Spectrophotometric study of metal–ligand reactions in isooctane/Brij30/water nonionic microemulsions

The complexation between Ni2+ and pyridine-2-azo-p-dimethylaniline (PADA) was studied in isooctane/polyoxyethylenglycol dodecyl ether (Brij30)/water microemulsions at 25 °C. The apparent complexation constant depends on microemulsion composition. The proposed model, which takes into account the heterogeneity of the system at the microscopic scale, allows us to determine the distribution constants of both reactants and the complexation constant at the interface. The complex is less stable in microemulsion than in water due to a more efficient hydration of the nickel hexahydrate coordination complex that arises from the interaction between the polar head group of the surfactant and the interfacial water.