Monitoring Ternary Systems of C12E5/Water/Tetradecane via the Fluorescence of Solvatochromic Probes

Abstract

In this work ternary systems of the nonionic surfactant C12E5 (C12H25(OCH2CH2)5OH), tetradecane, and water were probed by the use of steady state and time-resolved fluorescence. Microemulsions, which were rich in oil, rich in water, and also both continuous in oil and water, were monitored via the application of solvatochromic fluorescent probes. The hydrophobic laser dye Nile Red was used to report from the side of the oil−surfactant interface, while Prodan, which is soluble in each of the constituent solvents, was used to provide a global picture. To complement these, the hydrophilic dye 4-(2-(dimethylamino)phenyl)-1-methylpyridinium iodide was used to report from the side of the water−surfactant interface. The results show the partitioning of the probes into different environments within the ternary systems as evident from the solvatochromic shift in the emission spectra, uncovering similarities between the water-rich and bicontinuous regions in terms of polarity. Estimates for the polarity of the environments in which the fluorophores are solubilized are made in terms of the ET(30) parameter scale. The time-resolved kinetics of some of the probes have been found to be viscosity dependent, which brought out similarities between the bicontinuous and oil-rich regions along with the observation of the effect of solvent relaxation in these ternary systems.