Pulsed gradient NMR study of anisotropic surfactant diffusion in the caesium perfluoro octanoate/D2O system
- 1 March 1991
- journal article
- research article
- Published by Informa UK Limited in Liquid Crystals
- Vol. 9 (3), 359-367
- https://doi.org/10.1080/02678299108045570
Abstract
We use pulsed field gradient 19F NMR to measure the diffusion coefficients of surfactant molecules in the isotropic and lamellar phases of the caesium perfluoro octanoate (CsPFO)/D2O system. An aligned lamellar sample is created by cooling through the nematic phase in the presence of a 1·4 T magnetic field. The director in the lamellar phase does not respond to ordinary field strengths, thus the aligned sample can be rotated clockwise or counterclockwise to place the director at a magic angle, where measurement of diffusion coefficients becomes possible. From a pair of so-obtained coefficients, we derive the principal values of the diffusion tensor corresponding to the directions parallel and perpendicular to the director (D⊥ and D ⊥). We found D ∥ to be at least 20 times D ∥ a much larger anisotropy than is seen in electrical conductivity and water diffusion in similar systems. These results are compared to electrical conductivity, water and dye diffusion measurements.Keywords
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