STRUCTURE AND INTERACTION OF LITHIUM DODECYL-SULFATE MICELLES IN THE PRESENCE OF LI-SPECIFIC MACROCYCLIC CAGE - A STUDY BY SANS

We study by small-angle neutron scattering (SANS) the interaction of macrocyclic cage CESTO (C17H37N5) with lithium dodecyl sulfate micelles (LDS) in solution. At pH 12.7 the CESTO molecule in aqueous solution is neutral and can complex one Li+ ion, incorporating it into its cage. The result is the formation of a positively charged cage, and it is attracted by the negatively charged head groups of dodecyl sulfates in the micelle. We show that there is a strong tendency for the CESTO-Li+ complex to be incorporated into the outer layer of the micelle with a consequence of a drastic reduction of the effective charge of the micelle. Using a two-layer model for the micellar structure factor and a multicomponent ionic solution theory of Khan and Ronis for the intermicellar structure factor, we have satisfactorily fitted all the SANS data at different surfactant concentrations and various molar ratios of CESTO to LDS. The extracted parameters include the micellar aggregation number, the effective micellar charge, and the fraction of CESTO incorporated into the outer layers of the micelle.