Small-angle neutron-scattering study of micellar structure and interparticle interactions in Triton X-100 solutions

Abstract

Extensive measurements of small-angle nuetron-scattering cross sections from the nonionic micellar solutions of Triton X-100 in ${\mathrm{D}}_{2}$O are reported. An analysis of data at ambient temperature shows that the micelles are oblate ellipsoids of revolution with an axial ratio around two even at a concentration as low as 1% Triton X-100, and that there are about 20 molecules of ${\mathrm{D}}_{2}$O per surfactant molecule in the hydrophilic region. This micellar model---without invoking any further growth---is shown to explain the data for a wide range of concentrations at ambient temperature. Information about intermicellar interactions is obtained by analyzing the data using Baxter's sticky hard-sphere model, which assumes a square-well attractive potential between the micelles. This model is found to provide a qualitative interpretation of the temperature dependence of the data. However, important differences are noted for low momentum transfers. Some drawbacks of the model for characterizing the entire set of scattering data are brought out and discussed.