Abstract
The solubilization behavior of a series of sodium alkyl sulfates (SAS), CnH2n+1OSO3Na (n= 12, 14, 16, 18), toward an oil-soluble dye, Oil Yellow OB (C.I. Solvent Yellow 6), has been studied in relation to the molecular weight and concentration of poly (ethylene oxide) (PEO) in theaqueous solutions of sodium sulfate (2.2 × 10-2 mol/l). The solubilization of Oil Yellow OB was determined at several temperatures (30-60±0.02°C). Excess dye was removed by filtration througha glass filter (G4) and then a filtrate was diluted with methanol. The amount of solubilized dye was determined spectrophotometrically at 442 nm.
The amount of solubilized Oil Yellow OB (S) in SAS solution became greater by the addition of PEO. S increased with an increase in the molecular weight (Mw) and concentration of PEO. The solubilizing power (S/C) corresponding to the slope of each S vs. SAS concentration (C) curve changed similarly to S. The break point (Cb) in each S vs. C curve showed an opposite tendency from S or S/C. For Mw of PEO larger than ca. 300, 000, S/C and Cb became practically constant. The absorption spectra of Oil Yellow OB in various solvents suggest that the dye is mainly solubilized in the hydrophobic parts of SAS micelles in the absence of PEO, while, in the presence of PEO, it is contained in both the hydrophobic parts and PEO regions of SAS-PEO complexes. The effect of the chain length of hydrocarbon of SAS and temperature on S/C and Cb was also discussed.
