Spiral textures

Fig. 11.10 a POM image of the chiral nematic (N -LC) phase of (S)-Poly-4 in 10 wt % lyotropic LC solution in toluene showing a double-spiraled texture. Inset shows a fingerprint texture with a helical half pitch of 1.5 pm. b Schematic representation of the N -LC phase of (5)-PA17. Reprinted with permission from [18]. Copyright 2012, American Chemical Society... 

Figure 11.8. Spiral texture of hexakis-(3,7-dimethyloctyloxy)-phthalocyanine observed between crossed polarizers after quickly cooling from the isotropic phase to room temperature. (Reprinted with permission from Chem. Commun. 1993, 1120 1993, Royal Society of Chemistry [14].)...

McGrath, K. and Kidman, M., Spiral textures in lyotropic liquid crystals First order transition between normal hexagonal and lamellar gel phases, J. Phys. II (France), 3, 903-926 (1993). 

Compound 114d possesses significantly lower transition temperatures (Scheme 60) due to the branched side chains [126]. A columnar phase is present even below room temperature. At 14 °C, anew chiral columnar phase was observed while above 111 °C, an achiral columnar rectangular phase was observed. The spiral-pattern texture of 114d in the chiral Col mesophase is shown in Fig. 17. 

Fig. 17 Spiral-pattern texture of 114d in the Col phase. Reproduced by permission of Taylor Francis (www.informaworld. com) from [127]...

Spiral grain F igure/grain/texture Hardness movement in service ability to stain Newsprint - high speed printing,... 

Textures correspond to various arrangements of defects. When the isotropic liquid is cooled, the nematic phase may appear at the deisotropization point in the form of separate small, round objects called droplets (Fig. 12). These can show extinction crosses, spiral structures, bipolar arrangements, or some other topology depending on boundary conditions. Theoretical studies based on a simple model confirm the stability of radial or bipolar orientation (Fig. 5) [22]. Considerations based on improved theoretical models yield stable twisted... 

The cholesteric texture occurring with perpendicular boundary orientation, on the other hand, is not a uniform texture. Under the microscope the entire field of view is filled with right-and left-handed spirals. This cholesteric texture is known as the scroll texture and appears very much like an end-on view of a bundle of rolled-up scrolls. Capacitance measurements show that the cholesteric helical axis in this texture is still predominantly perpendicular to the plane of the layer. An exact analysis of the structure of this texture, even for the case of equal elastic constants, seems difficult to achieve. Important from the applications point of view is that the scroll texture is adopted without disclinations immediately after a display element is turned off and that this structure is essentially nonscattering. Homeotropic boundary orientation therefore solves the problem of display after-images. 

Convolution kan-v9- lu-shon (1545) . (1) An irregular spiral or twisted condition characteristic of mature cotton fiber. It is visible under a microscopic. The finer fibers are generally more twisted than the coarser fibers. (2) Coil and curl in certain types of textured yarns which provide bulkiness to the yarn. Tortora PG (ed) (1997) Fairchild s dictionary of textiles. Fairchild Books, New York. 

Ratine ra-to- na [F ratine] (ca. 1914) n. (1) A plain-weave, loosely constructed fabric having a rough, spongy texture, which is imparted by the use of nubby phed yarns. It is made from worsted, cotton, or other yarns. (2) A variant of spiral yarns in which the outer yarn is fed more freely to form loops that kink back on themselves and are held in place by a third binder yarn that is added in a second twisting operation. Complete textile glossary. Celanese Corporation, New York. 

Figure 11.3. Chiral microscopic textures between crossed polarizers of the (+) and (—) enantiomers ((a) and (b), respectively) of triphenylenehexayl 3-methylnonanoate (al) and (bl) enantiomorphic opposite points in the high-temperature phase (al,2) and (bl,2) opposite points and spirals at the phase transition (schematic) (a2) and (b2) enantiomorphic spirals in the low-temperature phase. (Reprinted with permission from Nature 298, 46 1982, Macmillan Magazines [4].)...

Apart from the triphenylene mentioned in Section 11.2, one other case has been reported where a chiral columnar phase structure manifests itself in an asymmetric texture 2,3,9,10,16,17,23,24-octakis-(5-3,7-dimethyloctyloxy)-phthalocyanine exhibits two columnar phases above room temperature [8], [14]. The one at the higher temperature has a rectangular column lattice, the other a hexagonal one. When cooled quickly from the isotropic liquid, left-handed spirals appear in the flower-like texture of the highly ordered room temperature phase (Figure 11.8). X-ray and circular dichroism measurements indicate a helical superstructure with a pitch of 55 A (a 16 molecules). It seems very probable that in this case the molecules are weakly tilted and that the tilt direction spirals around the column axis, especially because the phase at higher temperatures is rectangular and therefore most probably tilted as well. 

Two contrasting examples of porous three-dimensional electrodes are shown in Fig, 2.35. The Swiss roJI cell (Fig. 2.35(a)) consists of an electrode-separator or spacer-electrode sandwich spirally wound, usually with axial flow through the mesh electrodes. The mass transport is promoted by textured electrodes and/or plastic mesh turbulence promoters which also serve as membrane-electrode spacers. The interelectrode gap is small (0.2-2 mm), providing a low cell voltage... 

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