New antiferroelectric liquid crystal for use in LCD

In this work, the physical properties of newly synthesized liquid crystalline compound exhibiting two liquid crystalline phases (ferroelectric and antiferroelectric) were studied. Based on the results of differential scanning calorimetry, polarizing microscopy, and photoelastic modulator methods, the temperature dependences of spontaneous polarization, tilt angle, switching time, and birefringence in the ferroelectric, as well as antiferroelectric phases were determined. Furthermore, the influence of the external electric field on the liquid crystalline textures was studied and the phase sequences at heating and cooling were revealed. The temperature dependence of spontaneous polarization was analysed by means of Landau mean-field theory, and the critical parameter β obtained for ferroelectric liquid crystalline and isotropic liquid transition was 0.21 which is close to 0.25, the value characteristic for tri-critical point.     

The properties of ferroelectric compound (S)-(+)-4-(1-methylheptyloxycarbonyl)phenyl 4′-(4-cyanoacetoxybut-1-oxy) biphenyl-4-carboxylate and its ability of an antiferroelectric phase induction in mixtures

Phase transitions and ferroelectric properties of (S)-(+)-4-(1-methylheptyloxycarbonyl)phenyl 4′-(4-cyanoacetoxybut-1-oxy)biphenyl-4-carboxylate will be described in this article. This compound exhibits the synclinic smectic C* phase and it has the ability to induce an antiferroelectric phase in mixtures with the other ferroelectric compounds. New systems with induced antiferroelectric phase and their properties are presented.     

反铁电陶瓷的强电子发射特性研究

采用掺镧锆锡钛酸铅反铁电陶瓷作为阴极材料,研究了脉冲电压激励下陶瓷的电子发射特性.当激励电压为800V、抽取电压为0V时,得到1.27A/cm²的发射电流密度;当抽取电压增加到4kV时,获得1700A/cm²的发射电流密度.分析了发射电流随抽取电压的变化关系,讨论了反铁电陶瓷强电子发射的内在机理.结果表明：掺镧锆锡钛酸铅反铁电陶瓷能够在较低的激励电压(400V)下实现电子发射,发射电流远大于按照Child-Langmuir定律计算出的电流,三接点附近局域反铁电—铁电相变产生初始电子发射,初始电子电离中性粒子形成等离子体,增强了电子发射. 关键词： 铁电阴极 反铁电体 电子发射     

Electro-optical Kerr effect in the isotropic phase of the two antiferroelectric liquid crystal mixtures

We have experimentally studied for the first time the electro-optical Kerr effect and the pre-transitional behavior in the isotropic phase of two antiferroelectric liquid crystal mixtures, W-232 and W-204D, composed of rod-like ester molecules exhibiting the direct smectic-A to isotropic (SmA-I) phase transition. The Kerr law has been confirmed for the two compounds and the variation of inverse Kerr constant with temperature above the smectic–isotropic transition temperatures were determined. Both the mixtures with very broad antiferroelectric phase around room temperature have similar sequence of the phases (i.e., Cr-SmC*A-SmC*-SmA-I). Although, the pre-transitional behavior is usually complex in the isotropic phase of the chiral smectic liquid crystal compounds, the investigated compounds showed a similar behavior compared to that of nematic–isotropic behavior.     

Dielectric measurements of new antiferroelectric liquid crystals

Three new pure antiferroelectric materials, synthesized at the Military University of Technology (MUT), were investigated by dielectric means. Clear relaxation modes were detected, i.e., Soft, Goldstone, low frequency in-phase (P_L) as well high frequency anti-phase (P_H) modes for paraelectric Sm A*phase, ferroelectric Sm C* phase and antiferroelectric Sm C_A* phase, respectively. Additionally, a high relaxation mode in Sm C_A* was found. The relaxation frequencies f_R of the observed modes were calculated from Cole-Cole diagrams.     

Dielectric properties of LC mixture with induced antiferroelectric phase

Mixture of two liquid crystalline components exhibits the antiferroelectric phase in a broad temperature range at room temperatures, though the two components separately do not show an antiferroelectric phase in a temperature range applied. The dielectric spectroscopy technique combined with measurements of the selective light reflection was used for identification and characterization of the phases and subphases existing in the mixture. In the SmC*_A phase, the low frequency mode characteristic of antiferroelectric phase has been detected. In the broad temperature range between SmC*_A and SmA* phases, no relaxation mode has been detected. The soft mode registered near the phase transition to SmA* phase follows the Curie-Weiss law.     

