APPLICATION OF THE SMALL-ANGLE NEUTRON-SCATTERING TECHNIQUE TO THE STUDY OF SOLUBILIZATION MECHANISMS OF ORGANIC-MOLECULES BY MICELLAR SYSTEMS

We present the possible contribution of the small-angle neutron scatte ring (SANS) technique to the molecular interpretation of the solubiliz ation phenomena in simple micellar systems. We show for a few ternary micellar systems, that an appropriate analysis of SANS experimental da ta can provide information on modifications induced on micellar dimens ion, shape, number of monomer, and charge and on the partition coeffic ient of the additive and its localization inside the micellar aggregat e. The influence of n-alcohols on the thermodynamics and on the struct ure of sodium dodecyl sulphate (SDS) aqueous solution has been extensi vely investigated, so the agreement between the results obtained in pr evious work and those obtained in this study allows the validity of da ta analysis procedure to be verified. The study of SDS and dodecyltrim ethylammonium bromide (DTAB) solutions, containing alternatively five different macrocycles showed that: in the case of SDS solution differe nt, but in all cases appreciable, amounts of solute were found to be l ocalized in the micellar phase, while for most DTAB solutions there wa s evidence for their localization in the aqueous phase. By analysing t he 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 c omparison between the results related to the two surfactant systems an d from the different molecular properties of the macrocycles it was po ssible to localize each of them inside the aggregate and to explain th e different amounts found.