Field-induced hexagonal blue phases in positive and negative dielectric anisotropy systems: Phase diagrams and topological properties.
Field-induced hexagonal blue phases in positive and negative dielectric anisotropy systems: Phase diagrams and topological properties.
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正负介电各向异性系统中场诱导的六方蓝相：相图和拓扑性质。
DOI：
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发表时间：
1990
期刊：
影响因子：
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通讯作者：
Shtrikman
中科院分区：
文献类型：
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作者：
Hornreich;Shtrikman
利用朗道理论，考虑了在应用领域中胆甾型液晶中存在六方结构的可能性。研究了正和负介电各向异性系统。研究发现，当各向异性为正时，二维和三维六方相在手性-温度场相图的不同区域是热力学稳定的，而当各向异性为负时，仅出现三维相。这与实验数据一致。此外，理论结果表明，当各向异性为正时，可以存在两种具有相同空间群（P${6}_{2}$22）但不同结构因子的不同三维六方相。考虑通过光学或核磁共振研究验证这一预测的方法。最后，考虑六方相向错的拓扑方面。发现四种稳定六边形结构中的每一种都具有两条单轴正缺陷线和一条单轴负缺陷线。当阶参数被取为单轴指向矢而不是双轴对称张量时，后者是唯一的拓扑向错。
Using Landau theory, the possibility that hexagonal structures can exist in cholesteric liquid crystals in an applied field is considered. Both positive and negative dielectric anisotropy systems are studied. It is found that two- and three-dimensional hexagonal phases are thermodynamically stable in different regions of the chirality-temperature field phase diagram when the anisotropy is positive, while for negative anisotropy only a three-dimensional phase occurs. This is in agreement with experimental data. In addition, the theoretical results indicate that two different three-dimensional hexagonal phases, having the same space group (P${6}_{2}$22) but different structure factors, can exist when the anisotropy is positive. Ways of verifying this prediction by optical or NMR studies are considered. Finally, the topological aspects of disclinations in the hexagonal phases are considered. Each of the four stable hexagonal structures is found to have two uniaxial positive and one uniaxial negative defect line. The latter is the only topological disclination when the order parameter is taken to be a uniaxial director rather than a biaxial symmetric tensor.