A new equation for the surface tension of carboxylic acids

This work presents a new formula to calculate the surface tension of the important organic family of carboxylic acids. As a first step, the raw surface tension data of acids (experimental, smoothed and predicted) accepted by DIPPR database were collected. After the data analysis, only the experimental data were considered for the calculations. The selected data were regressed with a scaled equation based on three input parameters: radius of gyration, critical density and critical temperature as fluid constants. Particularly relevant is the introduction of the radius of gyration as fluid parameter, that is a noticeable difference with respect to other previous literature methods. The entire dataset was split into two groups, according to their chemical characteristics and acidity. The proposed equation was regressed for the two groups, separately. The ability of the model to predict the surface tension of new acids was tested for 5 acids for which only one datum point was present in the database and that were not considered during the regression. To check the behavior of the model also at higher reduced temperatures, 6 data for ethanoic acid were also kept for validation. The validation gave satisfactory results. The selected data also were analysed with the most reliable semi-empirical correlating methods in the literature based on the corresponding states theory. The proposed equation is very simple and gives noticeable improvement with respect to existing equations.