Adsorption Properties and Composition of Binary Kolliphor Mixtures at the Water–Air Interface at Different Temperatures

Abstract

The studies on the adsorption properties and composition of the adsorbed monolayer at the water–air interface of the binary Kolliphor® ELP (ELP) and Kolliphor® RH 40 (RH40) mixtures based on the measurements of the surface tension (γLV) of their aqueous solution in the temperature range from 293 to 318 K were carried out. The γLV isotherms were described by the exponential function of the second order and the Szyszkowski equation as well as predicted by Fainerman and Miller equation. The obtained γLV isotherms were analyzed using the exponential function of the second order, the Szyszkowski, Fainerman and Miller as well as independent adsorption equations. The γLV isotherms were also used for determination of the Gibbs surface excess concentration of RH40, ELP and their mixture (Γ) at the water–air interface as well as the mixed monolayer composition. Based on Γ and the constant a in the Szyszkowski equation, the standard thermodynamic functions of adsorption were considered. From the consideration dealing with the γLV isotherms obtained by us, it results, among others, that these isotherms for the non-ideal solution of macromolecular surfactants mixture can be predicted using the Fainerman and Miller equation. From this consideration, it also results that a simple method proposed by us, based on the isotherms of RH40 and ELP, allows us to predict the composition of their mixed monolayer in the whole concentration range of RH40 and ELP in the bulk phase.