CUBIC EQUATIONS OF STATE FOR ADSORPTION LAYER - ALKYLTHIOPOLYOXYETHYLENE GLYCOLS

The van der Waals, Redlich-Kwong, Peng-Robinson and an equation of sta te derived by Smith were applied to approximate the run of surface pre ssure (PI) - area (sigma) curves of the adsorption layer of n-pentyl t o n-octyl thioethers of tri- and tetraoxyethylene glycols. The equatio n parameters: excluded molar area (sigma(oi)) and an interaction energ y term (a(i)) were determined by simplex method for PI values in the r ange of 2-23.5 mN/m. The equations parameters were found to be related to the structure of the amphiphile. The sigma(oi) decreased with the length of hydrocarbon thioether chain and was nearly uniform for equat ions of state in question except for Smith equation. The value of a(i) was dependent on the amphiphile structure. It was used to obtain the interaction energy (epsilon(i)) between amphiphiles in the adsorption layer. The values of epsilon(i) determined as an increment per methyle ne group was in the range of ca. 0.2-0.32 R T, depending on the equa tion of state used.