A de Vries (SmC*) Phase in a Novel Series of Chiral Fluorinated Organosiloxane Liquid Crystals

The synthesis and characterization of a series of five chiral fluorinated low molar mass (bifurcated tail) organosiloxane materials is presented. The mesogenic moiety is similar to that in the TSiKN65F mesogen reported by Naciri et al., which displays a de Vries-type SmA* phase. The one parameter varied across the series reported herein is the length of the alkyl chain linking the mesogen's core to the bifurcated siloxane tail. One of the five materials displays a de Vries SmC* phase upon cooling from SmA*.     

Dynamics of the Reorientation of a Ferroelectric Liquid Crystal Under an Electric Field Studied by Time-Resolved Optical Waveguide Spectroscopy

Abstract

The dynamic structure and molecular reorientation of a ferroelectric liquid crystal induced by an alternating electric field have been investigated by time-resolved optical waveguide spectroscopy (TROWS) in which the transient waveguide mode patterns were recorded as a function of both time and angle of incidence of a probe beam. A ferroelectric liquid crystal, 4-(2S, 3S)-[2-chloro-3-methylpentanoyloxy]-4′-octyloxybiphenyl (3M2CPOOB) was utilized, which showed a fast response to an external electric field in the order of a microsecond. Under a high electric field, it forms the so-called bookshelf structure in which the director of 3M2CPOOB is tilted by 22.5° away from the smectic layer normal in the SmC* phase. Time-resolved waveguide mode patterns were successfully obtained with a time-resolution of 1.0 μs which enabled us to determine the transient features of dielectric tensor of 3M2CPOOB molecules in three dimensional coordinate system. A model that the molecular reorientation coupled with the layer buckling and the rotation around the cone was proposed from the quantitative analysis of the TROWS data.     

Fredericks Transition in Pure and Nanodoped Surface Stabilized Ferroelectric Liquid Crystals

Recently, ferroelectric liquid crystals (FLCs) doped with nanoparticles have attracted a wide interest not only from a scientific but also from a practical point of view and there is continuously growing interest in the effects caused by doping the ferroelectric nanoparticles. Furthermore, the presence of external fields exhibits a very interesting transition, reported by recent experiments. In this work, we investigate the response of a surface stabilized ferroelectric liquid crystal (SSFLC) doped with ferroelectric nanoparticles to an applied electric field. We assume that the smectic layers consist of uniform planes with a fixed orientation and the system is free from dislocation of constant layer thickness due to nanoparticles. We obtain the threshold field of orientational transition and the maximum deviation of the polarization vectors for a pure and a doped SSFLC medium. Then, we discuss the Fredericks transtion of the system and formation of inhomogeneous texture. It is found that the ferroelectric nanoparticles have significant influences in ordering behavior of a SSFLC medium and the threshold fields are critically changed by doping nanoparticles in the SSFLC, which is fundamental to operation of many liquid crystal devices.     

Blue Phase in Liquid Crystal Polymer Mixtures

Blue phases are observed in mixtures of a low molecular weight cholesteric and a nematic polymer. Phase diagrams, optical properties and textures of these mixtures are reported and compared to the case of low molecular weight cholesteric-low molecular weight nematic mixtures.     

Electrical Conductivity of Liquid Crystal Mixtures with Induced Smectic Phases

The electrical conductivity of the two liquid crystal mixtures N-(4-ethoxybenzylidene)-4′-amino benzonitrile (PEBAB)/4,4′-di-n-hexyloxy-azoxybenze (HEXOAB) and 4-n-heptyloxy-4′-cyanobiphenyl (7 CBP)/HEXOAB, which exhibit induced smectic A phases is investigated. In the smectic phases, the conductivity anisotropy of the PEBAB/HEXOAB mixtures is negative at the lowest PEBAB concentrations; this behaviour is usually expected for a smectic layer structure. With increasing PEBAB concentration the anisotropy increases and becomes positive. Possibly, this is an indication for a growing double layer structure, which was observed in polar smectic phases. In the nematic phases the conductivity anisotropy of the pure HEXOAB is considerably reduced by adding a relatively small amount of the polar component. An addition of 10 mole% 7 CBP reduces the anisotropy ratio of the electrical conductivity to V = K_∥/K ₁ ≈ 0.2, which probably is the lowest value observed in a nematic phase so far. Besides the negative conductivity anisotropy, these mixtures also exhibit a positive anisotropy of the dielectric constant. They thus fulfil the conditions for inverse dynamic scattering.     

