EFFECT OF ALKYLPARABENS ON THE SOLUTION STATE OF SODIUM LAURYL SULFATE MICELLE .4. GEL-FILTRATION OF SOLUBILIZED SYSTEMS

Incorporation of methyl-, ethyl-, and butylparabens into sodium lauryl sulfate (SLS) micelle was examined by measurement of ultraviolet spectra, conductance, degree of counterion binding to the micelle, and elution volume of micelles solubilizing alkylparabens. The results show that alkylparabens penetrated only a little into the palisade layer. This phenomenon was closely related to the diluted charge density of micellar surface and the decrease of micellar volume by the solubilization. The factors for stabilization of the micelle by solubilization of alkylparabens were assumed as reduction of the free energy of a micelle due to the diluted surface charge density on a micelle, the entropy of mixing of the mixed micelle, and the decrease of activity coefficient of SLS molecule in the mixed micelle, γ*m, which may be considered as geometrical factors. Among these geometrical factors the hydrophobic interaction between alkylparaben and the hydrocarbon part of SLS micelle will be of importance. © 1979.