Synergistic behavior of sodiumdodecylsulfate and 1,2-diheptanoyl-sn- glycero-3-phosphocholine in an aqueous medium: interfacial and bulk behavior

The synergistic behavior of sodiumdodecylsulfate (SDS) and 1,2-diheptanoyl-sn-glycero-3-phosphocholine (DHPC) binary mixtures has been studied with interfacial and pyrene fluorescence(I ₁/ I ₃) intensity measurements. From the interfacial data, the interfacial parameters; the maximum surface excess (Γ_max), or the minimum area per molecule (A _min), and the surface pressure at the critical micellar concentration (π_cmc) have been evaluated. The cmc value has been used for evaluating the free energies of micellization (ΔG ^o _m). The mixed micelle formation was evaluated with the help of the Clint equation. The SDS plus DHPC mixed micelles showed negative departure from ideality indicating synergistic interactions between the unlike components. The quantitative analysis of mixed micelle, mixed monolayer and the composition of the mixed micelle was carried out with the help of regular solution approximation. The interaction parameters, β and β^σ, in the mixed micelle as well as in the mixed monolayer, respectively showed negative values indicating synergistic behavior of SDS and DHPC molecules.