Determination of Enthalpy and Entropy of Per- and Polyfluoroalkyl Substances

Abstract Per- and polyfluoroalkyl substances (PFAS) are widely used as synthetic chemicals and are known for their persistence in the environment and potential health risks. Among them, perfluoroalkyl carboxylic acids (PFCAs) and perfluoroether carboxylic acids (PFECAs) are of particular interest due to their industrial applications and environmental impact. While the thermodynamic properties of PFCAs have been studied to some extent, data on PFECAs remain limited. In this work, a combination of a detailed statistical thermodynamics method and an electronic structure method is employed to predict key thermodynamic properties, including heat capacity, sensible enthalpy, enthalpy, and entropy of formation, for both PFCAs and PFECAs over a wide range of temperature. The isogyric reaction scheme for C/H/O/F organic compounds is used to determine enthalpy of formation. Additionally, NASA seven-coefficient polynomial parameters have been developed for heat capacity, enthalpy, and entropy, facilitating their use in computational modeling. All results for PFCAs are compared with previous studies, while PFECAs, which have been rarely explored, are systematically examined.