Lyotropic external fields

Lyotropic polymeric LC, formed by dissolving two aromatic polyamides in concentrated sulphuric acid, have been studied using variable-director 13C NMR experiments.324 The experimental line shapes at different angles w.r.t the external field were used to extract macromolecular order and dynamic in these ordered fluids. An interesting application of lyotropic LC is for the chiral discrimination of R- and S-enantiomers, and has recently been demonstrated by Courtieu and co-workers.325 The idea was to include a chiral compound 1-deutero-l-phenylethanol in a chiral cage (e.g., /1-cyclodextrin) which was dissolved and oriented by the nematic mean field in a cromolyn-water system. Proton-decoupled 2H NMR spectrum clearly showed the quad-rupolar splittings of the R- and S-enantiomers. The technique is applicable to water-soluble solutes. 

On a side note, Ouskova and co-workers also reported that the composite of magnetic /i-FejOs nanorods in 5CB showed lower threshold voltages than pure 5CB, and that the sensitivity of the nematic liquid crystal to external magnetic fields was increased in the presence of such magnetic nanorods [451]. Finally, several groups interested in the macroscopic organization and orientation of nanorods also reported on the formation of a lyotropic liquid crystal phase induced by the self-assembly of polymer-coated semiconductor nanorods [453—457], which might be used to improve the device performance, for example, of solar cells. 

In addition to the stress-strain measurements already mentioned, the hexagonal lattice constant was measured in a lyotropic LCE as a function of the water concentration [41]. Furthermore it was shown, using X-ray scattering, that a hexagonal phase can be oriented parallel to the preferred direction by applying an external mechanical field. 

In addition to the above lamellar, columnar and optically isotropic phases, there are also lyotropic nematic phases, which usually involve mixtures of a charged amphiphilic, such as simple soap, with an alkanol (a weaker amphiphilic where the head group is an alcohol), together with water and a simple salt. They are termed nematic because, like thermotropic nematics, their optical axes are easily oriented by external magnetic fields. In contrast to thermotropic nematics, the basic units of lyotropic nematics are molecular aggregates with dimensions of about 2-10 nm. In lyotropics, the nematic phase is much less usual than in thermotropic liquid crystals. Lyotropic nematics... 

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