Smectic texture

In the case of smectic polymers, observation of specific textures may be difficult. Often textures occur whose characteristics are somewhat obscure and observable only with difficulty even after extended annealing within the smectic phase. However, several variants occur which closely resemble the focal-conic and fan-shaped textures of A and C modifications in LMMLCs.  

Smectic A phases often display textures which are probably based on the focal-conic arrangement but in which the ellipses and hyperbolae cannot always be distinguished in the microscopic image. The chief examples are, firstly, the so-called batonnets. When the 

A homeotropic (also called pseudoisotropic) texture can also form spontaneously at the phase transition, particularly when this takes place on cooling from a homeotropic nematic. The transition is then difficult to observe except by the disappearance of Brownian motion. 

At the transition from a normal isotropic liquid to smectic C, baton-nets may appear first similar to those of smectic A phases. They are, however, divided by inversion walls into domains of different tilt orientation. Accordingly, the smectic C batonnets show regions with different interference colours. 

Smectic C modifications exhibit two microscopic textures the Schlieren texture and the focal-conic fan texture. As previously discussed, the Schlieren texture of the smectic C phase can be distinguished from that of the nematic phase by the fact that it exhibits only singularities with S = 1. Compared to the corresponding texture in smectic A, the broken focal-conic fan texture of a smectic C is less regular and disturbed by additional disclinations. If the C phase is formed on cooling a smectic A phase, then the Schlieren texture will be obtained from a homeotropic A texture and the broken fan texture will be obtained from the simple focal-conic texture of the preceding A phase. 

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The mesophases of LC diols la-lg were also observed directly in polarized optical micrographs taken immediately after melting the sample. Textures were identified only by comparison with published micrographs (2 ), and are therefore tentative. A nematic texture is observed for If (Fig. 2), while more highly ordered smectic textures are observed for Ib-le and Ig (Fig. 3). 

By polarizing light microscopy we saw the typical focal conic smectic texture of the BDVHD hcmopolyester mesophase but observed no distinctive smectic or nematic structure of the BDA/50 EG/50 HD copolyester cooled from the isotropic melt and held in the mesophase many hours. Also on an x-ray diffractometer trace of the copolyester we did not see the characteristic peak due to the spacing between the layers of the smectic mesophase but did see... 

Fig. 13. A Batonet texture of the smectic-A phase of PEI 82i upon cooling from the isotropic melt. B Smectic texture of 83a. C Nematic texture of co PEI 83g...

Chiral compounds on addition to this polyester cause the formation of the typical twisted smectic textures (Figs. 10 and 11) The... 

These are the most striking features of smectic textures [19]. Smectic layers of constant thickness (incompressible, modulus B— oo) form surfaces called Dupin cyclides. We have seen some of them, which have the form of tori including disclinations, see Fig. 4.7b. Such cyclides can fill any volume of a liquid crystal by cones of different size. An example is afocal-conic pair, namely, two cones with a common base. The common base is an ellipse with apices at A and C and foci at O and O , see Fig. 8.30a. The hyperbola B-B passes through focus O. The focus of... 

Figure 3.14 Optical microscopy photograph showing the smectic texture of liquid crystalline epoxy. Reprinted with permission from K. Sadagopan, D. Ratna and A.B. Samui, Journal of Polymer Science Part A Polymer Chemistry Edition, 2003, 41, 3375 2003, John Wiley and Sons Publishers...

SAXS-reflexes gave a peak for the lamellar phase-separation of the blocks. From this the interlayer distance was calculated to be 154 A. The second peak confirms the existence of a smectic texture. The distance of the smectic layers within the LC phase is... 

The experimental data concerning the synthesis and characterization of the copolyethers based on HB, 1,7-dibromoheptane and 1,9-dlbromononane are summarized in Table 5. In contrast to the copolyethers of HMS, which are all amorphous the copolyethers of HB are crystalline and present anisotropic melts exhibiting smectic textures. Examples of heating and cooling DSC scans for the copolymer PHB-7,9-20 are presented in Figure 9. 

A qualitative estimation of the isotropizatlon transition compared to the melting endotherm support smectic type mesophases for all copol3nners. This estimation is enhanced by the typical smectic textures presented by all these copol3nners. Observed smectic textures are Identical to those... 

Figure 1. A smectic A phase extended on the left-hand side, and showing defect lines in the form of conics a smectic rodlet and small germs are floating in the isotropic phase. The mesogenic product, 4-cyano-4 -n-octylbiphenyl (8CB), was added together with a small amount of Canada balsam, and the mixture was observed between crossed polarizers at room temperature. Canada balsam is an isotropic but optically active and fluid resin, extracted from the conifer Abies balsamea, which facilitates the production of regular smectic textures in several thermotropic liquids. Collophony, or rosin, is a stabilized pine tree resin, used to rub violin bows Friedel used this substance not only for his violin, but also to obtain remarkable smectic textures. Scale bar 20 pm.

Very clear evidence for smectic textures in dispersions of the bacterial viruses Pf 1 and fd was obtained by Booy and Fowlei by freeze-fracture electron microscopy. The liquid-crystalline textures revealed by this technique correlate well with polarizing microscopy of magnetically oriented specimens. 

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