Synthesis and photochemistry of side-chain liquid crystal polymers based on cinnamate esters

The syntheses of three methacrylate monomers with cinnamate ester side-chains and of a further monomer with a corresponding cinnamide side-chain are described. Two of the monomers, with isomeric structures, were thermotropic liquid crystals. Although the clearing points were very similar the crystal melting points differed by 8°C. One compound also exhibited a monotropic smectic phase, behavior not shown by its isomer. The other two monomers were not liquid crystalline. The monomers were polymerized by free radical polymerization, both as homopolymers and as copolymers with methyl methacrylate. In the case of one of the mesogenic ester monomers, copolymers with a cyanophenyl benzoate monomer were also prepared. Three of the four monomers formed thermotropic liquid crystalline homopolymers and the copolymers with the benzoate monomer were also liquid crystalline. The monomers were considered as photoactive components of polymeric liquid crystals. As a preliminary investigation of their photochemistry, copolymers with methyl methacrylate were prepared and irradiated in solution with a broad-band source. Under these conditions two of the materials show a facile photo-Fries rearrangement of the aryl cinnamate ester group. © 1992 John Wiley & Sons, Inc.     

Small-angle X-ray scattering study of liquid crystalline polycarbonates based on α-methyl stilbene mesogen and methylene-containing flexible spacer

Crystallization and melting behavior are studied by small-angle X-ray scattering (SAXS) for a series of recently synthesized monotropic liquid crystalline polycarbonates based on α-methyl stilbene mesogen and methylene flexible spacer. The one-dimensional electron density correlation function is used to obtain long period, crystal thickness, and linear crystallinity from the Lorentz-corrected SAXS intensity. Changes in these parameters during nonisothermal crystallization and melting are explained by a model of dual crystal populations. The primary crystals form first using the liquid crystalline phase as crystal nuclei, while smaller and less perfect crystals form later from the isotropic phase at low temperature. The results of the real-time SAXS study of isothermal crystallization also support the view that the nematic phase serves as crystal nuclei for fast crystallization. An odd-even effect in crystal thickness and linear crystallinity is observed in all the SAXS experiments mentioned above. The results of this study and our complementary wide-angle X-ray scattering (WAXS) investigation show clearly that the difference in the position of the neighboring carbonate dipoles on a chain affects structural organization both at the unit cell level and at the level of the crystal in these monotropic LCPs. © 1995 John Wiley & Sons, Inc.     

Reentrant 2D Nanostructured Liquid Crystals by Competition between Molecular Packing and Conformation: Potential Design for Multistep Switching of Ionic Conductivity

Reentrant phenomena in soft matter and biosystems have attracted considerable attention because their properties are closely related to high functionality. Here, we report a combined experimental and computational study on the self-assembly and reentrant behavior of a single-component thermotropic smectic liquid crystal toward the realization of dynamically functional materials. We have designed and synthesized a mesogenic molecule consisting of an alicyclic trans,trans-bicyclohexyl mesogen and a polar cyclic carbonate group connected by a flexible tetra(oxyethylene) spacer. The molecule exhibits an unprecedented sequence of layered smectic phases, in the order: smectic A-smectic B-reentrant smectic A. Electron density profiles and large-scale molecular dynamics simulations indicate that competition between the stacking of bicyclohexyl mesogens and the conformational flexibility of tetra(oxyethylene) chains induces this unusual reentrant behavior. Ion-conductive reentrant liquid-crystalline materials have been developed, which undergo the multistep conductivity changes in response to temperature. The reentrant liquid crystals have potential as new mesogenic materials exhibiting switching functions.     

刚性链侧链型液晶高分子合成与研究

以自由基聚合方法，合成了一系列含有３个苯环通过酯键相联的液晶性单体及其聚合物，这类刚性液晶基元不通过柔性间隔基而直接竖挂在聚丙烯酸酯大分子主链上，具有很高的Ｔｇ·ＤＳＣ及偏光显微镜结果表明，所有的单体和聚合物均为向列型热致性液晶。     

新的手性Schiff碱液晶的合成及变温红外光谱研究(Ⅰ)

