Application of the small-angle neutron scattering technique to the study of solubilization mechanisms of organic molecules by micellar systems

Abstract

We present the possible contribution of the small-angle neutron scattering (SANS) technique to the molecular interpretation of the solubilization phenomena in simple micellar systems. We show for a few ternary micellar systems, that an appropriate analysis of SANS experimental data can provide information on modifications induced on micellar dimension, shape, number of monomer, and charge and on the partition coefficient of the additive and its localization inside the micellar aggregate. The influence of n-alcohols on the thermodynamics and on the structure of sodium dodecyl sulphate (SDS) aqueous solution has been extensively investigated, so the agreement between the results obtained in previous work and those obtained in this study allows the validity of data analysis procedure to be verified. The study of SDS and dodecyltrimethylammonium bromide (DTAB) solutions, containing alternatively five different macrocycles showed that: in the case of SDS solution different, but in all cases appreciable, amounts of solute were found to be localized in the micellar phase, while for most DTAB solutions there was evidence for their localization in the aqueous phase. By analysing the single system, it was not possible to establish whether the solute was in the “core” or in the “shell” of the aggregate, but from a comparison between the results related to the two surfactant systems and from the different molecular properties of the macrocycles it was possible to localize each of them inside the aggregate and to explain the different amounts found.