SANS Study of the Structure of Sodium Alkyl Sulfate Micellar Solutions in Terms of the One-Component Macrofluid Model

Abstract

A SANS study of 0.073 c micellar solutions of sodium alkyl sulfates with chain length from nC = 9 to 16 was carried out. Micelles were assumed to be ellipsoids which may grow only in the direction of their axis of symmetry. The structure factor was calculated in terms of the one-component macrofluid model by assuming DLVO potential. The contact radius and the strength of the interaction potential were handled as free fitting parameters; the electrostatic potential and the apparent micellar charge on the contact surface were derived from the latter. The assumptions imposed on the conformation of the micellar cores are sustained by the best-fit parameters of the form-factor. For nC = 9−13 the mean aggregation numbers are in good, or at least, in acceptable agreement with the predictions of a recent thermodynamic theory of micellization. The difference found between the mean core and contact radii suggests that an unknown repulsive interaction may be present which prevents the micelles from astructurally pos...