Theory and Simulation Studies of the Self-Assembly of Pentablock Copolymer Melts

We study melts of linear ABABA and BABAB pentablock copolymers (pentaBCPs) using a combination of Self-Consistent Field Theory (SCFT), Coarse-Grained (CG) Molecular Dynamics (MD) and RAPSIDY to create morphological phase diagrams and identify regions of phase space that exhibit networked and highly curved morphologies that are useful for a variety of applications. First, for conformationally symmetric BABAB pentaBCPs we access the unique orthorhombic Fddd O⁷⁰ network phase at a low A block volume fraction (f_A ~ 0.18), achieved when the volume of the middle B block is 10% of the total volume of B blocks. This observation is partially confirmed by coarse-grained (CG) molecular (MD) simulations of the B_xA_yB_zA_yB_x pentaBCPs exhibiting O⁷⁰-like networks or perforated lamellae at those pentaBCP designs. SCFT free energy analysis attributes the stable Fddd phase to a reduction in packing frustration relative to the double gyroid phase. We also examine the effect of conformational asymmetry of A and B segments on the pentaBCPs phase diagram and chain conformations. We find that increasing conformational asymmetry shifts the order-order transition (OOT) boundaries shift to higher values of f_A, stabilizing highly curved phases like hexagonally packed cylinders.