Frank–Kasper Phases of Diblock Copolymer Melts Studied with the DPD Model: SCF Results

Abstract

For conformationally asymmetric diblock copolymer (DBC) melts, we proposed a model system that can be readily used in dissipative particle dynamics (DPD) simulations and performed the corresponding self-consistent field (SCF) calculations to study the stability of Frank–Kasper (FK) phases. This provides the mean-field results needed for direct comparison with the DPD simulations, without any parameter fitting, to unambiguously quantify the fluctuation/correlation effects inherently neglected by the SCF theory but important in the low-molecular-weight DBC melts forming FK phases in experiments. Our SCF calculations of the DPD model are faster and use less memory, both by at least one order of magnitude, than those of the “standard” model and give accurate results. Among the five FK (i.e., A15, C14, C15, Z, and σ) phases considered here, C14 is found to be the only stable one; its stability is due to the conformational asymmetry and, in particular, it is stabilized over other FK phases by entropy. This is the first time C14 is predicted to be stable in SCF calculations of neat DBC melts. Our SCF phase diagrams for the DPD model of conformationally asymmetric DBCs are qualitatively different from those for the “standard” model reported in the literature, which may be due to the model differences and numerical accuracy.