Modeling surface tension and interface of (water+methanol), (water+ethanol), (water+1-propanol), and (water+MEG) mixtures

Two models were used to describe the surface tension and interfacial composition of (water + methanol), (water + ethanol), (water+1-propanol), and (water + monoethylene glycol) binary mixtures. The cubic plus association equation of state was applied to compute the composition and molar volume of the phases. The first model was the equality of the chemical potential of components at the interface and the bulk liquid. Four adjustable parameters of this model were determined according to the experimental surface tensions. Then the first model was used to compute the interfacial composition of methanol, ethanol, 1-propanol, and monoethylene glycol. The computed interfacial compositions of ethanol were compared with the available experimental data in the literature. It was found that the first model successfully calculated the interfacial composition of ethanol. The second model was the gradient theory of inhomogeneous interfaces. This model had two adjustable coefficients. These coefficients were regressed based on the experimental surface tensions. The interfacial composition profiles of alcohols and monoethylene glycol were determined. The percentages of the average absolute deviation were 2.59 and 1.75 for the first and the second models, respectively. The results of both models showed that 1-propanol and monoethylene glycol had the highest and lowest absorptions at the interface. However, the second model was more suitable than the first one.