Regulating the Phase Behavior of (AB) ₃ Star Copolymer via the Intramolecular Polydispersity of A-Blocks

The self-assembly of (AB)n star block copolymers has been well studied, which is rather similar to that of a simple AB-diblock copolymer except for the slight deflection of the phase boundaries toward a small volume fraction of outer A-blocks (f). Here, we investigate the self-assembly of the (AB)3 copolymer with unequal outer A-blocks using self-consistent field theory (SCFT), focusing on the effect of intramolecular polydispersity of A-blocks (iĐA) on the self-assembly behavior. Our results demonstrate that the degree of deflection of the phase boundaries changes nonmonotonically with increasing iĐA, leading to large and complicated changes in the widths of various phase regions. Remarkably, the deflection of the phase boundaries toward small f at iĐA = 1 is reversed, shifting toward large f at a certain value of iĐA. It is revealed that the underlying mechanisms associated with the unequal A-blocks are the dissolution effect of short A-blocks and the core–shell distribution of the long and short A-blocks. Besides the deflection of phase boundaries, the two mechanisms also lead to other intriguing phase behaviors, like stabilizing the Frank–Kasper σ phase, HCP A-spheres, FCC B-spheres, and O70 B-networks.