ZhETF 87, 450 (1984)[Sov. Physстатья

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[1] Kizel V. A., Prokhorov V. V. Zhetf 87, 450 (1984)[sov. phys // Journal of Experimental and Theoretical Physics. — 1984. — Vol. 60. — P. 257. The existence of two thermodynamically stable blue phases (BP) in chiral liquid crystals has now been established.(l,2) In this work, we measured the circular dichroism (CD) of a mixture of cholesterol nonanoate and cholesterol chloride in a ratio of 73 : 27 molar percent. Chromatographically pure substances were used. Qualitatively similar results were obtained for two other mixtures. The measurements were performed on a Mark-III Jobin Yvon dichrograph. Quartz cells, polished to l/2 of a strip with a thickness of 6 um, were used. The orientation of the structures was fixed by the boundary surface, for which the walls of the cell were coated with a thin layer of polyvinyl alcohol and rubbed in a particular direction. The uniformity of the structure within the boundaries of the entire specimen was monitored by observation under a polarizing microscope. The temperature of the specimen was held constant to within 0.005'C. The angle of incidence (theta) and the azimuth of the direction of rubbing (fi) relative to the incidence plane could be varied over the ranges O-25' and 0-360', respectively, by rotating the thermostat as a whole. All phases give several chiral reflections and, correspondingly,peaks in the CD (Figs. l-3). The CD spectra of the low-temperature phase BP-I depend on the thermal history. Figure I shows curves of CD for BP-I, obtained by cooling from the high-temperature phase BP-II. Figure 2 shows the curves with heating from the usual cholesteric phase(ChP). The position of the reflections of CD in BP-II did not depend on the thermal history. Figure 3 shows data for BP-II, obtained by heating from BP-I.

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