Using the SAFT-?-Mie to Generate Coarse-Grained Force Fields Useable in Molecular Dynamics Simulations: Describing the Micellar Phases of Polyalkylglycols in Aqueous Solutions

In this work, we showcase the potential of the SAFT-gamma-Mie equation of state to obtain, in a top-down approach, coarse-grained molecular models capable of describing micelliza-tion phenomena. For this purpose, we selected polyethylene oxide (PEO)/polypropylene oxide (PPO) triblock copolymers in aqueous solutions as a case study. The model was fitted to reproduce the thermophysical properties-liquid densities and vapor pressures-of small PEO/PPO oligomers as well as the activity coefficients or liquid-liquid phase diagrams of their binary mixtures with water. At low concentrations, the MD simulations show the formation of spherical micelles of morphology comparable to experiments, with the characteristic star-shaped or flower-shaped morphology depending on the polymer block sequence. The local structure and molecular conformations were analyzed, showing distinctions between the two types of aggregates. At higher concentrations, depending on the co-polymer sequence, the molecules form larger micelles or coalesce into larger aggregates when signs of phase separation are observed, as expected.

Automated summary

In this study, the SAFT-gamma-Mie equation of state was used to develop coarse-grained molecular models for describing micellization phenomena in a top-down approach. Polyethylene oxide (PEO)/polypropylene oxide (PPO) triblock copolymers in aqueous solutions were selected as the case study. The model was successfully fitted to reproduce the thermophysical properties and liquid-liquid phase diagrams of PEO/PPO oligomers and their mixtures with water. Molecular dynamics simulations showed the formation of spherical micelles with star-shaped or flower-shaped morphology at low concentrations, and the formation of larger micelles or aggregates at higher concentrations.