A Multinuclear NMR Approach to the Study of the Lyotropic System CTAB-D20

CTAB-D2O liquid crystalline phase (CTAB = cetyltrimethylammonium bromide), type I according to magnetic anisotropy, has been investigated by means of 2H, 14N and 17O NMR at variable temperature. The residual quadrupolar splittings of ali these nuclei evidenced the alignment of the phase in the magnetic field. The interpretation of the data of D2O quadrupolar nuclei, commonly used in the Study of lyotropic liquid crystalline phases, is complicated because 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