AN ATTENUATED TOTAL INTERNAL REFLECTANCE SPECTROSCOPY STUDY OF E(T)(30) AT THE FREE OIL-WATER INTERFACE

Visible attenuated total internal reflectance (ATR) spectroscopy has been used to measure the mean solvent microenvironment at free ''oil''-water interfaces using the solvatochromic and acid-base properties of 2,6-diphenyl-4(2,4,6-triphenyl-1-pyridino) phenoxide (E(T)(30)). From the wavelength maximum of the solvatochromic visible absorption band of E(T)(30), the effective interfacial dielectric constants of a range of oil-water interfaces have been determined to be approximate to 8. Titration of the interfacially located probe from high to low pH leads to the creation of a positive electrostatic surface potential which can be largely accounted for using simple Gouy-Chapman theory. Complete agreement, however, is not obtained due to the non-ideal behaviour of E(T)(30) at the interface as the pH of the bulk aqueous phase is lowered. The relevance of the results obtained to solvent extraction processes are discussed.