Polymer-stabilized cholesteric liquid crystal microgratings: a comparison of polymer network formation and electro-optic properties for mesogenic and non-mesogenic monomers

Polymer-stabilized liquid crystal microgratings are made using a focused Gaussian UV laser beam to photopolymerize 3 wt % reactive monomer in a cholesteric liquid crystal host. In a typical case, round gratings of 300 μm diameter and 10 μm pitch are produced. The microgratings highlight interesting differences between mesogenic and non-mesogenic monomers in the assembly and spatial distribution of polymer networks formed in a cholesteric host. We also observe a corresponding variation in the electro-optical properties of the stabilized gratings. In the mesogenic case, the grating state of the liquid crystal is faithfully captured even for relatively short UV exposures and over regions only a few pitch lengths in size. These findings are consistent with phase separation of the mesogenic monomer into regular domains templated by periodic, macroscopic variations in orientational order of the host. This templating effect is significantly reduced in the non-mesogenic case.     

Effect of ionic aggregates of sulphonate groups on the liquid crystalline behaviours of liquid crystalline elastomers

A series of siloxane-based liquid crystalline elastomers containing biphenyl benzoate mesogenic units and ionic Brilliant Yellow moieties was synthesized. The chemical structures and liquid crystalline properties of the samples were characterized by FTIR, ¹H NMR, DSC, POM and XRD. The effective crosslink density of the ionic elastomers was determined by swelling experiments in organic/buffer mixtures. All the polymers displayed a smectic mesophase. It was shown that the glass transition and melting point temperatures of the polymers increased slightly with increasing content of ionic and mesogenic groups in the polymers, while the liquid crystal mesophase region decrease slightly.     

Infrared spectroscopic study of a phenyl benzoate side group—methacrylate main chain polymeric liquid crystal

The temperature dependence of the infrared dichroism of a side chain polymeric liquid crystal was investigated for two homogeneously oriented samples, one aligned with a PVA coating and the other aligned by a magnetic field. From the apparent order parameters, it was found that the rotation of the mesogenic side group was restricted. Not only the rigid part of the side group, but also the alkyl chains were found to be partly ordered. Realignment of the side groups was observed in the case of the magnetically aligned sample at the smectic-nematic transition temperature. Unlike the other absorption bands, the C=O bond vibration band shifted to higher wavenumbers with increasing temperature. This behaviour was explained by the influence of the neighbouring mesogenic groups on the conjugation existing between the π-electron cloud of the benzene rings and the π-electrons of the C=O bond.     

Liquid crystalline compounds in the thiophene series. VIII. Synthesis and characterization of liquid crystalline vinylenes with thiophene moieties and carbaldehyde groups

New thermotropic liquid crystal compounds, with one and two mesogenic groups, have been synthesized and characterized. The structural elements of the compounds consist of thiophene ring systems, vinylene units and, for some compounds, carbaldehyde groups. Mesogenic groups involving three thiophene ring systems are normally not liquid crystalline. Only in the case of E,E-5-[5-(5-butyl-2-thienylvinyl)-2-thienylvinyl]-2-thiophenecarbaldehyde could a monotropic nematic phase be easily observed. By replacing thiophene ring systems in the core with a benzene ring system, or by attaching one carbaldehyde group at the moieties, or by doubling the mesogenic groups via an alkylene spacer, the temperature ranges of the mesophases of the compounds with thiophene ring systems can be enlarged or liquid crystal phases induced. The small values for δS_NI, which have been observed for the low molecular weight compounds, indicate a very low order in the nematic phases.     

