NMR and neutron scattering studies on spherical and rod-like micelles of dodecyltrimethylammonium bromide in aqueous sodium salicylate solutions

✍ Scribed by Noriko Onoda-Yamamuro; Osamu Yamamuro; Nobuki Tanaka; Hiroyasu Nomura

• Publisher: Elsevier Science
• Year: 2005
• Tongue: English
• Weight: 539 KB
• Volume: 117
• Category: Article
• ISSN: 0167-7322
• DOI: 10.1016/j.molliq.2004.08.009

✦ Synopsis

The effect of sodium salicylate (NaSal) additives on micellar structure and dynamics in aqueous solution of dodecyltrimethylammonium bromide (DTAB) has been studied by means of 1 H-NMR and quasielastic neutron scattering (QENS) measurements. The molar ratio R (=C NaSal /C DTAB ) dependence on the peak shape of the NMR spectra revealed that a sphere-to-rod-like micellar transition took place around R=0.5. The chemical shift for the 1 H atoms of the alkyl group of DTA + ion gave the information for the binding site of Sal À ion in micelles. The R dependence on the chemical shift for the aromatic group of Sal À ion clarified the selective binding feature of Sal À ion in micelles. The dynamic structure factor, S( Q,E), of the micellar molecules exhibited apparent broadening of the elastic scattering peak which was fitted well to a single Lorentzian function. The self-diffusion coefficient D was obtained from the Q-dependence of the HWHM of the Lorentzian function. The slope of D vs. R curve changed around the transition ratio (R=0.5), reflecting the dynamic slowing down of the local relaxational motion of the micellar molecules in rod-like micelles.