A new modified parachor model for predicting surface compositions of binary liquid mixtures. On the importance of...

Differences in composition between the surface region and the bulk region for binary liquids can occur due to preferential adsorption, and such surface enrichment can influence mass and heat transport across the interface. In order to investigate surface enrichment, reliable methods for predicting surface compositions are required. In this study, an approach based on a modified parachor model is developed in order to provide a generally more accurate prediction for the surface composition. In contrast to other predictive models, a more "realistic" surface volume representation is considered. This model is subsequently utilized to predict the surface compositions of several binary systems, involving organic-aqueous, organic-organic and aneotropic mixtures. The surface compositions obtained are compared to those directly determined from experimental measurements, if any, and to those calculated using other predictive models. The results show that the present modified parachor model provides surface composition predictions which are equal to, and in some cases are better than (particularly for aneotropic mixtures), those provided by other models. In general, the results demonstrate the usefulness of including a "real" surface volume approximation in the surface enrichment calculations.