Two-state model for theSmAPRphase with randomized layer polarization exhibited by some compounds with bent-core molecules,Physical Review E

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Two-state model for theSmAPRphase with randomized layer polarization exhibited by some compounds with bent-core molecules
Physical Review E ( IF 2.2 ) Pub Date : 2022-09-12 , DOI: 10.1103/physreve.106.034702
N V Madhusudana ₁

Affiliation

One of the unusual liquid crystalline phases exhibited by some compounds with bent-core (BC) molecules is designated as

Sm A P_{R}

, in which transverse polarization (P) of smectic layers with upright molecules has a random orientational distribution. Most of such compounds undergo a transition to the

Sm A P_{A}

phase with antiferroelectric order of adjacent layers as the temperature is lowered. Second harmonic studies have shown that the medium consists of polarized domains with only a few hundred molecules, the number increasing at lower temperatures. This is in contrast to the random orientations of entire layers predicted by a few phenomenological models which have been proposed for the

Sm A P_{R}

phase. In this paper we show that the two-state model, developed earlier by us to describe modulated phases found in compounds with BC molecules, can successfully account for all the experimental results on the

Sm A P_{R}

phase. It is proposed that polarized domains which are made of ground state conformers, with a large bend of the aromatic cores, nucleate as circular disks in a first order transition from the isotropic phase. Excited state conformers (with a smaller bend) freely rotate about their long axes and surround the disks. The polarization in the disk has a spontaneous splay distortion which generates a texture with an expelled center of a partial disclination. The interdisk electrostatic energy is lower than the thermal energy and the disks are subject to significant rotational fluctuations, resulting in the uniaxial symmetry of the medium. Calculated equilibrium properties of the medium as functions of temperature and electric field reflect the trends seen in experiments. The model overestimates properties such as the radius of the disks as the transition to a lower temperature uniform phase is approached, and physical arguments are given to show that interlayer interactions ignored in the model become important in that regime, and should be included for an improved description of the medium.

中文翻译：

一些具有弯曲核心分子的化合物表现出具有随机层极化的SmAPR相的两态模型

一些具有弯曲核心 (BC) 分子的化合物表现出的一种不寻常的液晶相被指定为

钐 一个 磷_{R}

，其中具有直立分子的近晶层的横向极化（P）具有随机取向分布。大多数这样的化合物经历转变为

钐 一个 磷_{一个}

随着温度的降低，相邻层的反铁电序相。二次谐波研究表明，介质由只有几百个分子的极化域组成，在较低温度下数量增加。这与一些已经提出的现象学模型预测的整个层的随机方向形成对比。

钐 一个 磷_{R}

阶段。在本文中，我们展示了我们之前开发的用于描述在含有 BC 分子的化合物中发现的调制相的两态模型，可以成功地解释所有实验结果。

钐 一个 磷_{R}

阶段。有人提出，由基态构象异构体构成的极化畴，具有较大的芳香核弯曲，在各向同性相的一级跃迁中以圆盘的形式成核。激发态构象体（具有较小的弯曲）围绕它们的长轴自由旋转并围绕磁盘。圆盘中的极化具有自发的张开畸变，其产生具有部分向错的排出中心的纹理。盘间静电能低于热能，并且盘受到显着的旋转波动，导致介质的单轴对称。作为温度和电场函数的介质的计算平衡特性反映了实验中看到的趋势。

更新日期：2022-09-13

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