Phase transitions of new antiferroelectric bent-core thiobenzoate

This article reports the results on phase transitions, mesomorphic and electro-optical (EO) properties of new bis [4-(4′-alkylphenylthiocarbonyl)phenyl] isophtalates from a homologous series of banana-shaped thioesters, referred to as IFOSn, when n?=?8, synthesized by us. The IFOS8 compound has two enantiotropic phases: B2 with antiferroelectric order and B6. The mesomorphic properties were investigated by means of three complementary methods: differential scanning calorimetry, polarized light optical microscopy and transmitted light intensity. EO measurements were also carried out.     

Effect of barium titanate nanoparticles of different particle sizes on electro-optic and dielectric properties of ferroelectric liquid crystal

A comparative study of two different particle sizes of ferroelectric barium titanate (BaTiO₃) nanoparticles as a dopant on the molecular structure, spontaneous polarization and dielectric behavior of a pure ferroelectric liquid crystal 6F₆T have been studied. It has been found that there is a remarkable decrease in isotropic temperature of both doped samples as compared to the pure 6F₆T sample. The spontaneous polarization also decreases for both the doped samples and the reduction is more pronounced in case of the dopant with large particle size. The dielectric spectroscopy confirms the presence of soft mode as well as Goldstone mode and also shows the decrease in the value of dielectric permittivity ?' as a function of frequency for both doped samples. The improvised properties of liquid crystal host doped with BaTiO₃ nanoparticles mainly depend upon the synthesis method of nanoparticles and also upon the particle size of dopant.     

Effect of the chiral chain length on structural and phase properties of ferroelectric liquid crystals

Studies of structural and phase properties obtained on several ferroelectric liquid crystalline materials with 2-alkoxypropionate group used as a chiral centre and without any lateral substitution are presented. In dependence on the chiral chain length these compounds exhibit the cholesteric N* phase, the ferroelectric smectic C* and a low-temperature SmX phase. Values of the spontaneous polarization and spontaneous tilt angle have been determined within the whole range of the SmC* phase. A low-temperature SmX phase has been identified as the orthogonal hexatic SmB* phase. The molecular parameters, namely the layer spacing in the SmC* and SmB* phases and the average intermolecular distances (D) between neighbouring parallel molecules in all investigated phases have been determined using the results of the X-ray diffraction obtained on non-oriented samples. The effect of the chiral chain length on mesomorphic, structural and physical properties of the studied ferroelectric liquid crystalline materials is discussed.     

The comparison of the ability for induction of antiferroelectric phase of cyanoterminated compounds by means of miscibility studies

Ability for an induction of the antiferroelectric phase in compounds with a cyano group in a terminal position has been tested by comparison of phase diagrams of their mixtures. Most of the tested compounds do not cause the induction by themselves but they support an antiferroelectric ordering in mixtures. The core comprising biphenylate fragment has a higher tendency to support the antiferroelectric order.     

Planar-homeotropic transition observed for B2 phase of banana-shaped thioester

1,3-Phenylene bis{4-[(4-dodecyloxybenzoyl) sulfanyl] benzoate} (12OSOR) possessing banana-like achiral molecules has been studied by complementary methods to investigate linear dielectric as well as antiferroelectric properties of its B₂ phase. To this end, the following experimental methods were used: differential scanning calorimetry, polarizing microscopy, dielectric spectroscopy and reversal current method. As found, 12OSOR compound with bent-core molecules exhibits only B₂ phase that happens to be antiferroelectric. Dielectric spectra have been measured using the dielectric spectrometer based on Agilent 4294A impedance analyzer. The measurements have been done using HG 5 µm cells (giving homogeneous orientation) with gold electrodes. Thermal, dielectric, and electro-optic properties of 12OSOR are discussed.     

强电场作用下反铁电锆钛酸铅的介电行为研究

采用电滞回线方法和偏置直流电场中叠加小交变电场方法研究了锆钛酸铅反铁电陶瓷材料在强电场作用下的介电行为.测量结果显示，锆钛酸铅反铁电材料的介电常数随外加电场强度呈非线性变化，在反铁电 铁电转变的电场区间形成介电峰.表征极化强度随电场强度变化率的微分介电常数εd峰值出现在反铁电 铁电转换电场强度处，最高达到41000.随着偏置电场增加反铁电向铁电体转变过程中，小信号介电常数εc减小；在电场降低铁电回复成反铁电过程中，小信号介电常数εc增大，小信号介电常数εc峰先于微分介电常数εd峰出现.根据电场作用下反铁电 关键词： 锆钛酸铅反铁电陶瓷 介电行为 强电场条件     

