Exploring ordered structures by varying symmetric interaction parameters of non-frustrated ABCBA linear pentablock terpolymers in the melt

The phase behavior of ABCBA linear pentablock terpolymers is investigated by using the 3-dimensional self-consistent field theory. In this study, phase diagrams are constructed and used to discuss how the self-assembled morphologies are influenced by the compositions and the Flory–Huggins interaction parameters (χ) among the three components by decreasing symmetric χN value (segregation strength, where N is the total degree of polymerization) from 80 to 30. In the segregation regime of χN from 80 to 50, the microstructures formed by ABCBA linear pentablock terpolymers according to the compositions of the components are very similar. In particular, diverse complex network structures (e.g. diamond, hexagonally perforated lamellae, Fddd, and gyroid) and binary crystalline phases of cylinders and spheres can be observed. This is mainly due to the fact that the two free ends of the A block in the ABCBA linear copolymer allow the macromolecules to relieve packing frustrations. However, in the intermediate system with symmetric χN < 50, the aggregation of each components becomes weaker so that behavior of the pentablock chains is similar to triblock and diblock chains. Accordingly, the diamond and hexagonally perforated lamellae tend to transfer to gyroid and Fddd observed in linear diblock and triblock cases. Moreover, by altering the composition ratio of A/C and the length of the B block, alternatively arranged A/C spheres resemble ionic and metallic crystals (e.g. NaCl, CsCl, Li3Bi, and Nb3Sn) and alternating A/C cylinders with coordination numbers of A/C (equal to 4/4, 6/3, and 4/2) can be still observed by decreasing symmetric χN to 40 in the intermediate regime.