Perpendicular lamellar-in-lamellar and other planar morphologies in A-b-(B-b-A)2-b-C and (B-b-A)2-b-C ternary multiblock copolymer melts

Ordered planar morphologies in A-b-(B-b-A)2-b-C and (B-b-A)2-b-C terpolymer melts are studied within the framework of the self-consistent field theory for volume fractions of components A, B, and C in the ratio 1:1:2 and the Flory-Huggins interaction parameters satisfying χAB = 2χAC. The stable phases turn out to be the disordered, hexagonal, parallel lamellar-in-lamellar L‖ (including the simple lamellar) as well as non-shifted and shifted (L┴ and SL┴) perpendicular lamellar-in-lamellar morphologies. Depending on the value of the ratio r = ΘAB/ΘBC, where Θ is a characteristic temperature of the units involved, different sequences of phase transitions are shown to occur. The hexagonal phase is characteristic for r≈1. The L┴ and SL┴ morphologies occur at weak and intermediate segregations whereas the L‖ morphology appears for stronger degrees of segregation. For (B-b-A)2-b-C a reduction in r favors the shifted SL┴ phase over the non-shifted L┴ one, whereas for A-b-(B-b-A)2-b-C we find re-entrant phase transitions SL┴ − L┴. The physics determining the particular phase behavior is discussed.