合成了1个新的手性Schiff碱类液晶并以DSC、偏光显微镜及变温红外光谱等手段对其热致相变过程进行了研究。     

基于核酸和蛋白的生物大分子热致液晶研究进展

生物固体大分子诸如核酸、蛋白和病毒颗粒,因其尺寸超出了分子间作用力的范围,升温之后会导致它们降解而无法形成生物大分子的液体形态。 因此,发展新型的合成和制备策略,实现无溶剂包覆的生物大分子的流体态及其应用,是一个崭新的研究领域。 结合我们前期工作,简要介绍了核酸、蛋白流体(液晶态和液体态)材料的制备及性质。 借助静电力自组装,上述生物大分子能够与带有相反电荷的表面活性剂结合,形成热致液晶材料,其热致液晶性质使得生物分子具有长程有序性和流动性,在此基础上,可以探索生物大分子在无水环境下的技术应用。     

Synthesis and characterization of polymerizable β-diketone-based liquid crystalline metal chelates

Two novel square-planar palladium chelating liquid crystals, bis(p-n-(l-undecenoxyphenyl-3-dodecyloxyphenyl)-propane-1,3-dionato)palladium(II) (Pd-C₁₁-C₁₂) and bis(1,3-di(p-n-tetradecyloxphenyl)-propane-1,3-dionato) palladium (II) (Pd-C₁₄-C₁₄) have been synthesized. Moreover, the copper chelating liquid crystal bis(p-n-(l-undecynoxylphenyl-3-dodecyloxylphenyl)-propane-1,3-dionate)copper (II) (Cu-Cu₁₁-C₁₂) has been synthesized by heterogeneous ligand-exchange reaction. These β-diketone metal chelates have been characterized by elementary analysis, differential scanning calorimetry, polarizing microscopy, X-ray diffraction analysis and temperature-variable IR. It was found that these chelates were discotic lamellar-(D_L) mesophase liquid crystals. In particular, the temperature-variable IR study indicates that the central chelating ring and the surrounding benzene rings would form a co-planar conjugated structure in the liquid crystalline (LC) state.     

1-烷基-3-甲基咪唑溴化盐离子液体的晶体结构及性能

以不同链长溴代烷烃和N-甲基咪唑反应得到1-烷基-3-甲基咪唑溴化盐,用元素分析和核磁共振对化合物进行了表征.室温下用溶剂蒸发法得到了单晶,并用X射线单晶衍射法测定了晶体结构,该晶体属于三斜晶系,空间群为P-1.化合物采用双分子层结构,水分子参与结构的形成,整个化合物由交叉的线性烷基链、咪唑头基、溴离子和水分子组成,溴离子和水分子之间较强的氢键作用在(010)方向上形成了一个无限的O-H···Br氢键链.用偏光显微镜、差示扫描量热(DSC)技术研究了其液晶行为,证明其一水合物为近晶相热致液晶.液晶区域的温度范围较宽说明水分子起到稳定作用.     

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．     

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．     

Mesogen-jacketed Liquid Crystal Polymers With Mesogens of Aromatic Amide Structure

The synthesis and property of a new series of "mesogen-jacketed liquid crystal polymers" are reported. These polymers have aromatic amide structures as the mesogenic groups and are represented by poly-2,5-bis(4-methoxy- benzamido)styrene. The preliminary study on properties shows that the polymers have very high glass transition temperatures as well as very low critical concentrations for the formation of the lyotropic liquid crystal phase. The results indicate a high degree of chain rigidity. However, the liquid crystalline order of molecular organization in bulk samples disappears upon heating to the glass transition temperature as revealed by polarizing microscopy and by X-ray diffractometer. Therefore, the liquid crystalline order of these polymers forms only through solution but not through heating. This behavior is different from that of the previously studied poly-2,5-bis[(4-methoxybenzoyl)oxy]styrene and its homologs. The latter polymers are liquid crystals both lyotropically and thermotropically. © 1997 John Wiley & Sons, Ltd.     

