Monomeric And Gemini Surfactants Studied By NMR

In this dissertation, NMR spectroscopy was used to study the aggregation, micelle structure, dynamics and interactaion of a few typical surfactants in aqueous solution. The results include:The variation of ¹H chemical shift of Sodium 4-Decyl Naphthalene Sulfonate (SDNS) solution at 313 K with different concentrations shows that its Critical Micelle Concentration (CMC) of SDNS lies between 0.82 and 0.92 mmol/L, which is in the same range with that at 298 K (reported). Information provided by relaxation and 2D NOESY spectroscopy suggest that the hydrophobic chains in SDNS micelle at 313 K are packed more tightly than that at 298 K. These hydrophobic chains in SDNS micelles are packed densely and theα- andβ- methylene protons next to the naphthalene rings are packed more tightly among the naphthyl rings in the palisade layer to avoid the hydrocarbon-water contact. The T₂ values of protons at different temperatures in the micellar and monomer states show that temperature have a large effect on their motions. The hydration radius of SDNS micelle is approximate 5.3 times of that of monomer by NMR diffusion. The electrostatic repulsion force makes the palisade layer of Sodium Dodecyl Sulfonate (SDSN) micelle packed looser than that of SDNS at 313 K. The characteristics of sodium 4-decyl naphthalene sulfonate (SDNS) / Triton X-100 (TX-100) and sodium dodecyl sulfonate (SDSN) / SDNS mixed micelles of different molar ratios were studied by 1D and 2D ¹H NMR. In the mixed micelle of SDNS / TX-100 the phenoxy rings of the TX-100 are embedded in the near vicinity of the alkyl chains of SDNS and its poly-oxy ethylene segments but the first oxy-ethylene group, to which the phenoxy ring is adjacent, are located near the naphthyl rings. In the mixed micelle of SDNS / SDSN system the sulfonate groups of SDSN are embedded in the naphthyl rings of SDNS, i.e. they are located inner in the mixed hydrophobic micellar core than those of SDNS. Moreover, the naphthyl rings of SDNS separating these sulfonate groups of SDSN may play an active role in weakening the electrostatic repulsion of the negatively charged sulfonate groups, which favors the mixed micelle aggregation.The measurements of self-diffusion coefficient, spin-spin relaxation and inter-proton distance at 318 K suggest that N,N'-bis(cetyldimethyl)-α,ω-alkane propane diammonium dibromide (16-3-16) quasi-global micelles are formed in the dilute solution at a concentration of 0.26 mmol/L and the head groups are in a saw-toothed form staying at the surface of the micelle to overcome the strong electrostatic repulsion force. Relaxation measurements obviously show that the spacer chain is rigid in the surface layer of the hydrophobic micellar core and the side alkyl chains of 16-3-16 are packed more tightly than those of N,N'-bis(cetyldimethyl)-α,ω-alkane butane diammonium dibromide (16-4-16) in the micellar core. The line-shape analysis of the methyl protons at the end of the side alkyl chain of 16-3-16 and 16-4-16 suggests that two possible momentary morphologies of their side alkyl chains situated in the micelle, respectively.