The effects of tetraalkylammonium bromides (TAABs) on the micellization of sodium dodecylsulfate (SDS) are studied using pyrene solubilization and several nuclear magnetic resonance (NMR) techniques. Two-dimensional nuclear Overhauser effect spectroscopy (2D NOESY) experiments confirm that tetraalkylammonium (TAA+) ions associate with SDS to form mixed micelles. TAA + ions attach to the surface of the mixed micelles and become inserted into the hydrophobic core of the mixed micelles. Because TAA + ions appear in the hydrophobic interior of the TAA-SDS mixed micelles, the micropolarity inside the mixed micelles sensed by pyrene might not reflect the true hydrophobicity of the micellar core. Using proton chemical shift analysis, the degree of hydration on the surface of the mixed micelles is determined from the chemical shift change of SDS α-CH2 protons. The self-diffusion coefficients of SDS and TAA+ ions in the TAAB/SDS/D2O solutions are measured by using pulse-field gradient NMR, and the fraction of TAA+ ions associated with the SDS to form the mixed micelles is calculated from the self-diffusion data. Moreover, secondary micelle formation for SDS and TAA+ ions is observed on the basis of 1H chemical shift analysis and the self-diffusion data. The 2D NOESY experiments also reveal unusual tumbling behavior of SDS alkyl protons. For Pr4NBr/SDS and Bu4NBr/SDS solutions, positive and negative nuclear Overhauser effects are simultaneously observed among the SDS alkyl protons.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry