Indirect Evidence for Molecular Association of Polycyclic Aromatic Hydrocarbons in Aqueous Soap Solutions from Light Absorption and Fluorescence

Aqueous solutions of alkyl sulphates containing small amounts of the free alkanol differ in their dissolving properties for polycyclic aromatic hydrocarbons from aqueous solutions of the pure soap in concentrations near the CMC. The differences are observed only near the CMC of the pure soap, where the soap solutions containing free alkanol have a minimum of the surface tension. The observed alterations are deviations from the Lambert-Beer law, energy transfer, and changes of the fluorescence quantum efficiencies, when the soap concentration is varied. The different results are consistent with the assumption that microcristalline molecular van der Waals associations are brought into solution by the soap solutions which were studied