Side chain effect on the self-assembly of coil-comb copolymer by self-consistent field theory in two dimensions

The phase behavior of coil-comb copolymers A–(B_m+1C_m) (side chain number m = 1–5) is investigated by real-space self-consistent field theory (SCFT). Depending on the copolymer composition and architecture, eight two-dimensional ordered phases are observed, including two-color lamellae (LAM₂), three-color lamellae (LAM₃), hexagonal cylinders (HEX), core–shell hexagonal phase (CSH), hexagon outside hexagonal phase (HEX₂), two interpenetrating tetragonal phase (TET₂), lamellae with beads inside (LAM + BD), and lamellae with core–shell beads (LAM₃ + CSB). When the volume fractions are comparable, i.e., f_A ≈ f_B ≈ f_C, LAM_3 phase is found to be stable for m = 1 while the hexagonal phases (core–shell hexagonal phase CSH or hexagon outside hexagonal phase HEX₂) are stable if m > 1. The phase region of the hexagonal phases HEX, CSH or HEX₂ enlarges with increasing m. For short coil length, such as f_A = 0.1, the phase diagram is complex, especially when m = 1. For longer coil length, the lamellae become the dominant phase. The phase transition from lamellar phase to hexagonal phase is observed with the increase of the side chain length when the side chain number m is large, which is in agreement with the experimental results. Our results give a good way to tailor the phase behavior of block copolymer and are very useful to further study the hierarchical structure of the coil-comb block copolymer.