液晶性芳香酰胺化合物的合成

合成了一系列炖粹以酰胺基为中心桥键的刚性芳香酰胺小分子化合物，并对其作了表征，发现其中有些化合物具有液晶性。酰胺键之间能形成很强的分子间氢键，使芳香酰胺小分子化合物的熔点很高，难于形成液成液晶态。研究发现，如果在这类化合物的中心苯环上引入合适的取代基以减弱分子间氢键，同时引入合适的末端基时，则可使芳香酰胺化合物生成液晶相的能力增强。     

Crystallization behavior of polyethers containing odd numbers of methylene spacers from the isotropic and liquid crystalline states

A series of thermotropic polyethers synthesized from 1-(4-hydroxyphenyl) - 2 - (2 - methyl - 4 - hydroxyphenyl) - ethane and α,ω-dibromo-n-alkanes with odd numbers of methylene units (MBPE-n = odd) shows monotropic mesophase behavior. In isothermal differential scanning calorimetry (DSC) experiments, two—sometimes even three—exothermic transition processes can be observed when the crystallization temperature is below the mesophase transition temperature, while only one exothermic process is present above the mesophase transition temperature. The melting behavior of the crystals grown from the mesophase and from the isotropic melt states is different. The crystals grown from the mesophase state exhibit a larger overall heat of transition and a higher transition temperature compared with those grown from the isotropic melt. This may be attributed to the molecular interfacial connections between the crystal and amorphous regions when MBPEs crystallize from the mesophase state. The difference in morphology between the crystals grown from the different states has also been studied with polarized light microscopy (PLM) and transmission electronic microscopy (TEM). The structures of the crystals grown from the different states are, however, the same, as evidenced through wide-angle X-ray diffraction (WAXD) measurements. From the banded morphology of MBPE samples observed from PLM, the defect textures observed through TEM and the results of WAXD experiments, this mesophase can be identified as a nematic liquid crystal state.     

Benzoate liquid crystals with direct isotropic–smectic transition and antipathogenic activity

A smectogen liquid crystal based on benzoate units has been synthesized and structurally characterized by FTIR and ¹H NMR spectroscopy. Besides, its structure and supramolecular arrangement in the crystalline state was demonstrated by single crystal X-ray diffraction measurements. The thermotropic behaviour, monitored by differential scanning calorimetry and polarized light microscopy, consists in the formation of an enantiotropic smectic mesophase with a direct first order transition from the isotropic to smectic mesophase, and with its thermal stability range superposed on human body temperature. The smectogen liquid crystal has moderate wettability – suitable for biocompatible materials and presents good antipathogenic activity against gram positive and gram negative bacteria and fungus.All these properties recommend the understudied liquid crystal to be used in biochemical and biological applications.     

meso-四(邻烷氧基苯基)卟啉合锌的合成、表征和性能研究

用邻烷氧基苯甲醛与吡咯缩合合成meso-四(邻烷氧基苯基)卟啉, 再与醋酸锌配合反应合成了meso-四(邻烷氧基苯基)卟啉合锌配合物10个, 其中未见文献报道的配合物9个, 得到该系列配合物的晶体或固体. 用¹H NMR, MS, IR, UV, 元素分析等表征确证了该系列配合物的结构. 用差示扫描量热法和偏光显微镜研究了该系列配合物的液晶性能, 发现6个配合物具有液晶性, 其液晶行为表现为升温单变液晶.     

Insight into Out-of-Layer Fluctuations in the Smectic A Stability of 3,5-Diarylisoxazole Liquid Crystals

Polar-terminated 3,5-diarylisoxazole liquid crystals (ILCs) were synthetized and characterized. ILCs are composed by rigid core 3,5-diarylisoxazol, alkyl chain and polar-terminated flexible spacer. Hydroxyl-, ketal- and 1,2-diol-terminated ILCs rendered smectic C and A mesophase, while bromine-terminated ILCs showed smectic A and B mesophase, for monosubstituted and linear ILCs. For branched alkyl chain monotropic SmA was detected and for disubstituted ILCs no mesophase was detected. Out-of-layer fluctuations (OLFs) are discussed based on X-ray diffraction date and textures. The OLFs are dependent on the bromine atom hardness, hydrogen bonding through collective actions and conformational effects at the interface between layers. Smectic translational order parameter (TOP) Σ was also obtained for orientated bromine- and hydroxyl-terminated ILCs and related it with OLFs. For 1,2-diol-terminated ILCs two SmC sublayers were founded, probably related to the intramolecular hydrogen bond favoring the 5-membered and 6-membered formation.     

