Induced smectic ordering and blue phase formation in mixtures of cyanobiphenyls and cholesterol esters

Natalia A. Kasian, Longin N. Lisetski, Serhii E. Ivanchenko, Vitalii O. Chornous, Halyna V. Bogatyryova, Igor A. Gvozdovskyy
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Abstract

It has been found that in mixtures of nematic E7 and smectogenic cholesteryl oleyl carbonate (COC) the S$_A$-N* transition temperature is substantially (by ~20 K) increased, as compared with pure COC, at E7 concentrations around ~40%. Within the same concentration range, the isotropic transition is preceded by formation of blue phase, with its maximum width of ~3.5 K clearly correlated to the increased thermal stability of the S$_A$ phase. With other cholesterol esters or cyanobiphenyls (cholesteryl nonanoate, 5CB), this effect was either much weaker or not observed. No enhancement of smectic phase was noted when E7 was replaced by N$_{tb}$-forming nematic mixture based on CB7CB with two cyanobiphenyl moieties. Selective Bragg reflection of light (BRL) spectra were measured in all three temperature regions, including the unwinding of the cholesteric helix on cooling towards S$_A$ phase and characteristic selective BRL changes in the blue phase. In the latter case, the measured {\lambda}$_{max}$ values were dependent both on the helical twisting power in the cholesteric phase and on the lattice size and orientation in the blue phase. Also considered were the effects of ferroelectric BaTiO$_3$ nanoparticles accumulated at disclination lines upon the blue phase thermal stability.
氰联苯和胆固醇酯混合物中的诱导胶凝有序和蓝相形成
研究发现,与纯 COC 相比,当 E7 浓度约为 40% 时,在向列 E7 和致密胆绿碳酸酯 (COC) 的混合物中,S$_A$-N* 转变温度会大幅提高(约 20 K)。在相同浓度范围内,各向同性转变之前会形成蓝相,其最大宽度约为 3.5 K,这与 S$_A$ 相热稳定性的提高明显相关。对于其他胆固醇酯或氰基联苯(壬酸胆固醇酯,5CB),这种效应要么弱得多,要么没有观察到。当 E7 被 N$_{tb}$ 取代,形成基于 CB7CB 的向列混合物(具有两个氰基联苯基团)时,没有观察到漆膜相的增强。在所有三个温度区域都测量到了选择性布拉格光反射(BRL)光谱,包括冷却至 S$_A$ 相时胆甾烷螺旋的解旋以及蓝相中特有的选择性布拉格光反射变化。在后一种情况下,测得的{λ}$_{max}$值既取决于胆甾相中的螺旋扭转力,也取决于蓝相中的晶格尺寸和取向。此外,还考虑了铁电体 BaTiO$_3$ 纳米粒子在分离线处的积累对蓝相热稳定性的影响。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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