Hierarchical structure-within-structure morphologies in A(2)-star-(B-alt-C) molecules.

We employ dissipative particle dynamics (DPD) to examine the self-assembly behavior of A(2)-star-(B-alt-C) molecules. We successfully observe various types of hierarchical structure-within-structures, such as A-formed spheres in the matrix formed by B and C alternating layers, hexagonally packed A-formed cylinders in the matrix with B and C segregated layers, B and C alternating layers-within-lamellae, coaxial B and C alternating domains within hexagonally packed BC-formed cylinders in the A-matrix, and co-centric BC-alternating domains within BC-formed spheres in the A-matrix, by increasing the A composition. Generally speaking, the small length-scale B and C segregated domains are in parallel to the large length-scale structures. This hierarchical periodicity along the same axis as well as the various characteristic structures, that the A(2)-star-(B-alt-C) copolymers display, are quite different from those in A-block-(B-graft-C) coil-comb copolymers. Moreover, it is interesting to find that when the copolymer chain length increases, though the hierarchical structure type is maintained, the number of small length-scale lamellae that can form within the large length-scale structure increases. These hierarchical structures under various compositions are reported theoretically for the first time in the copolymer systems consisting of the alternating blocks, and are in good agreement with the most recent experimental work by Matsushita and co-workers (Macromolecules 2007, 40, 4023).