(418e) Predicting the Surface Tension of Liquid Mixtures with or without a Supercritical Component

In order to predict how fluids behave and interact with their surroundings (e.g., contact angle), their surface tension needs to be accurately quantified. For liquid mixtures, surface tension needs to be known as a function of both composition and temperature. Previously, we developed an equation for accurately predicting the surface tension of aqueous mixtures (Langmuir 2017 33 11077–11085). Herein, we develop a new algebraic equation for predicting the surface tension of nonaqueous mixtures (with and without a supercritical component) as a function of composition and temperature. For those mixtures with a supercritical component, we use an equation of state to determine the critical composition of the mixture as an input to our model for surface tension. For our surface tension equation, we need a minimal amount of experimental data for extracting fitting parameters: (i) surface tension as a function of temperature for each pure component and (ii) surface tension as a function of composition at a single temperature for each binary mixture. We find that our model’s fitting parameters are composition- and temperature-independent. Our equation predicts surface tension within an average absolute deviation of 0.22 mN/m away from experimental data of 8 binary systems where one compound is supercritical (466 data points; temperatures between 173 and 442 K; pressures between 0.1 and 35.9 MPa) and within an average absolute deviation of 0.10 mN/m for 7 binary systems where both compounds are subcritical (293–333 K; 236 data points). We also make predictions for the ternary system methanol + ethanol + water within an average 0.71 mN/m of reported experimental data (196 data points). The simplicity and wide applicability of our surface tension equation will enable its use in various fields ranging from microfluidics to atmospheric physics, particularly those where multicomponent, multiphase systems undergo changes in temperature, pressure, or composition. This research was supported by funding from the Natural Sciences and Engineering Research Council of Canada, Alberta Innovates and Alberta Advanced Education, and the University of Alberta. JAWE holds a Canada Research Chair in Thermodynamics.