Abstract: The self-aggregation of sodium tetradecyl sulfate[n-CH₃(CH₂)₁₃OSO₃Na(STS)] and tetradecyl triethoxylated ether[n-CH₃(CH₂)₁₃O(C₂H₄O)₃H(C₁₄E₃)] in aqueous solution and the interaction between them were studied by 1H self-diffusion coefficient, relaxation measurements and two-dimensional nuclear overhauser enhancement spectroscopy(2D NOESY). When pure anionic surfactant(STS) formed micelles, the α-CH₂ groups were located on the surface layer of the hydrophobic micellar cores. The hydrophobic chains of STS are packed in the interior of the micellar cores. Pure nonionic surfactant(C₁₄E₃) formed large micelles in aqueous solution which is evidenced by the appearance of the small broad peaks of the protons on the hydrophobic chain of C 14E 3. 2D NOESY experiments give the evidence that mixed micelles are formed when STS and C₁₄E₃were mixed in aqueous solution. The relaxation measurement shows that α-CH₂ and β-CH₂ of STS and the α-CH₂ and β-CH₂ of C₁₄E₃locate on the surface layers of the mixed micellar cores. The hydrophilic moieties(CH₂CH₂0)₃ of the nonionic surfactant crimpe around the hydrophobic micellar cores. The self-diffusion coefficient measurement shows that the mixed micelles are larger than the pure micelles of STS. Softer and more incompact shells surrounding the micellar cores are created by the hydrophilic chains in C₁₄E₃micelles and STS/C₁₄E₃mixed micelles. The motion of the C₁₄E₃protons are more free in chloroform medium, but the appearance of weak cross peaks shown in the 2D NOESY map of this solution suggests that small self-aggregates may be formed.

Key words: Self-diffusion coefficient, NMR relaxation, 2D NOESY, Mixed micelles