]/N[sub AB] on the phase separated structure. Our numerical simulations are performed in the real space without assuming the symmetry of the structure a priori. For the fixed copolymer length and α<1, the typical length scale of the microphase separated structure become smaller for relatively shorter homopolymer chains (small α). In other words, the homopolymers becomes more efficient to swell the microphase separated structure for longer homopolymer chains (large α). Detailed free-energy analysis revealed that the stability of the lamellar phase is marginal for small block copolymer volume fraction. For α>1, on the other hand, three-phase coexistence either between the disorder, A-rich and B-rich phases or between the lamellar, A-rich and B-rich phases is observed. [ABSTRACT FROM AUTHOR]