Synthesis and liquid crystal properties of copper(II) and palladium(II) chelates with new ferrocene-containing enaminoketones

Heterometallic liquid crystals are of special interest because of the possibility to combine optical, magnetic and electric properties of different metal ions in one mesogenic molecule. In order to investigate new heteropolynuclear mesogenic systems, a series of β-aminovinylketone ligands derived from acetyl ferrocene have been synthesized. Subsequently Cu(II) and Pd(II) ions were incorporated into the enaminoketone chelate core. The obtained ligands and complexes were characterized by element analysis, ¹H NMR, IR and UV–Vis spectroscopies. According to thermal polarizing microscopy and DSC studies, the ligands and Cu(II) complexes exhibit disordered soft crystal phases upon cooling from the isotropic liquid state. The Pd(II) complexes showed monotropic smectic C mesomorphism. The metal centres in the synthesized heteropolynuclear mesogens are in close vicinity to each other, which is of considerable interest from the viewpoint of the potential electron-transfer interactions between a ferrocene core and the central ions.     

A study of the transition of liquid-crystal alignment from homeotropic to planar on a polyimide layer

The alignment of nematic liquid crystals by rubbed polyimide surfaces has been well-studied and developed. A novel polyimide film which induced a homeotropic alignment of the nematic liquid crystal without rubbing or with weak rubbing strength was presented. However, there was a transition from homeotropic to planar alignment of the nematic liquid crystal after strong rubbing. In order to study the transition, the polyimide surface was investigated by atomic force microscopy, surface free energy measurement and angle-resolved analysis X-ray photo-electron spectroscopy before and after rubbing with a velvet fabric. It was found that both the change of surface polarity and surface morphology were not the reasons for the transition. The droop of the side chain on the polyimide surface after the rubbing treatment was detected by angle-resolved analysis X-ray photo-electron spectroscopy. Owing to the special structure of the novel polyimide, the X-ray photo-electron spectroscopy was successfully used for the first time to analyse the conformational change of the side chain of a polymer. In conclusion, the transition of nematic liquid crystal alignment from homeotropic to planar after rubbing was influenced by the side chain conformation of the polyimide.     

Transitions of bipolar to radial orientation of liquid crystal droplets in amphiphilic system of PDLC film

The orientation order of nanoscale droplets of thermotropic liquid crystals (LCs) suspended in polymer dispersed liquid crystal (PDLC) solutions prepared with different medias (e.g., polymers, surfactants, nonpolar materials like dyes) respond sensitively and differently via molecular interactions. Such a valuable knowledge provides basis for understanding the properties of PDLC devices. Previously, many studies have explored the droplets size, electro-optical property variations in PDLC films by varying the materials types and its compositions. However, the variations in droplet orientation order with respect to material type and composition provide a new class of study in this particular field. The current study explored the transition in droplet orientation from bipolar to radial on varying the amphiphilic block copolymer concentrations. Further, the variations in surface energies of LCs in different series of block copolymer medias were investigated by contact angle measurements.     

New insights into the transitional behaviour of methyl-6-O-(n-dodecanoyl)-α-D-glucopyranoside using variable temperature FTIR spectroscopy and X-ray diffraction

The liquid crystalline behaviour of methyl-6-O-(n-dodecanoyl)-α-D-glucopyranoside, 1, has been characterised using X-ray diffraction and variable temperature Fourier transform infrared (FTIR spectroscopy). 1 exhibits a monotropic interdigitated smectic A phase consisting of bilayers in which the alkyl chains are overlapped. The crystal–isotropic transition is accompanied by a pronounced decrease in the strength of the hydrogen bonding network involving the sugar groups resulting in a marked change in the environment of the alkyl chains. The isotropic phase consists of disordered smectic-like domains stabilised via hydrogen bonding between the sugar groups. At the transition to the smectic A phase, a subtle change in hydrogen bonding is observed which is manifested by a change in the temperature dependence of the OH stretching peak position in the FTIR spectrum. On crystallisation, the strong hydrogen bonding network is re-established accompanied by a change in the conformational distribution of the alkyl chains. A model is proposed in which a combination of hydrogen bonding (enthalpic effects) and conformational arrangements (entropic effects) promotes initially the formation of smectic-like domains in the isotropic phase and subsequently stabilises the smectic A phase by inhibiting the microphase separation leading to the crystal phase.