(32e) Self-Consistent Field Theory and Molecular Dynamics Simulation Study of the Self-Assembly of Pentablock Copolymers

A well-known property of block copolymers (BCPs) is their propensity to undergo microphase separation into several ordered morphologies, including lamellae, hexagonally-packed cylinders, and body-centered cubic spheres, depending on the segregation strength between their component monomers and the relative size of their constituent blocks. The self-assembly behavior of diblock copolymers has seen thorough theoretical, computational, and experimental investigation, but the characteristics of BCPs with more blocks have seen less comprehensive analysis due in part to the greater number of molecular design parameters. In this work, we study the self-assembly of melts of linear, symmetric pentablock BCPs (including the sequences ABABA and BABAB), which are symmetric about the chain midpoint, with self-consistent mean-field theory (SCFT) and molecular dynamics (MD) simulation.

The predictions of equilibrium morphology made with SCFT-based calculations are far less computationally intensive than MD simulation, but they do not account for thermal fluctuations and do not describe the conformations of individual polymer chains. We first employ SCFT calculations to efficiently construct the equilibrium phase diagram of the pentablock melts with respect to several elements of chain design, including composition and the relative size of each block. We then perform MD simulations of melts of select BCP designs to compare against the SCFT predictions of morphology and to determine individual chain conformations. We compare SCFT and MD predictions of the order-disorder and order-order transitions as well as the spatial distribution of the BCP constituent blocks. We observe qualitative agreement between SCFT and MD predictions of the formation of ordered morphologies for pentablock BCP melts.