Density, viscosity and self-diffusion coefficient of ethylene glycol oligomers conforming PEG200 with AUA4 force field

Polyethylene glycol 200 (PEG200) has emerged as a promising “green solvent” for a wide range of industrial applications, from carbon capture to pharmaceutical formulations. Despite its importance, accurately predicting its transport properties using molecular simulation has remained a persistent challenge. In this work, we present a comprehensive molecular dynamics study of the six principal ethylene glycol oligomers (diethylene through heptaethylene glycol) that comprise PEG200, employing the AUA4 force field. The unmodified AUA4 parameters yield excellent agreement with experimental density data across the full temperature range investigated, with deviations below 2 %. However, it initially fails to capture the complex viscous behavior of these systems. To address this limitation, we performed a targeted fine-tuning of the torsional energy barriers associated with the dihedral angle. This targeted re-parameterization ensures both structural accuracy and dynamic reliability, providing a highly effective computational tool for the design and study of PEG-based solvents. The optimized model shows excellent agreement with experimental viscosity data and provides reliable estimates of self-diffusion coefficients, with absolute average deviations below 5 % for viscosity and 11 % for diffusion across all six oligomers and temperatures studied. For self-diffusion coefficient estimation, the Yeh–Hummer correction was found to outperform conventional system-size extrapolation methods, particularly for the heavier oligomers. Further insight into molecular organization was obtained through radial and spatial distribution function analyses, enabling the identification and characterization of hydrogen bonding within the oligomeric systems. Importantly, these molecular-level improvements translate to the macroscopic scale, allowing for accurate simulation of the multicomponent PEG200 mixture. While standard force fields such as OPLS and GAFF adequately reproduce static properties like density, they exhibit severe limitations in predicting transport phenomena, often deviating by orders of magnitude for longer oligomer chains. The systematically lower average absolute deviations and robust validation across a broad temperature range indicate that AUA4 offers significantly improved predictive capability for PEG-based solvents. • AUA4 accurately predicts EG oligomers’ thermodynamic and transport properties. • Oligomer-specific dihedral modification significantly improved viscosity prediction. • Self-diffusion coefficient estimation depend on system-size effects. • Fine-tuning pure components enabled adequate PEG200 mixture viscosity estimates.