ANALYSIS OF C-13 NUCLEAR-SPIN RELAXATION PARAMETERS, INCLUDING ROTATING-FRAME RELAXATION-TIMES, IN A SERIES OF MICELLIZED SODIUM ALKANOATES

Sodium octanoate, nonanoate, decanoate, undecanoate, and dodecanoate, dissolved in D2O, have been investigated in monomeric and micellar sta tes by means of C-13 longitudinal relaxation times at the following me asuring frequencies: 22.6, 50, 75, and 100.4 MHz. For the highest surf actant concentrations available, C-13 relaxation times in the rotating frame have also been measured according to an improved methodology. D ata have been analyzed within the framework of the two-step model, tak ing into account the lack of precise knowledge of monomer proportion. Parameters pertaining to the two-step model, namely, correlation times associated with slow and fast motions and order parameters, are discu ssed with regard to the surfactant chain length. It is demonstrated th at C-13 measurements performed at a single frequency are as well able to yield these parameters, provided that they include the longitudinal relaxation time (T1), the nuclear Overhauser effect factor (NOEF), an d the relaxation time in the rotating frame (T1rho).