1H NMR study on pre-micellization of quaternary ammonium gemini surfactants

Two quaternary ammonium Gemini surfactant series, 12-s-12; ([Cl2H25N+(CH3)(2)](2)(CH2)(2)center dot Br-) and 14-s-14 ([C14H29N+(CH3)(2)](2)(CH2)(5)center dot 2Br(-)) where s = 2,3 and 4, have been studied by the use of H-1 NMR in aqueous solution concentrations below their critical micelle concentrations (CMC) at 25 degrees C. The appearance of a second set of peaks for the 14-s-14 series and the changes in chemical shifts, line widths, and line shapes of the 12-s-12 series with increasing concentration below the CMC are interpreted as evidence for the formation of premicelle aggregates (oligomers) that appear at approximately one-half their CMC values. Self-diffusion coefficients (D) and transverse relaxation times (T-2) have also been detected and support the results obtained by 1H NMR.