高居里温度铁电单晶PIN-PT的机电性能

弛豫铁电单晶Pb(In_1/2Nb_1/2)O₃-PbTiO₃(PIN-PT)相较于常用的Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃(PMN-PT)具有更高的居里温度,在高稳定性、高性能的传感器、换能器方面具有应用前景。本工作采用谐振法研究了[001]方向极化的0.66PIN-0.34PT铁电单晶的全矩阵机电性能参数。0.66PIN-0.34PT 单晶的三方-四方相变温度(T_RT)约为160 ℃,居里温度(T_C)约为260 ℃,室温压电系数d₃₃、d₃₁、d₁₅分别为1 340 pC/N、-780 pC/N、321 pC/N,介电常数ε^T₃₃、ε^S₃₃、ε^T₁₁、ε^S₁₁分别为2 700、905、2 210、1 927,机电耦合系数 k₃₃、k₃₁、k₁₅、k_t分别为 87%、58%、38%、61%。其纵向压电常数(d₃₃)和纵向机电耦合系数(k₃₃)小于 PMN-PT 单晶,但是横向压电性能(d₃₁)和剪切压电性能(d₁₅)都略高于PMN-PT单晶。另外,研究了机电耦合性能随温度的变化趋势,发现0.66PIN-0.34PT单晶在150 ℃以下有较好的温度稳定性。     

A Study of a Ferroelectric Liquid Crystal Using Second Optical Harmonic Generation

The phase-matched generation of the optical second harmonic was investigated in the chiral smectic C* phase of a classical ferroelectric liquid crystal (DOBAMBC). The phase-matching was achieved either by incidence angle or by temperature tuning. The temperature behaviour of the second order nonlinear susceptibility was studied.     

高相变温度弛豫铁电单晶PMN-PT-PZ的生长与性能表征

按照0.624Pb(Mg1/3Nb2/3)O3-0.336PbTiO3-0.04PbZrO3化学式所示组分比例,采用分步高温固相反应合成出PMN-PT-PZ多晶,通过熔体坩埚下降法生长出尺寸φ25 mm×90 mm的PMN-PT-PZ单晶.应用X射线衍射对所获多晶和单晶试样进行了物相分析,测试了PMN-PT-PZ晶片的介电温谱、电滞回线和压电常数.结果表明,所得三元固溶体单晶PMN-PT-PZ为不含焦绿石相的纯钙钛矿相结构,其三方-四方相变温度Trt达130℃,居里温度Tc为165～ 170℃,取自单晶原坯三方相区段的(001)取向晶片的压电常数d33在1300～ 1800 pC/N之间;其矫顽电场Ec为4～ 4.5 kV/cm,剩余极化强度Pr为20 ～ 31.5μC/cm2.跟PMN-PT单晶比较,PMN-PT-PZ单晶仍具有较大压电常数d33,而三方-四方相变温度明显提高,其矫顽电场有所增大.     

Electro-Optical Properties in Polymer-Stabilized Blue Phase of n-OCB Homologue Chiral Nematic Liquid Crystal Mixtures

In this study, the chemical structures and physical property dependencies of the electro-optical properties were investigated in polymer-stabilized blue phase (BP) using the four kinds of 4-n-alkyloxy-4′-cyanobiphenyl (n-OCB) homologue chiral nematic LCs. It was confirmed that the optical response time and Kerr coefficient in polymer-stabilized BP was varied with the molecular parity as determined by the alkyl chain length of the n-OCB homologue chiral nematic LC mixtures.     

