Topological Effect on the Lifshitz point of Block Copolymer/Homopolymer Blends

The effect of chain architecture on the phase behaviour of polymeric blends composed of AB-type block copolymers with identical block compositions but distinct topologies (ABA and BAB triblocks) mixed with A homopolymers is studied. The homologous ABA and BAB triblocks are obtained by linking two identical AB diblock chains through their free B or A ends, respectively. Using random- phase approximation (RPA), we show that the nature of the Lifshitz point depends on the topology of the block copolymers, exhibiting a "second-order transition" and "first-order transition" behaviours in ABA/A and BAB/A blends, respectively. Furthermore, the Lifshitz point occurs at a much lower homopolymer concentration in BAB/A blends, indicating a poorer miscibility of A homopolymers in BAB triblocks than in ABA triblocks. The difference in miscibility between these two homologous blends is confirmed by self-consistent field theory (SCFT). Our results reveal that chain topology can greatly affects the self-assembly of block copolymer/homopolymer blends.