Study of core–shell structure of cesium dodecylsulfate micelles using small-angle X-ray and neutron scattering

Abstract

Small-angle X-ray and neutron scattering (SAXS and SANS) measurements were carried out to study core–shell structure of cesium dodecylsulfate (CsDS) micelles in aqueous solutions at different temperatures and surfactant concentrations and in the presence of salts. Data analysis shows that the micelles are prolate ellipsoid in shape. Assuming the semi-minor axis of the core to be equal to the fully extended length of the hydrocarbon chain, the values of semi-major axis, shell thickness, aggregation number and fractional charge on the micelle were obtained from SAXS data and compared with those obtained from SANS data. It is seen that while shell thickness is independent of surfactant concentration, the micelle size increases with increase in surfactant concentration. Micelle size and shell thickness decrease with increase in temperature. Addition of salts (sodium chloride or cesium chloride) results in growth of micelles with reduction of fractional charge on the micelle. The micelle size obtained by SANS is larger than that obtained by SAXS when CsDS solutions are prepared in H2O for SAXS experiments and in D2O for SANS experiments. However, results obtained in SAXS experiment using D2O as solvent agree remarkably with those obtained using SANS.