Synthesis and Liquid Crystal Behavior of a Novel Ester Homologous Series

A novel ester homologous series of 4-[4’-n-alkoxy cinnamoyloxy] benzyl benzoates has been synthesized. The series consists of 12 homologues. Liquid crystal properties commence from the sixth member to the last member of the series with the exhibition of an enantiotropic nematic phase without the exhibition of any smectogenic mesophase. The remaining homologues do not exhibit liquid crystal behavior. The texture of the nematic phase is of the threaded or Schlieren type. The solid-nematic or isotropic transition curve adopts a zigzag path and the nematic-isotropic transition curve steeply rises and then falls in the phase diagram and behaves in normal manner. An odd–even effect is absent in the nematic-isotropic transition curve with an alteration of transition temperatures. The average thermal stability for the nematic mesophase is 153.1°C, and the nematogenic temperature ranges vary from 12°C to 50°C. Analytical data confirm the molecular structures of the homologues. The Liquid Crystal properties and transition temperatures were observed through an optical polarizing microscope, equipped with a heating stage. The mesomorphic characteristics of the novel ester series are compared with other, known and structurally similar series. The novel series is predominantly nematogenic with the absence of any smectogenic character, with relatively short mesophase temperature ranges and of the middle ordered melting type.     

Effects of the Anthraquinone Dye on the Electro-Optical Properties of Dye Guest-Host Polymer Dispersed Ferroelectric Liquid Crystal

Abstract

The effects of the anthraquinone dye on the electro-optical characteristics of DGHPDFLC have been investigated. The results show that PDFLC doped with dichroic dye was found to have no influence on phase separation. When dye concentration is over M483-1.0%, it causes the response time of DGHPDFLC to become slower, the frequency becomes dependent, the rotational viscosity increases, and the tilt angle becomes lower, but, on the whole, electro-optical properties are still very practical.     

Nd3+:d3Ga5O12晶体的室温吸收光谱和荧光光谱

用提拉法生长了掺钕的钆镓石榴石(Nd3+:GG)激光晶体.研究了室温下的吸收光谱和荧光光谱性质,分析了Nd3+:GG晶体4F3/2→4I11/2能级跃迁与1.06μm附近的荧光谱线之间的关系.吸收系数、发射系数、荧光寿命分别是4.32×10-20 cm-2,2.3×10-19cm-2, 240μs, 比较了Nd3+∶GGG 和 Nd3+∶YAG 的物理参数,实验表明:d3+∶GGG较Nd3+∶YAG有一系列的优点.     

Synthesis and Physicochemical Properties of Novel Liquid Crystal Compounds with Negative Dielectric Anisotropy with a Tetrahydropyran Ring: Part 2

With the aim of improving the properties of liquid crystal (LC) mixtures for VA-LCD and PSA-LCD, JNC has newly synthesized 2-(4’-ethoxy-2’,3’-difluorobiphenyl-4-yl)-5-alkenyltetrahydro-2H-pyran derivatives with alkenyl substituents as side chains, and then measured various physicochemical properties to compare their properties to LC compounds with alkyl substituents as side chains. We have shown that several LC compounds with side-chain alkenyl substituents lead to the development of a larger negative dielectric anisotropy (Δ?) than for side-chain alkyl substituents. We considered the reason for this using a quantum chemical calculation. As a result, it was found that, compared to alkylated compounds, there exist several LC compounds with side-chain alkenyl substituents, which have a higher existence probability of conformers with a β angle, making expression of a larger |Δ?| possible in an effective manner. It was understood from this study that the physicochemical properties of LC mixtures for VA-LCD and PSA-LCD, which consist of LC compounds as a structural component, newly developed by JNC, show useful properties.     

Crystal and Molecular Structure of N‐methyl‐N‐3‐(sulfonato)propyl‐3‐[tris(trimethylsiloxanyl)3‐silyl]pyrrolinium Sulfobetaine Hydrate at Room Temperature and 163 K

2 (C₁₇H₄₁NO₆SSi₄) . H₂O. M_r=1017.88, triclinic, space group P‐1. The molecules are arranged in bilayers. The molecules in each bilayer are held together by electrostatic forces, i.e., O‐N⁺ contacts, and hydrogen bonds. The asymmetric unit consists of two partly disordered siloxane molecules and one water molecule. The structure of the bilayers is virtually the same at 163 K and room temperature, but the stacking of the bilayers is different. The Si‐O‐Si bond angles at low temperature are significiantly smaller than at room temperature.