Structure, interaction, and growth of sodium dodecyl-o-xylenesulfonate micelles in aqueous solutions

Abstract

The small-angle neutron scattering (SANS) technique was used to study the structure and interaction between micellar aggregates formed from an anionic surfactant, sodium dodecyl-o-xylenesulfonate, in aqueous solutions. In the range of monomer concentrations studied, namely, from 0.25 to 5 wt %, the intermicellar interaction was significant and the nonideality effect needs to be explicitly taken into account in the data analysis. The basic structural parameters of the micelle were determined at a low concentration by a contrast variation method at finite Q (Q is the magnitude of the scattering vector). The same set of basic parameters were then used as the input to study the growth and interaction of the micelles at higher concentrations and at different temperatures. The minimum micellar aggregate near cmc is found to be spherical with an aggregation number of 30. The aggregation number increases steadily at higher concentrations and the shape of the aggregates become prolate spheroidal. The interparticle structure factor was computed by solving a primitive model two-component Coulomb fluid in a mean spherical approximation. The effective charge of the micelle extracted from SANS experiment can be interpreted as the dressed charge they discussed in their previous paper.