The excess thermodynamic quantities of adsorption of a binary nonionic surfactant mixture

The thermodynamic relations were developed for examining the miscibility of surfactants in the adsorbed film from the viewpoints of the thermodynamic quantities of adsorption such as Gibbs free energy, entropy, volume, enthal py, and energy. The deviation from the additivity relation, the straight li ne connecting the thermodynamic quantities of the respective pure surfactan ts as a function of the composition of the adsorbed film, was proved to yie ld the corresponding excess quantities of adsorption. The criterion of the ideal mixing was offered and summarized with respect to the composition of adsorbed film, the mean area occupied by surfactants, and the thermodynamic quantities of adsorption. The resulting equations were applied to the simp le nonionic surfactants mixture of decyl methyl sulfoxide (DeMS) and octyl methyl sulfoxide (OMS). The surface tension of the aqueous solution was mea sured as a function of not only the total molality and mole fraction of sur factants but also temperature under atmospheric pressure. (C) 1999 Academic Press.