The use of Nile Red to monitor the aggregation behavior in ternary surfactant–water–organic solvent systems

Ternary systems of surfactants, water and organic solvents were studied by monitoring the steady-state fluorescence of the versatile solvatochromic probe Nile Red. We found not only that Nile Red can be used throughout the whole isotropic regions in the phase diagram, but also that subtle changes in the aggregation state of the surfactant can be monitored. The formation of inverted micelles in n-hexane could be followed upon the addition of small amounts of water, in addition to the formation of normal micelles in water and water–organic solvent mixtures. In aqueous C12EO4 solutions the temperature-dependent micelle-to-vesicle-to-inverted micelle transition was visualized by Nile Red fluorescence. Finally, the incorporation of solvent into the micellar interior could also be monitored using Nile Red as the probe.