Aggregation Behavior of Quaternary Ammonium Dimeric Surfactant C14-s-C14·2Br Micelles

The aggregation behavior of gemini surfactants 14-s-14 micelles in heavy water solutions was studied using 1H NMR relaxation and two-dimensional nuclear Overhauser enhancement spectroscopy (2D NOESY). Spin-lattice and spin-spin relaxation measurements of the protons showed that the motion of the spacer protons and a part of the methylene protons next to the polar head group was seriously restricted. Therefore, these protons should be involved in the formation of the surface layer of the hydrophobic micellar core. The hydrophobic protons that were away from the polar head group were situated internally in the micellar core and moved relatively freely. Relaxation measurements of the 14-s-14 series (s=2, 3, 4) also showed that the molecules were more tightly packed as the length of the spacer decreased. Their motion was relatively more restricted than those of TTAB, the monomeric homologue of 14-4-14. 2D NOESY spectrum of 14-4-14 exhibited the same pattern as that of 16-4-16. This showed that the micelles of 14-4-14 were spherical, and the surface exhibited a saw-toothed form, similar to that of 16-4-16. Consequently, the length of the alkyl chain did not have any effect on the relative arrangement of molecules in the micelles.