Abstract
The degree of aggregation of some commercial polyoxyethylene sorbitan fatty acid esters (Tweens) and sorbitan fatty acid esters (Spans) in cyclohexane, carbon tetrachloride and chloroform has been investigated by light-scattering, vapour pressure osmometry and sedimentation velocity techniques. Light-scattering results were corrected for the contribution of fluorescence to the scattered light, which was appreciable at excitation wavelengths of 436 nm. Mean aggregation numbers of 26 and 12 monomers were determined for sorbitan monooleate (Span 80) in cyclohexane and carbon tetrachloride respectively. No significant aggregation of this compound was observed in chloroform. Other detergents studied showed only limited aggregation, if any, in these solvents. Correlation of the aggregation numbers of Span 80 with the solubility parameters, δ, of the solvents (including results from a previous investigation) indicated that the degree of aggregation approached a minimum value when the δ values of the solute and solvent were matched.
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