Self-Diffusion of Water in Polycrystalline Smectic Liquid Crystals

Frank D. Blum, Missouri University of Science and Technology
Alapat S. Padmanabhan
Rana Mohebbi

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The self-diffusion of water in between the bilayers of a smectic liquid crystal has been studied by the NMR pulsed field gradient method. It was found that, for smectic liquid crystals of ca. 75 wt % sodium 4-(1′-heptylnonyl)benzenesulfonate (SHBS)-25 wt % water, a diffusion coefficient of 8 × 10-11 m2/s parallel to the bilayers fit the data. Diffusion perpendicular to the bilayer was found to be much slower. Arrhenius behavior for the diffusion of water was found with an energy of activation of 20.2 ± 1.2 kJ/mol. This is higher than that found in bulk water or salt solutions. It was also determined that crystalline defects or domain boundaries played a negligible role in the NMR behavior. This is in contrast to other systems and probably due to the ability of SHBS-water liquid crystals to form large planar bilayers.