分子间作用力对咪唑盐介晶相性质的影响

通过对咪唑环1位(N1)取代烷基、3位(N3)取代基及阴离子的修饰合成了一系列具有近晶A (SmA)相的咪唑类离子液晶. 利用差示扫描量热法、单晶衍射、小角度X射线衍射等手段研究了咪唑盐的介晶相温度范围、介晶态的结构, 并测量了部分咪唑盐的各向异性导电率. 结果表明, 咪唑环N1取代烷基、N3取代基及咪唑盐的阴离子会改变分子间范德华力和氢键, 从而对咪唑盐的介晶相性质产生影响. 此外, 当乙烯基引入到咪唑环N3位置时, 咪唑盐相邻的层结构之间形成π-π堆积作用, 不仅有利于介晶态的形成, 同时使氟硼酸类离子液晶具有最大的层间距和最小的各向异性导电率. 这一结果表明, 调控离子液晶的性质时必须综合考虑各种分子间作用力的影响.     

Mesogenic behaviour in some pyrazole and isoxazole derivatives

Several aromatic β-diketones with a different number of alkyloxy groups in the aromatic rings and their derived pyrazoles, isoxazoles and thallium (I) complexes have been synthesized. The potential mesomorphic properties of these compounds have been investigated by optical microscopy, DSC and X-ray diffraction. The pyrazoles and isoxazoles with one chain in each aromatic ring are mesogenic, showing smectic A and smectic C mesophases, whereas the pyrazoles and isoxazoles with two chains per ring and the β-diketones and thallium complexes are not. The mesogenic potentiality is shown to be related to the molecular linearity and to the number of alkyloxy groups. To the best of our knowledge, this is the first time liquid crystal properties have been described for pyrazole and isoxazole derivatives.     

Fast switching anisotropic networks obtained by in situ photopolymerization of liquid crystal molecules

Lightly cross-linked anisotropic networks with uniaxial and π/2 twisted orientations were produced by photopolymerization of monotropic mixtures containing liquid crystal mono and diacrylates. In this way the polymer backbone was immobilized and became decoupled from the motion of the mesogenic side groups. The networks showed very good reversibility and even after becoming isotropic, upon cooling, the initial orientation was recovered. In the same way, in the presence of electric fields the mesogenic groups could be reoriented in the direction of the electric field, reverting back to the initial orientation on removal of the field at a rate comparable with those observed in the monomeric state. Combining viscoelastic measurements with the dielectric behaviour of the monomeric liquid crystal and the anisotropic network, a comparison between the internal and bulk rotational viscosities was also made.     

The synthesis and thermotropic behaviour of an ethyl cellulose derivative containing azobenzene-based mesogenic moieties

An ethyl cellulose derivative containing azobenzene-based mesogenic moieties was prepared by the reaction of 4-methoxyazobenzene-4'-oxyacetic acid and ethyl cellulose by esterification in the presence of N,N' -dicylcohexylcarbodiimide and 4-dimethylaminopyridine. Its chemical structure and liquid crystalline properties were characterized by FTIR, 1 H NMR, POM, DSC and WAXD. The degree of substitution of the cellulose backbone by the azobenzene-based mesogenic moieties is 0.9. The polymer is thermotropic and exhibits liquid crystalline behaviour over the temperature range 125-172°C.     

具有氟烷基边链和手性中心液晶化合物的合成及液晶性研究

本文设计合成了十个含氟烷基边链和手性中心的液晶化合物，并通过DSC和偏光显微镜对它们的液晶性进行了研究。其中二环系液晶化合物不显示液晶相或仅显示单边近晶A相。三环系液晶化合物中较长的氟烷基边链有利于近晶相的形成，且当液晶核另一端的烷氧基链的长度适中时，在氟烷基边链和液晶核之间具有手性中心的液晶分子显示了手性近晶C相和其它液晶相。     

The synthesis and thermotropic behaviour of an ethyl cellulose derivative containing azobenzene-based mesogenic moieties

An ethyl cellulose derivative containing azobenzene-based mesogenic moieties was prepared by the reaction of 4-methoxyazobenzene-4′-oxyacetic acid and ethyl cellulose by esterification in the presence of N,N′ -dicylcohexylcarbodiimide and 4-dimethylaminopyridine. Its chemical structure and liquid crystalline properties were characterized by FTIR, ¹H NMR, POM, DSC and WAXD. The degree of substitution of the cellulose backbone by the azobenzene-based mesogenic moieties is 0.9. The polymer is thermotropic and exhibits liquid crystalline behaviour over the temperature range 125–172°C.     

