Smectic polygonal textures, 9, 331 focal conic

Fig. 25. Arrangement of a smectic A polygonal texture (a) general view of the focal-conic domains filling space efficiently (b) cross-section of the domains showing arrangement of...

Fig. 1.1.7. Focal conic textures in smectic A. (a) The polygonal texture. Crossed polarizers. (Friedel. ) (6) Simple fan-shaped texture. Crossed polarizers. (Sack-...

Figure . Stereoviews of smectic A textures of 8CB (see Fig. 1). (a, b) A stereo-pair in natural light, showing focal conics, each ellipse being penetrated by a branch of a hyperbola passing through one of the two foci of the corresponding ellipse, (c, d) A stereopair of a polygonal texture, with ellipses in the two separated planes of the slide and the cover-slip. Scale bar 100 im.

We have already considered the polygonal networks of cholesteric liquids, which assemble saddle-shaped layers close to Dupin s cyclides, and the focal segments of which differ from those of focal conics (see Sec. 7.4.3). Friedel and Grandjean [21] described in smectic A phases a texture much closer to Dupin s cyclides, with genuine focal conics. As for cholesterics, this texture is obtained when a thin film of the isotropic phase of the mesogenic compound separates the mesophase from the two glasses. 

More recently it has been proved that it is possible to prepare cholesteric homopolymers.Krigbaum et al. observed fan-like texture for polyester synthesized from 4,4 -dihydroxy-a-methylstilbene and (+)-3-methyladipic acid. These authors suggested the formation of a strongly twisted cholesteric. Indeed, in low molecular weight cholesterics with high twist, the defects and textures resemble those of smectics, especially smectic A. Such cholesteric substances may yield non-planar textures. They may appear in fan-shaped, focal conic or polygonal textures. In the case of... 

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