Proton relaxation study of paraffinic chain motions in a lyotropic liquid crystalThe hexagonal (E) phase in the sodium dodecyl sulphate (SDS)/decanol!water system is investigated by 2H and 23Na nuclear magnetic resonance (NMR) of the selectively deuterated SDS and the sodium counterion. Using macroscopically oriented E phase samples, prepared from the magnetically aligned nematic (N c) phase, we measure the orientation-dependent relaxation rates R lz and RIQ as well as the line shape of both nuclei. The orientation dependence of the lab-frame spectral densities, determined from the relaxation rates, allow us to separate contributions from different types of molecular motion. In particular, we find a dominant contribution from molecular diffusion around the cylindrical aggregate. From this contribution we determine the lateral diffusion coefficient of SDS to (1.4 ± 0.2) X 10 -10 m 2 s -I at 25 ·C (activation energy 26 ± 2 kJ mol -I) and the counterion surface diffusion coefficient to (4.8 ± 0.9) X 10 -10 m 2 s -I at 25 ·C (a factor 2.8 smaller than in an infinitely dilute aqueous electrolyte solution). Furthermore, the flexibility of the cylindrical aggregates in the investigated E phase (aggregate volume fraction 0.27) is quantified in terms of an orientational order parameter ;:::0.9.

Nuclear magnetic resonance (NMR) relaxation of quadrupolar nuclei is introduced as a new method for determining micelle size and nematic order in lyotropic nematic mesophases from the dependence of the spin relaxation rates on molecular diffusion over the curved micelle surface. The approach is illustrated by an experimental study of two uniaxial nematic phases (the calamitic Nc and discotic ND phases of the sodium dodecyl sulphate/decanol/water system) using two nuclei: 2H in the a-deuterated surfactant and 23Na in the counterions. The two nuclei yield similar results: an apparently temperature independent axial ratio of 34 in both phases and a nematic order parameter which decreases from ca. 0.9 (0.75) at the lowest temperature to ca. 0.6 (0.5) at the highest temperature in the Nc (N,) phase. As compared to the predictions of the Maier-Saupe theory, the nematic order parameter in the NC phase is considerably larger and decreases more strongly as the nematic-isotropic transition is approached.

A novel liquid crystalline phase has been identified in the κ-carrageenan/NaI/water system. Solutions of ultrasonically degraded carrageenan were prepared in 0.1 M NaI both by direct mixing and by osmotic compression, and a macroscopic phase separation into one anisotropic bottom phase and one isotropic top phase was found in the concentration range 5−11% (w/w). The properties of the anisotropic phase were investigated by small-angle X-ray scattering (SAXS), 23Na NMR, and polarized light microscopy. The phase could be melted to a completely isotropic solution by heating to 65 °C, and the anisotropic phase slowly re-formed again on standing at room temperature, indicating that the phase is in thermodynamic equilibrium. Intact (nondegraded) κ-carrageenan failed to give macroscopic phase separation but yielded instead birefringent gels for concentrations higher than 2%.

The microemulsion phase of the system AOT-D20-2,2,4-trimethylpentane (TMP) has been studied by water 2H longitudinal and transverse spin relaxation measurements at three frequencies and at temperatures down to -29 "C. Additional information was obtained from n.m.r. signal intensities and quadrupolar line splittings, differential scanning calorimetry and smallangle X-ray scattering. The results establish the existence of reversed micelles with unfrozen aqueous cores containing between 2 and 4 water molecules per AOT. As the temperature is lowered, these micelles grow into very long rods. The rate of water reorientation in the core, obtained directly from the frequency-dependence of the longitudinal relaxation rate, is two orders of magnitude lower than that of bulk water at the same temperature.

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