Mixed Micellization and Interfacial Properties of Nonionic Surfactants with the Phenothiazine Drug Promazine Hydrochloride at 30 °C

Abstract

In the present work, the micellization and adsorption behaviors of mixed systems containing an amphiphilic phenothiazine drug, promazine hydrochloride (PMZ) and nonionic surfactants in aqueous media at different mole fractions of nonionic surfactants (α1) were investigated at 30 °C by surface tension measurements. The critical micelle concentrations of the mixtures fall between the values of the individual components, which indicates nonideal mixing. With Tritons the interactions are repulsive at low mole fractions. At high α1 the mixing becomes almost ideal. On the basis of regular solution theory, the micellar mole fractions of surfactants (\(X_{1}^{m}\)) and interaction parameter (βm) were evaluated, while their interfacial mole fractions (\(X_{1}^{\sigma} \)) and interaction parameters at the interface (βσ) were calculated using Rosen’s model. The results indicate that the surfactant’s contribution is greater than that of the drug both at the interface and in micelles. The short and rigid hydrophobic structure of the drug resists its participation in micelle formation more than in the monolayer, leading to \(X_{1}^{m}<X_{1}^{\sigma}\). Values of the surface excess (Γmax) and minimum area per head group (Amin) indicate attractive interactions. Γmax increases and Amin decreases as the surfactant mole fraction increases.