Insights into the interactions between dendrimers and multiple surfactants: 5. Formation of miscellaneous mixed micelles revealed by a combination of ¹H NMR, diffusion, and NOE analysis

We studied the formation and growth of miscellaneous mixed micelles in dendrimer and surfactant mixtures. NMR techniques including ¹H NMR titration, diffusion (PGSE and DOSY) measurement, and NOE analysis were used to investigate the shape, size, interaction mode, spatial localization, and molecular orientation of the formed dendrimer/surfactant aggregates at different stages. The results suggest the formation of the following supramolecular aggregates when an equal molar concentration of sodium dodecylsulfate (SDS) and sodium deoxycholate (SDC) were added into a generation 4 (G4) cationic dendrimer: (1) the encapsulation of the two surfactants in the interior pockets of dendrimer at extremely low surfactant concentrations; (2) the binding of SDS on the surface of G4 dendrimer above the saturated encapsulation concentration; (3) the formation of globular SDS micelles and SDC dimer in the aqueous solution above the CMC of each surfactant; (4) the accumulation of SDS molecules on the surface of dendrimer in a bilayer fashion at high surfactant concentrations; (5) the interactions of dendrimer with the globular SDS micelles; and (6) the encapsulation of SDC monomers or dimers in the globular SDS micelles. The competitive binding/encapsulation of the two surfactants at different stages was evaluated. The results provide a new insight into the interactions of dendrimers with mixed surfactant systems.