Cholesteric phase patterns

Fig. 22A-D. Characterization of the liquid crystalline suspensions of A7 phage-ZnS nanocrystals (A7-ZnS) and cast fUm A POM texture of a suspension of A7-ZnS (127 mg/ml) B, C their constructive and destructive interference patterns generated from parallel aligned smectic layers when observed using a differential interference contrast filter D texture of the cholesteric phase of an A7-ZnS suspension (76 mg/ml). (Reprinted with permission from [124], copyright 2000, American Association for the Advancement of Science)...

As with thermotropic nematics, the addition of optically active species to lyotropic nematic phases gives lyotropic cholesteric phases. Whilst details of their structures are not fully established they appear to follow the general pattern outlined above. The cholesteric twist would appear to derive from the packing of optically active mole-... 

Figure 41. Mesogen patterns (bottom to top) cholesteric DNA [63 a, 75] superimposed on early universe computer simulations [12] and Lehmann s paintings of cholesteric phase [14] Taia mesogenic surface human brain [79 a] with continued mesogenic patterns from bottom, reminiscent of mesomorphic relatedness of neuronal-activity patterns [80 a] to mesogenic operation modes and quite recent quests for quantum-computer capacities [80 b].

We have not studied the cholesteric phases found between about 50 % and 80 % of solvent for some copolymers, because X-Ray diffraction patterns of this phase are very poor [one observes only a band at low angles) and do not allow a detailed analysis of the cholesteric structure. 

Like in the nematic phase, the textures of SmC reveal blurred Schlieren patterns with linear singularities of strength s = 1. The singularities of 5 = 1/2 are not observed due to the reduced symmetry (C2h) of the SmC phase. Chiral smectics C are periodic structures and the helical pitch can be measured under a microscope either from the Grandjean lines or as a distance between the lines indicating periodicity, like in Fig. 8.22 for the cholesteric phase. On the other hand, like in... 

Like the APD mode, depending on the materials, the homogeneous texture of the smectic C phase with the stripe-shaped pattern can be formed by direct transition from the cholesteric phase or isotropic liquid phase without an applied electric field. However, most materials having the transition without a smectic A phase, do not exhibit such a homogeneous texture, but forms two kinds of layers at random. 

Figure 10.14. X-ray diffraction of the uniformly aligned TGBct phase of I2F2BTFO1M7 (from [24 and 25]). (a) Difiraction pattern in the plane perpendicular to the pitch axis for a uniformly aligned sample, (b) Angular variation of the intensity along the ring of scattering (/-scan), (c) Diffraction intensity in a plane parallel to the pitch axis ( cu-scan ). Triangles cholesteric phase. Squares TGBc phase.

The blue phase was earlier classified as belonging to the cholesteric phase, but is in fact a separate phase. It is in a sense a crystalline liquid. The molecules are positionally disordered and have no fixed mean positions, but the spatial pattern of molecular orientations can be assigned to a translation group. Usually the blue phase falls between the cholesteric and the isotropic phase, but direct transition to the smectic phase has been observed. Three blue phases have been found, one of them is amorphous. 

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