Anisotropic dark-field microscopy

In a nematic liquid the director field is not uniform unless an external field of electric, magnetic or mechanical nature is applied. The director may vary in a smooth continuous way around certain points called disclinations, or more abruptly as in domain walls. Characteristic of the nematic structure are the so-called schlieren textures which are readily observed by polarized light microscopy (Fig. 6.23). The dark bands meet at certain points, the disclinations. It should be noted that a dark region indicates that the local molecular director of the optically anisotropic region is parallel to the polarizer or to the analyser, or that the region is optically isotropic. 

Polarizing light microscopy employs crossed polarizers to view the sample. With isotropic specimens, the field of view is dark, while anisotropic, birefringent samples or areas of a sample will appear bright. Polarizing microscopy is employed to view spherulitic structure [66-68] and deformation morphologies (crazes, shear banding) [69] in polymer blends. Samples for... 

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