Study and characterization of the smectic X* phase in binary mixtures of thermotropic double hydrogen bonded ferroelectric liquid crystals

Thermotropic double hydrogen bonded ferroelectric liquid crystals (DHBFLCs) composed of N-carbamyl-L-glutamic acid (CGA) and p-n-alkyloxy benzoic acids (BAO) have been investigated. Variation in the molar proportion of X and Y (where X = CGA + 5BAO and Y = CGA + 6BAO, CGA + 7BAO, and CGA + 8BAO) composed of three series yielded 27 binary mixtures. Optical and thermal properties of these mixtures are meticulously studied in the present article. A novel smectic ordering, namely smectic X*, is observed in all the three series. The aim of the investigation is to obtain an abundance occurrence of smectic X* and hence the proportions of the binary mixtures are so chosen that the preamble task is accomplished. Phase diagrams of three series are constructed from the data obtained from polarizing optical microscope (POM) and differential scanning calorimetry (DSC) studies. Odd–even effect, order of the phase transition, thermal stability factor, thermal equilibrium, and optical tilt angle are also premeditated.     

Electrophysical properties of a system with induced antiferroelectric phase comprising cyano compound

The DSC, electrooptic and X-ray results for the system composed of two synclinic compounds CNCH₂COO(CH₂)₆OphPhCOOPhCOOC*H(CH₃)C₆H₁₃ and C₅H₁₁COO(CH₂)₃OPhCOOPhPhCOOC*H(CH₃)C₆H₁₃ are presented. The antiferroelectric SmC*_A phase induces in this system and it was confirmed by physical measurements. It was found out that the mechanism of SmC*_A phase induction is different than in systems comprising compound with perfluoroalkyl chain.     

A diamond anvil cell for the study of fluid mixtures at high temperatures

Abstract

A new diamond anvil cell has been developed to study the phase behavior of fluid mixtures at high temperature. Special care has been taken to achieve good temperature stability and small temperature gradients. Preliminar experiments show that the cell performs well.     

偏振遥感的侦察原理及应用

偏振遥感是一种新的遥感探测方法,它以目标辐射能量的偏振特征作为探测信息,能够很好的分辨目标上低反射区域和目标轮廓,在复杂的背景中提取目标的三维信息。介绍了偏振遥感的基本原理和国内外应用情况,分析了偏振遥感的特点和在识别人工目标方面的优势。     

玻璃-橡胶混合颗粒的力学响应研究

通过直剪实验和离散元模拟, 研究掺杂了橡胶软球的玻璃体系的力学响应. 改变颗粒固体中橡胶颗粒的含量, 研究体系剪切强度以及剪胀变化等特性, 发现随着橡胶颗粒的增加, 会出现剪胀到剪缩的相转变现象, 且混合颗粒固体的弹性有了很大的提高. 实验研究发现, 随着体系中橡胶颗粒含量的增加, 剪切屈服强度值逐渐减小, 体积发生从剪胀到剪缩的相转变现象, 但临界剪切强度在一定橡胶颗粒含量范围内保持一致; 实验所采取的剪切速率下, 应力应变曲线能较好重合, 即实验处于率无关区域; 混合样品的屈服强度值随正压力的增大而增大. 离散元模拟也得到了上述结果, 另外模拟还发现, 随着橡胶颗粒含量的增加, 颗粒的平均配位数增大; 橡胶颗粒含量和正压力对剪胀-剪缩相转变的位置有影响, 橡胶颗粒含量较小时, 在较大的正压力下易发生相转变现象, 且剪胀-剪缩相转变点对应的平均配位数在5.6-5.9之间; 在橡胶颗粒含量小于30%时, 混合颗粒样品的残剪强度与不掺杂的颗粒体系相近; 大于30%时, 残剪强度随橡胶颗粒含量的增加而减小; 残剪强度随正压力加大而增加.     

The influence of the chiral terphenylate on the tilt angle in pyrimidine ferroelectric mixtures

Pyrimidine multicomponent mixture used as a base for the preparation of ferroelectric liquid crystalline mixtures after doping with chiral dopants was tested in the aim of establishing the tilt angle dependence on the concentration of chiral dopant. The compounds being components of this mixture were doped with the same chiral dopant to check the influence of their structure on the tilt angle of ferroelectric mixtures.