Non-conventional multi-arm ester liquid crystal derived from cholic acid: synthesis,thermal and optical behaviour

ABSTRACT

With cholic acid as the core, five multi-arm ester liquid crystals were synthesised with different terminal substituents. B₁–B₅ were mesogenic arms which were linked to multifunctional chiral core cholic acid. The effect of electron-withdrawing and electron-donating groups on the mesogenic behaviour of the compounds was discussed. All products were structurally well characterised by elemental analysis, ¹HNMR, and FT-IR. The phase behaviours were investigated by means of polarised optical microscopy and differential scanning calorimetry. B₂, B₄, B₅ and C₂, C₄, C₅ and D₂, D₄, D₅ exhibited typical nematic texture and belonged to thermotropic enantiotropic nematic liquid crystals. B₃, C₃ and D₃ also displayed typical nematic texture of thermotropic monotropic nematic liquid crystal. B₁, C₁ and D₁ did not have mesogenic performance. Wider mesogenic range for 81.6°C of C₅ whose terminal substituent is nitro on heating cycle while 121.1°C on cooling cycle. The results indicated that terminal substituents have a pretty important effect on the mesogenic phase and range of multi-arm liquid crystal compounds. The mesomorphic behaviour of compounds with polar groups terminally substituted performance much better than those without polar groups. In this ester multi-arm liquid crystal system, electron-withdrawing groups terminally substituted behave better than those electron-donating groups substituted.     

Liquid crystal oligomers: going beyond dimers

This review focuses on structure-property relationships in liquid crystal oligomers, which consist of molecules containing two or more mesogenic units linked via flexible spacers essentially in a linear fashion and so does not consider, for example, liquid crystal dendrimers and tetrapodes. Previous reviews have tended to focus mainly on liquid crystal dimers in which just two mesogenic units are interconnected by a single spacer. By contrast, this review is largely devoted to higher oligomers such as liquid crystal trimers and tetramers containing three or four mesogenic units connected by two or three spacers, respectively.     

Thermal properties and ionic conductivity of a polymer prepared by the in situ photopolymerization of a vinylimidazole monomer containing a mesogenic group

We have synthesized liquid crystalline polymers containing an imidazolium salt moiety and a mesogenic group by the in situ photopolymerization of a liquid crystalline vinylimidazole monomer in order to investigate the relationship between their thermal properties and ionic conductivity. A smectic phase was shown by the vinylimidazole monomer. The in situ photopolymerization of the monomer was carried out in the temperature range of the smectic phase. The polymer thus prepared displayed a highly ordered smectic phase in the temperature range between room temperature and about 200°C. The ionic conductivity of the polymer increased with increasing temperature. Anisotropic ionic conductivity behavior was observed for the polymer. The ionic conductivity of the polymer aligned homogeneously is larger than when homeotropically aligned.     

含两种不同介晶基团的半刚性共聚酯液晶态的结构研究

用Ｘ－光衍射，偏光显微镜及ＤＳＣ对含两种不同长度介晶基团４，４’－联苯二酚（Ⅰ）和对苯二甲酸二（对羟苯基）酯（Ⅱ）的系列共聚酯的液晶态进行了表征，据其液晶态中两种介晶单元的堆砌方式提出了可能的模型，这种模型很好地解释了液晶态的Ｘ－光衍射分布．     

