Fddd network phase in ABA triblock copolymer melts

Abstract

Using self-consistent field theory, we investigate the stability of the orthorhombic Fddd network phase (O70) in ABA triblock copolymer melt systems. Consistent with previous findings, we observe that the gross topology of phase behavior is unchanged with varying chain asymmetry. However, the mean field critical point is displaced from the diblock copolymer value of fA = 0.5 (fA is the A segment volume fraction) to larger values as the triblock copolymer symmetry is broken with unequal A block lengths. This deviation significantly shifts the order-order phase boundaries, resulting in an appreciable region of O70 stability in the phase diagram of asymmetric ABA triblock copolymers. More importantly, the stability of the O70 phase extends to the intermediate segregation regime for select chain asymmetries. Both features are desirable for achieving a synthetic realization of the phase in binary AB block copolymer systems. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016