TITLE

Nuclear spin relaxation in a hexagonal lyotropic liquid crystal

AUTHOR(S)
Quist, Per-Ola; Halle, Bertil; Furó, István
PUB. DATE
November 1991
SOURCE
Journal of Chemical Physics;11/1/1991, Vol. 95 Issue 9, p6945
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
The 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 (NC) phase, we measure the orientation-dependent relaxation rates R1Z and R1Q 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)×10-10 m2 s-1 at 25 °C (activation energy 26±2 kJ mol-1 ) and the counterion surface diffusion coefficient to (4.8±0.9)×10-10 m2 s-1 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 SDC≊0.9.
ACCESSION #
7619455

 

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