INVESTIGATION OF THE MICROPOLARITIES IN REVERSE MICELLES OF TRITON X-100 IN MIXED-SOLVENTS OF BENZENE AND N-HEXANE

The micropolarities in Triton X-100 reverse micelles were investigated in the mixed solvent of 30% (v/v) benzene and 70% (v/v) n-hexane, by the use of methyl orange (MO) and 1-methyl-8-oxyquinolinium betaine (QB) as absorption probes. Information about the distribution of the probe, water, and solvent molecules in the aggregates was obtained. MO is located in the polar core of the reverse micelles, but is not solubilized in the water pools, whereas QB transfers from the polar cores into the water pools when the latter are formed. In dry solutions, solubilized MO exists in two spectrophotometrically distinguishable states. The slow equilibrium between the two states is reversibly photosensitive. The population of the photostationary state is essentially eliminated by the exclusion of light or by the addition of water or electrolytes. In the mixed solvent, the micropolarity of the polar cores of dry reverse micelles increases with increasing surfactant concentration, instead of being constant as was previously found with cyclohexane as solvent. This fact is attributed to the different extents to which benzene and n-hexane can penetrate into the polar core of the aggregates. Solubilized water increases the micropolarity of the cores. In the system of 0.27 M Triton X-100 in the mixed solvent, water pool formation starts at R = [H2O]/[surfactant] = 2.5, but it begins at a smaller R value if salt (CaCl2) is present. The polarity in the water pool is, nevertheless, significantly smaller than that of bulk water.