Focal surfaces, textures

While such behavior can be seen in achiral LC phases, driven by surface constraints as illustrated in Figure 8.11, further characterization of the phase responsible for the minority domains in the B2 banana phases shows this to be the first unequivocal example of a bulk fluid conglomerate. It is worth noting here that the EO behavior of the majority domains is achiral Stripes parallel to the layers switch to a SmA-like focal conic texture, which is identical for both signs of the field, as can be seen in Figure 8.22. This EO behavior very clearly appears achiral when observing the switching in motion. 

The Sc phase exhibits four textures including the pseudo-homeotropic texture, the petal texture, the focal-conic texture and the lined texture (Gray and Goodby, 1984). The last occurs when the layer planes are not parallel to the surface. The lined appearance may be similar to what have been discussed for the cholesteric phase, but can also occur as being superimposed on the focal-conics. Examples of such lined and focal-conic... 

S. Shojaei-Zadeh, S.L. Anna, Role of surface anchoring and geometric confinement on focal conic textures in smectic-A liquid crystals. Langmuir 22, 9986-9993 (2006)... 

In the more general case, when the directions of the helical axis in the various parts of the cell are random along the azimuth and are not parallel to the glass surfaces, we have a polycrystalline sample (Fig. 6.1(c, d)), or the so-called focal-conic texture. 

Friedel did however understand the layered nature of smectics, firstly through the stepped edges possessed by smectic droplets with a free surface, and secondly through his detailed studies of the optical microscopic textures of thin films of smectic phases. He understood the optical discontinuities, i.e., the defects, of the smectic focal-conic texture and saw the relationship of the black lines delineating ellipses of different eccentricities and their associated hyperbolae in terms of focal-conic domains which may be divided into a series of parallel, curved surfaces known as Dupin cy-clides. He also understood that the optically extinct homeotropic textures of smectics of the type he studied gave positive uniaxial interference figures consistent with systems of layers lying flat to the surface. His microscopic studies demonstrated the immense value of the optical microscope as a precise scientific instrument in studies of all types of liquid crystal phases. 

In addition to the TN and IPS modes in nematic displays, himdreds of other displays methods were invented and tested over the last 30 years. Out of them the bistable nematic development based on surface flexoelectric interactions, the bistable cholesterics displays based on switching between planar and focal conic textures and the polymer dispersed liquid crystal displays found some applications. None of them, however, offer better than a few milliseconds switching time. 

Texture composed of focal-conic domains of the ellipse-hyperbola type with visible ellipses, or parts of ellipses, located at the boundary surfaces. 

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