CCA-2774 Original Scientific Paper A Multinuclear NMR Approach to the Study of the Lyotropic System CTAB-D2O

CTAB-D2O liquid crystalline phase (CTAB = cetyltrimethylammo-nium bromide), type I according to magnetic anisotropy, has been investigated by means of 2H, 14N and 17O NMR at variable temper-ature. The residual quadrupolar splittings of all these nuclei evi-denced the alignment of the phase in the magnetic field. The inter-pretation of the data of D2O quadrupolar nuclei, commonly used in the study of lyotropic liquid crystalline phases, is complicated be-cause of water reorientation, exchange processes and variations of the hydration degree. The 14N quadrupolar splittings are much more reliable indicators of the orientation of surfactant aggregates since their interpretation in terms of the order parameter is straightforward in this case because the nitrogen nucleus is subject to an electric field gradient of axial symmetry and resides just in the head of the amphiphile. Key words: liquid crystals, NMR spectroscopy, quadrupolar nuclei, surfactants