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

Two quaternary ammonium Gemini surfactant series, 12-s-12, (C(12)H(25)N+ (CH(3))(2)(CH(2))(s).(2)Br(-)) and 14-s-14 (C(14)H(29)N(+)(CH(3))(2)(CH(2))(s).(2)Br(-)), where s = 2, 3, and 4, have been studied by the use of (1)H NMR in aqueous solution at 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 (1)H NMR.