Fan-shaped texture

Fig. 9. Smectic fan-shaped texture observed between crossed polarizers. Courtesy of G. H. Brown, Liquid Crystal Institute, Kent State University.

Hexagonal mesophases can be recognized by their typical fan-shape texture (Fig. 7a). Lamellar mesophases typically show oily streaks with inserted maltese crosses (Fig. 7b). The latter are due to defects, called confocal domains, that arise from a concentric rearrangement of plane layers. In some lamellar mesophases these defects prevail. Hence no oily streaks occur but maltese crosses are the dominant texture (Fig. 7c). 

The smectic mesophases of the thermotropic liquid crystals show a variety of textures but resemble mainly the fan-shape texture of the lyotropic hexagonal meso-phase. For further reading more comprehensive literature is recommended [11]. 

Kricheldorf also reported the synthesis of a thermotropic polyetherimide based on biphenyl-3,3, 4,4 - tetracarboxylic anhydride, and a, -bis(4-ami-nophenoxy) alkane. He similarly observed the need for aromatic rings additional to the two in the anhydride. Batonet and fan-shaped textures indicative of smectic A phases were observed [44] (20). 

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-...

POM characterization revealed that Poly-2 has a batonnet-like texture from 125 to 94 °C and a fan-shaped texture from 94 to 80 °C during the cooling process. On the other hand, Poly-3 has a sandy texture from 142 to 112 °C and a batonnet-like texture from 112 to 93 °C during the cooling process. XRD measurements revealed that Poly-2 has a discotic nematic (No) phase at higher LC temperatures and a discotic lamellar (Dl) phase at lower LC temperatures. Poly-3 showed a Nq phase and a hexagonal columnar (CoL) phase at higher and lower LC temperatures, respectively. The phase transition temperatures of Poly-2 and Poly-3 are summarized in Table 11.2. 

Fig. 11.18 Polarizing optical micrographs under crossed polarizers of Poly-8 at 140 °C in cooling a before applying an electric field (SmC ), b with an applied field of -1-10 V (SmC) and c with an applied field of — 10 V (SmC). The stripes of the fan-shape texture in SmC phase disappeared by applying an electric field to give an ordinary fan-shape texture of SmC phase. The direction of the polarization in the fan-shape texture became inverse when opposite electric current was applied. Reprinted with permission from [14]. Copyright 2008, Wiley...

Fig, h. Transient fan-shaped texture observed upon cooling from the smectic A state for polyester prepared from di-n-propyl p terphenyl carboxylate and H0-CH(CH2)-CH(CH2)-0H.Crossed polarizers. 

It is very simple and vivid method [1]. One can observe characteristic streaks (Schlieren-textures) showing particular macroscopic defects, e.g., disclinatimis and establish the phase symmetry. In Fig. 4.1a the characteristic defects of the nematic phase (disclinations), are well seen. Fan-shape texture of the smectic C phase is shown in Fig. 4.1b. One can also distinguish between different types of uniform molecular orientation in different liquid crystal preparations using a cono-scopy technique (microscopic observations in the convergent light beam) in this case symmetry of the pattern corresponds to the texture symmetry. 

Fig. 4.7 Smectic A fan-shape texture (a) and the structure of typical defects (b)...

SmA phase, the stepped drops as well as polygonal and fan-shape textures are also observed. 

THF and chloroform. It was found from measurements using a polarizing optical microscope that PCBT and PPCHT exhibit fan-shaped and polygonal textures, respectively, in the cooling process, indicating monotropic mesophases. The typical fan-shaped texture of PCBT is shown in Figure 12.1. Furthermore, analysis of the X-ray diffraction patterns and molecular mechanics calculations demonstrated that the LC phase observed in the polymers is assignable to a smectic A2 phase. 

The precursor 6 exhibits the enantiotropic nature of chiral nematic (N ), chiral smectic C (SmC ) and chiral smectic I (SmI ) phases. The shell-printed texture of the SmC phase and the rose-like texture of the SmI phase can be clearly seen in Figure 12.6. The thiophene monomers, M2 and M3, show enantiotropic N, SmA and SmC phases. The SmC phase is characteristic of ferroelectricity. The polymers show various mesophases. The phase transition temperatures are summarized in Table 12.4. PI shows an enantiotropic SmA phase. P2 shows enantiotropic SmA, SmC and SmB phases. The fan-shaped texture of the SmA phase and the striated fan-shaped texture of the SmC phase are shown in Figure 12.7. P3 shows an SmA phase in the heating process and SmA and SmX phases in the cooling process. XRD analysis suggests that the SmX phase of P3 might be a higher order smectic phase. 

Figure 12.7 Polarizing optical micrographs of P2. (a) Fan-shaped texture of smectic A (SmA) phase at 194°C fbj striated fan-shaped texture of chiral smectic C (SmC ) phase at I44°C. From H. Narihiro, X.-M. Dai, H. Goto, K. Akagi, Synthesis and properties of polythienylene derivatives with fluorine-containing chiral liquid crystalline substituents (I), Mol. Cryst. Liq. Cryst, 365, 363 -371 (2001), reprinted by permission of the publisher (Taylor Francis Ltd, http //www.tandf.co.uk/journals)...

Between crossed polarizers, the phase transition into a columnar phase is often accompanied by a dendritic growth of the texture. If the director is oriented perpendicular to the viewing direction, pseudo-focal conic fan-shaped textures can be observed. If the viewing direction is parallel to the director, a platelet texture is formed. 

The SmC analog nature of the lyotropic phase was demonstrated by the observation of characteristic textures associated with the thermotropic SmC phase, such as broken fan-shaped texture, schlieren texture, zigzag defects, spontaneous tilt domains in the surface-stabilized state and pitch lines. Further evidence was provided by X-ray experiments. The two-dimensional dififaction pattern of an aligned sample confirms that the phase is lamellar, tilted and fluid. 

FIGURE 19 Polarizing micrographs of Fe-based PPCH803A polymer (a) fan-shaped texture with no external force (b) aligned with magnetic force held of 0.7 Tesla where magnetic held is parallel to the horizontal direction. 

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