Birefringent textures

A preliminary X-ray diffraction study of polymer 11A showed absolutely no crystallinity. A 70 weight % solution of this polymer in NMP showed an almost identical X-ray diffraction pattern with a slightly broader peak width, implying that the birefringence texture has more resemblance to that of the neumatic phase. 

Fig. 5 (a) Molecular structure of dendron-helical polypeptide (DHP) copolymers, (b) Optical birefringent texture of THF solution of DHP (40 wt%) and proposed layered structures of LC state (inset), (c) SAXS profile of dried solid of THF solution. Reproduced from [48] with permission of The Royal Society of Chemistry... 

Between crossed polarizers, a random multidomain birefringent texture is seen. The effect can be reversed by a heat pulse, causing the film to be heated to the N phase, which becomes realigned homeotropically. Typical materials that show this effect are (6) and (7). 

FIGURE 2.2 Examples of liquid crystal birefringence textures imaged at lOOX magnification (a) a homeotropic texture of a columnar phase and (b) "fingerprint" texture of the cholesteric phase growing in from the isotropic liquid phase (black regions). 

For phase identification, therefore, it is essential to be familiar with the different birefringence textures each phase can exhibit. These textures depend on molecular alignment with respect to the optical axis and the polarizers. To illustrate this, we can consider the Schlieren texture of the nematic phase shown in Figure 2.22. 

Schlieren texture A planar liquid crystal birefringence texture characterized by dark brushes. ... 

Fig. 8 a An optical micrograph between cross-polarizers shows the scaffolded solid polystyrene has a birefringent texture (Iwt. % of 11) at 100 °C. b TEM image of a thin film (75 nm thick) ultramicrotomed from the scaffolded material (containing 1 wt. % 11) and stained with osmium tetroxide. Reprinted with permission from [51]. (2002) Wiley... 

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