Interaction between sodium tetradecyl sulfate-tetradecyl triethoxylated ether surfactants in aqueous solution by 1H NMR

The self-aggregation of sodium tetradecyl sulfate[n-CH3(CH2)(13)OSO3Na (STS)] and tetradecyl triethoxylated ether [n-CH3(CHZ)(13)O(C2H4O)(3)H(C14E3)] in aqueous solution and the interaction between them were studied by H-1 self-diffusion coefficient, relaxation measurements and two-dimensional nuclear overhauser enhancement spectroscopy(2D NOESY). When pure anionic surfactant(STS) formed micelles, the alpha-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 C14E3. 2D NOESY experiments give the evidence that mixed micelles are formed when STS and C14E3 were mixed in aqueous solution. The relaxation measurement shows that a-CH2 and beta-CH2 of STS and the alpha-CH2 and beta-CH2 of C14E3 locate on the surface layers of the mixed micellar cores. The hydrophilic moieties (CH2CH2O)(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 C14E3 micelles and STS/C14E3 mixed micelles. The motion of the C14E3 protons 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.