Parallel versus perpendicular lamellar-within-lamellar self-assembly of A-b-(B-b-A)(n)-b-C ternary multiblock copolymer melts.

Different types of lamellar-within-lamellar structure formations in A-b-(B-b-A)(n)-b-C terpolymer melts, with a volume fraction of components A, B, and C in the ratio of 1:1:2, are analyzed in the strong segregation limit using a simple theoretical approach. We consider the lamellar, parallel lamellar-within-lamellar, and perpendicular lamellar-within-lamellar self-assembled states. The influence of the copolymer chain length N, the value of the Flory-Huggins interaction parameters chi(AB), chi(AC), and chi(BC), and the number of blocks n in the AB multiblock chain on the phase behavior is discussed. We show that in the limiting case of n >> 1, the perpendicular lamellar-within-lamellar state becomes stable when the interaction parameters satisfy the relation 0 < chi(BC) < 0.22 chi(AC).