Elucidating the Physical Basis of Entropy Scaling for Diffusion Coefficients: A Complementary Approach using Molecular Simulation, NMR Experiments, and Fluid Theory

• Applicants: Dr. Kerstin Münnemann; Professor Dr.-Ing. Simon Stephan
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 556679904

The modeling and prediction of diffusion coefficients of fluids and fluid mixtures is important for many applications. Entropy scaling (ES) has emerged as a popular and powerful tool in the past years. In very recent works of the applicants, it was extended for the modeling of diffusion coefficients of mixtures. Yet, the inner working mechanisms of ES are not well understood today. Moreover, fundamental problems remain for the ES modeling of associating fluids – the reasons for those are also not understood yet. This project aims at elucidating these questions and identifying a route for improving ES for associating fluids. This will be done in a complementary approach using molecular dynamics (MD) simulations, NMR spectroscopy, and fluid theory modeling. For elucidating the scaling mechanisms of ES and the issues of associating fluids, we will develop a method for analyzing the primary data sampled in NMR experiments (pulsed field gradient spectra) and in MD simulations (correlation functions). Both primary data types are measures for the structure and dynamics of the particles on the atomistic level and therefore suited for elucidating the relation of diffusion and entropy. The results from these primary data for both associating and non-associating fluids will be analyzed by anomaly detection for identifying peculiarities in the associating fluids.

• DFG Programme: Research Grants