Evaluation of Surface Composition of Surface Active Water−Alcohol Type Mixtures:  A Comparison of Semiempirical Models

Abstract

We study adsorption at planar liquid-vapor interface of surface active binary mixtures and test three well-known models for the composition of surface phase. The models were originally presented by Guggenheim. These are compared to results for model fluids from density functional theory (DFT). The model of Laaksonen and Kulmala is in best agreement with DFT calculations. Surface mole fraction of the solute component from the Guggenheim model exceeds one for a mixture with high surface activity. The failure of the Guggenheim model is also evident in our calculations for water-methanol, water-ethanol, and water-n-propanol mixtures.

New Thermodynamics for Evaluating the Surface‐phase Enrichment in the Lower Surface Tension Component

“…As A is an extensive property of the surface phase, we can define the corresponding partial molar properties for conditions of constant T, p, and g. [14,15] Thus the partial molar surface area of constituent B, A B , is defined by Equation (6):…”

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

“…There are several existing methods available for calculating surface compositions and these methods have been addressed elsewhere [11,[20][21][22]. In order to facilitate comparison and note the differences between these methods, a brief review is provided below.…”

“…A modification of Eq. (11) has been proposed by Laaksonen and Kulmala [30] by replacing surface mole fraction with surface volume fraction as shown in Eq. (12).…”

“…There are several approaches that have been proposed to determine surface composition. This includes direct experimental measurements [5][6][7][8][9][10], calculation methods employing the Gibbs adsorption isotherm, the classical thermodynamics model, the semi-empirical/empirical models, density functional theory (DFT) [11] as well as simulations using molecular dynamics [12,13]. It should be mentioned that the direct experimental measurement of surface composition is generally quite difficult and only relatively few systems have been investigated so far.…”

“…Indeed, it has been shown that the predictive models which utilize density (or volume) are generally better than the model which utilizes only surface tension information (i.e. r ¼ x s 1 r 1 þ x s 2 r 2 ) [11]. This is not entirely surprising since preferential adsorption in the surface layer is affected by the size and interactions of the molecules and these factors are associated with volumetric properties.…”