离子液体(1-甲基-3-羧甲基咪唑)钴配合物的合成和晶体结构

由离子液体1-甲基-3-羧甲基咪唑硫酸氢盐([C6H9N2O2][HSO4])和氯化钴合成了一种新的配合物[Co(H2O)4(C6H8N2O2)2]Cl2.2H2O;采用单晶X射线衍射方法测定了配合物的晶体结构.结果表明,所合成的配合物C12H28Cl2CoN4O10属于三斜晶系,空间群P-1,a=0.66753(5)nm,b=0.91751(6)nm,c=1.80604(13)nm,α=85.618(5)°,β=83.385(5)°,γ=83.443(5)°,V=1.08934(13)nm3,Z=2,Mr=520.23,F(000)=538,Dc=1.580g.cm-3,μ(Mo-Kα)=1.088mm-1,R1=0.0861,wR2=0.2878.单晶X射线分析结果表明,在所合成的配合物中,每个1-甲基-3-羧甲基咪唑除羧基外其它原子均位于同一平面,咪唑环带正电荷,而羧基氢原子消失;即整个1-甲基-3-羧甲基咪唑分子不带电荷.总体而言,配合物的内界[Co(H2O)4(C6H8N2O2)2]2+带两个正电荷,外界游离的两个氯离子起平衡电荷作用.     

Mesomorphism of ionic allylpalladium(II) complexes containing pz(R2)py as ligands and [BF4]-, [PF6]- or [CF3SO3]- as counteranions

The synthesis and thermal behaviour is reported of some ionic liquid-crystalline complexes formed when a mesogenic, two-chained, pyrazolylpyridine ligand is bound to a eta3-allylpalladium(II) fragment. The phase behaviour of the complexes is dominated by the formation of the SmA phase and, while the stability of the crystal phase appears to be controlled by intermolecular solid-state interactions, the stability of the liquid crystal phases is controlled by the length of the ligand alkoxy chains. Some of the complexes also show a complex polymorphism leading to the observation of double-melting behaviour.     

液晶基元直接横挂于主链上的液晶共聚物研究

以含有液晶基元的单体，２，５－双（４－甲氧基苯甲酰氧基）苯乙烯与丙烯醇，通过自由基共聚合反应，首次合成了一系列含液晶性单体和非液晶性单体两种结构的共聚物．采用ＤＳＣ、偏光显微镜和Ｘ－衍射方法研究了共聚物的液晶行为，发现单体和所有的共聚物均有明显的热致液晶性及较宽的液晶态温度范围；随共聚物中液晶性单体含量增加，共聚物玻璃化转变温度Ｔｇ和热分解温度Ｔｄ有所上升，但Ｔｇ的变化较小．     

Voltage‐Driven Photoluminescence Modulation of Liquid‐Crystalline Hybridized ZnO Nanoparticles

Liquid‐crystalline hybrid nanomaterials have been obtained by grafting mesogenic units around luminescent ZnO nanocrystals of 5 nm in diameter. Modifying the mesogenic density around the inorganic core allows the modulation of the liquid‐crystalline behavior and its miscibility in commercial liquid crystal (LC). The strong blue photoluminescence observed for the hybrids can be modulated by applying a voltage on a LC cell containing commercial LC and 10 wt % of hybrid.     

Heterotrimeric liquid crystalline thiadiazole derivatives

Abstract

Various trimeric co-oligomers combining 2-phenyl-1,3,4-thiadiazole mesogenic moieties with a biphenyl mesogenic moiety were synthesized and their mesomorphic behaviour investigated by polarizing microscopy, calorimetry and X-ray scattering. Such co-oligomeric structures provide an opportunity to combine different mesogenic units. Thus readily accessible homochiral biphenyl mesogenic units were connected with thiadiazole mesogenic units leading to an oligomeric liquid crystal material with ferroelectric properties.     

Variation of molecular stacking with different length of alkyl chain: synthesis,structure determination,and mesogenic study of N,N‐disubstituted aminophenylazo‐(4)‐p‐alkylbenzenes

To help understand the influence of polarity and length of the terminal alkyl chain of a molecule on the molecular stacking of a liquid crystal and on its mesogenic behaviour, four new aminophenylazo‐(4)‐p‐alkylbenzenes were prepared and one of them was further studied by single crystal structure determination. The molecular stacking based on this crystallographic data was established, and compared with that of two previously reported homologues. The mesogenic behaviour of this series of compounds was also investigated.