Transition from Micelles to Microemulsions in Sugar-Based Surfactant Systems Probed by Fluorescence Spectroscopy and Atomic Force Microscopy

The systems investigated by fluorescence spectroscopy and atomic force microscopy were water/sucrose laurate/oil + ethanol. The oils were R (+)-limonene and isopropylmyristate. The mixing ratio (w/w) of ethanol/oil equals unity. The fluorescent probes auramine-O and 8-anilino-1-naphthalenesulfonic acid were used to determine the minimum ω′ value for the transition of reverse micelles to microemulsions in the systems based on the two oils, as well as at different surfactant contents. The fluorescence quenching of Safranine-T (3, 6-diamino-2,7-dimethyl-5 phenyl phenazinium chloride) by the inorganic ions Fe²⁺, Fe³⁺, and Cu²⁺ was studied in reverse micelles and microemulsions. The Stern-Volmer quenching constants at different water/surfactant molar ratios (ω values) were calculated from the data of the quenching process. Atomic force microscopy was used to image the systems based on the two oils for different water to surfactant molar ratios below and above the minimum ω′ value.