Fingerprint Texture Transition

Chiral dithienylcyclopentene compounds can also be used to induce the cholesteric-isotropic phase transition [36]. A cholesteric polygonal fingerprint texture was exhibited by 10 wt% of 2 as a mesogenic dopant in a conventional achiral nematic 5CB as shown in Figure 5.6a. The cholesteric phase to isotropic transition temperature for the doped 5CB was 42 C. With UV irradiation at 310 nm (30 mW cm ) for 30 s, the sample went into the isotropic phase (Fig. 5.6b) whereas upon visible fight irradiation at 670 nm a reverse process was reached within 30 min (Fig. 5.6c). 

Figure 7 Liquid-crystal textures observed for PyAG-l 8 under the polarizing microscope as a function of temperature (a) and (b) wormlike textures found in the 60°C to 110°C range (c) the pseudofocal conic texture observed at 110°C (d) the transition phase occurring at 130°C, and (e) the cholesteric fingerprint texture observed at 180°C. (Taken from J. Watanabe and Y. Takashina. Polym. J. 24 709, 1992. With permission.)...

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