| Popis: |
We have produced cylindrically symmetric single crystal textures of the cholesteric and smectic phases of cholesteryl esters by containing them in glass capillaries of smaller than 50 μ radius and inducing shear either by air-pressure changes from one end of the capillary or by volume changes on phase transformations of the sample itself. In the cholesteric phase, when the long axes of the molecules at the capillary interface are aligned parallel to the tube axis, the optic (twist) axes of the weakly negative uniaxial indicatrix are all radially oriented. In the smectic phase, when the molecules are aligned perpendicular to the substrate, the optic axes of the somewhat stronger positive uniaxial indicatrix are again radial. With the molecules aligned parallel to the tube axis, the optic axes of the smectic phase are everywhere parallel to the tube axis. These cylindrically symmetric orientations allow determination of the birefringence of the mesophase. The axial ratios of the refractive index ellipsoids are close to unity, for example, 1.014 and 1.028 respectively for the cholesteric and smectic phases of cholesteryl nonanoate. So far as we know these birefringences have been measured for the first time from cylindrical textures. |
