Self-consistent field theory and coarse-grained molecular dynamics simulations of pentablock copolymer melt phase behavior

This article was originally published in Molecular Systems Design & Engineering. The version of record is available at: https://doi.org/10.1039/D4ME00138A. This journal is © The Royal Society of Chemistry and IChemE 2024. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence (http://creativecommons.org/licenses/by-nc/3.0/). ; Block copolymer (BCP) self-assembly leads to nanostructured materials with diverse ordered morphologies, some of which are attractive for transport applications. Multiblock AB copolymers are of interest as they offer a larger design parameter space than diblock copolymers allowing researchers to tailor their self-assembly to achieve target morphologies. In this study, we investigate the phase behavior of symmetric AxByAzByAx and BxAyBzAyBx pentablock copolymers (pentaBCPs) where A and B monomers have the same statistical segment length. We use a combination of self-consistent field theory (SCFT) calculations and molecular dynamics (MD) simulations to link the polymer design parameters, namely the fraction of middle block volume to the volume of all blocks of same type, τ, overall volume fraction of A block, fA, and segregation strength, χN, to the equilibrium morphologies and the distributions of chain conformations in these morphologies. In the phase diagrams calculated using SCFT, we observe broader double gyroid windows and the existence of lamellar morphologies even at small values fA in contrast to what has been seen for diblock copolymers. We also see a reentrant phase sequence of double gyroid → cylinder → lamellae → cylinder → double gyroid with increasing τ at fixed fA. The chain conformations adopted in these morphologies are sampled in coarse-grained MD simulations and quantified with distributions of the chain end-to-end distance and fractions of chains whose middle (A or B) and end (A or B) blocks remain within domains of same chemistry (A or B). These analyses show that the pentaBCP chains adopt “looping”, “bridging”, and “hybrid” ...