Evaluating Square Gradient Theory for the Correlation and Prediction of Surface Tension

The ESD EOS [Elliott, Suresh, and Dohohue, IECR 1990, 29, 1476] is incorporated into the open-source Square Gradient Theory (SGT) library published by Mejia et al. [Mejia, Müller, and Chaparro-Maldonado, J. Chem. Inf. Model. 2021, 61, 1244]. The combined formalism is evaluated for accuracy compared to experimental measurements and empirical correlation methods. Earlier evaluations of the ESD EOS have shown it to provide accuracy like other EOSs for vapor pressure, vapor–liquid, liquid–liquid, and solid–liquid equilibria where the databases covered roughly 500 compounds and 100–200 mixtures each. For surface tension, a database of measured values for roughly 1000 compounds has been applied previously and is adapted in the present work The expanded range of compounds led to roughly tripling the number of custom characterizations for polar and associating compounds with the ESD EOS. Correlations were developed to predict influence parameters from molecular structure and EOS parameters. Based on these correlations, deviations relative to experimental data for “normal, heavy, polar, and associating” compounds were 3.7%, 3.4%, 6.1%, and 8.0%, respectively. These deviations compare to 4.0%, 7.2%, 6.7%, and 10.3%, respectively, for the best empirical methods in each classification.