Structural and Thermodynamic Properties of CnEOm Micelles and Monolayers Reproduced by a Coarse-Grained Force Field Based on a Polarizable Water Model.

Nonionic surfactants have wide applications in industries, biomedical engineering, and other fields. They exhibit complex thermodynamic and interfacial structural behaviors across various length scales. In this study, a transferable coarse-grained force field named the polarizable optimized Morse force field (p-OMFF) for poly(ethylene glycol) (PEG)-type surfactants CnEOm is developed using a Bayesian optimization approach. The accuracy of the p-OMFF in describing the thermodynamic properties of the PEG-type surfactants is evaluated by studying the transfer behaviors of C12EO6 molecules within a three-phase equilibrium system, including micellar aggregation, free dispersion in the aqueous phase, and adsorption at the decane/water interface. The predicted critical micelle concentration and monolayer pressure isotherm derived from simulated free energy and interfacial tension align well with experimental observations, showing only moderate quantitative differences. Additionally, the model accurately captures detailed interfacial structures of CnEOm surfactants with varying alkyl-chain lengths and EO-chain lengths at the gas/water interface. This coarse-grained force field can be further applied to explore more complex interfacial phenomena and multicomponent surfactant systems at the molecular level with great efficiency.