Antiferroelectricity and Intermolecular Interactions in Chiral Smectic Liquid Crystals

我们从不同的角度研究了液晶的反铁电性，建立了P_X模型：分子绕长轴的受阻旋转运动在近晶层界附近产生平行于倾斜面的自发极化，并稳定了反铁电SC_A^**>相。本文从P_X模型出发，分析了铁电性与反铁电性之间的挫折，提出了无阈值反铁电性（TLAF）的概念，并解释了在一种新型的反铁电性液晶混合物中观察到的V型开关现象，这种V型开关可用于有源矩阵电极的液晶显示器（LCD）。详细内容是：1）高阶X射线布拉格峰表明稳定的反铁电性与高阶近晶层之间存在相关性。2）光谱学澄清了以下四个事实：（1）偏振拉曼证实了SC^<**>和SC_A^<**>中的分子排列。(2)核磁共振和偏振红外光谱证实了这一结论。 ...更多信息 t结构、旋进运动以及手性烷基链在液晶相中绕平均链轴的双轴性。(3)PIR证明了SC^**>和SC_A^**>分子绕长轴转动受阻，受阻方向不同，三稳态转换的阈值为SC^**>和SC_A^**>受阻方向之间的势垒，提出了P_X模型。(4)PIR证实了手性烷基链的旋进运动，NMR证实了其集体运动的特征。3）在130 fs泵浦脉冲下的光学克尔效应没有出现任何临界慢化，表明激光诱导的分子重取向和极化之间没有耦合<11>。4）在温度梯度下对自支撑膜中亚相的光学显微镜观察支持了Yamashita的ANNNI+J_（？）5）对一种反铁电液晶混合物的电光观察表明，该液晶混合物具有V型反转，从而产生了基于指向矢从层到层倾斜的无规化和Langevin型排列的TLAF。6）PIR和NMR表明，在SI_A^* 中，P_X模型也成立。7）CD光谱证实了SC_螺旋结构的动力学特征<alpha>，支持了SC<alpha>_螺旋结构由热激发C-8）聚亚甲基链上连接的手性单元的二聚体分子表明了偶极-偶极相互作用在SC_A^&lt;**&gt;中的重要性。9）5 T超导磁体简化了液晶盒的制备，进一步研究了取向机制和缺陷结构。少

We have studied antiferroelectricity in liquid crystals from various viewpoints and established the P_X model ; the hindered rotational motion of molecules about their long axs produces spontaneous polarizations parallel to the tilt plane near smectic layr boundaries and stabilizes the antiferroelectric SC_A^<**> phase. Based on the P_X model, we have analyzed the frustration between ferro- and antiferro-electricity, introduced a novel concept, thresholdless antiferroelectricity (TLAF), and explained the V-shaped switching observed in a novel, apparently antiferroelectric liquid crystal mixture and usable in liquid crystal displays (LCDs) with active matrix electrodes. Details are :1) Higher-order X-ray Bragg peaks indicated a correlation between the stable antiferroelectricity and higher smectic-layr order.2) Spectroscopy clarified the following four facts :(1) Polarized Raman confirmed the molecular arrangements in SC^<**> and SC_A^<**>.(2) NMR and polarized IR (PIR) verified the ben … More t structure, the precessional motion and the biaxiality around the average chain axs of chiral alkyl chains in liquid crystal phases.(3) PIR proved the hindrance of molecular rotational motion about their long axs and a difference in the hindered direction between SC^<**> and SC_A^<**>, assigning the threshold of the triastable switching to the barrier between the SC^<**> and SC_A^<**> hindered directions and suggesting the P_X model.(4) PIR verified the chiral alkyl chain precessional motion, and NMR indicted its collective character.3) The optical Kerr effect with 130 fs pump pulses dose not show any critical slowing down, indicating no coupling between the laser-induced molecular reorientation with tau-10^<11>s and the polarization.4) Optical microscope observation of the subphases in free-standing films under temperature gradients supported Yamashita's ANNNI+J_3 model.5) Electro-optical observation of an apparently antiferroelectric liquid crystall mixture showed the V-shaped switching, resulting in the TLAF based on the randomization and Langevin type alignment of director tilting from layr to layr.6) PIR and NMR showed that the P_X model also holds in SI_A^<**>.7) CD spectroscopy proved the dynamical character of the SC_<alpha> helicoidal structure, supporting a speculation of SC_<alpha> characterized by thermally excited C-director disclinations.8) Dimer molecules with chiral units connected with polymethlene chain indicated the importance of dipole-dipole interaction in SC_A^<**>.9) A 5 T superconducting magnet simplified the fabrication of liquid crystal cells, furthering to study the aligning mechanism and the defect structure. Less