Molecular models for the smectic A–smectic C phase transition in a system of biaxial molecules
Molecular models for the smectic A–smectic C phase transition in a system of biaxial molecules
复制标题
双轴分子系统中近晶 A-近晶 C 相变的分子模型
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
M. Osipov
中科院分区：
文献类型：
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作者：
M. Gorkunov;M. Osipov
本文在平均场近似下发展了双轴分子系统近晶A-近晶C相变的分子理论。详细考虑了分子双轴性对跃迁的影响，并论证了双轴序参量是如何由倾斜引起的。结果表明，近晶C相低对称性双轴分子的有序性一般可用10个独立的取向序参量来描述，存在3个不同的倾斜角来表征3个有序张量的倾斜。数值计算的顺序参数作为温度的函数的两种模型的双轴分子：分子与两个主轴和分子与一对偏离中心的横向偶极子。发现三个倾斜角之间存在很大差异，这使得不可能严格定义近晶C相中的唯一指向矢。它还表明，双轴相互作用可能导致一个有害的弱层收缩在近晶C相。最后，证明了近晶A-近晶C相变可能直接由双轴分子间相互作用驱动。在这种情况下，分子长轴的倾斜不是一个主要的序参量，它的温度依赖性是非常不同于常规。
A molecular theory of the smectic A–smectic C transition in a system of biaxial molecules is developed in the mean-field approximation. The influence of molecular biaxiality on the transition is considered in detail and it is demonstrated how the biaxial order parameters are induced by the tilt. It is shown that the ordering of biaxial molecules of low symmetry in the smectic C phase is generally described by ten independent orientational order parameters, and there exist three different tilt angles which specify the tilt of three ordering tensors. The order parameters are calculated numerically as functions of temperature for two models of biaxial molecules: molecules with two principal axes and molecules with a pair of off-center transverse dipoles. A substantial difference between the three tilt angles is found, which makes impossible a strict definition of a unique director in the smectic C phase. It is also shown that biaxial interactions may lead to an anomalously weak layer contraction in the smectic C phase. Finally, it is demonstrated that the smectic A–smectic C phase transition may be directly driven by biaxial intermolecular interactions. In this case, the tilt of long molecular axes is not a primary order parameter, and its temperature dependence is very different from convention.
DOI：
10.1103/physreve.75.060701
发表时间：
2007-01
期刊：
Physical review. E, Statistical, nonlinear, and soft matter physics
影响因子：
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作者：
M. Gorkunov;F. Giesselmann;J. Lagerwall;T. Sluckin;M. Osipov
通讯作者：
M. Gorkunov;F. Giesselmann;J. Lagerwall;T. Sluckin;M. Osipov