氢键超分子液晶聚合物的研究进展

超分子液晶是利用弱键相互作用构筑的多种超分子液晶复合体系,因具有动态可逆性而被广泛研究。本文在介绍超分子液晶概念的基础上,对氢键超分子液晶聚合物的分类作了简述,重点总结了氢键超分子液晶聚合物的研究进展。     

聚乙烯醇侧链液晶的结构与液晶性研究

研究了聚乙烯醇侧链液晶主链分子量和液晶基元等结构因素对其液晶性的影响，结果表明随着聚合物的分子量增加，导致复合物清亮点温度下降。但是在液晶主链尚未被液晶基元饱和之前，随着液晶基元相对主链摩尔比的增加，样品形成较为完善的氢键结构。     

分子间氢键自组装手性液晶的变温红外研究(英文)

通过存在于吡啶环和羧基间的分子间氢键自组装合成液晶已逐渐引起科学工作者的重视,决定这种方法是否适用的关键是分子间氢键的稳定性。由于变温红外光谱能很好地反映出液晶分子环境的变化,尤其是分子中羰基基团对分子环境变化,对分子内和分子间的相互作用更为敏感,并且又能反映出这种分子间氢键的稳定性。因此本文研究了通过存在于4—[(2S)—2—氯—3—甲基—丁酰氧基]—4′—苯乙烯基吡啶(MBSB)和4—烷氧基苯甲酸(nBA,n=5,6)问的分子间氢键自组装的两个手性液晶(nBA:MBSB)的变温红外光谱。研究结果表明nBA:MBSB中的酯羰基基团对于K—Sc*转变极为敏感,对Sc*—S_A和S_A—N转变不敏感,同时结果表明分子间氢键在晶体和液晶态是稳定的,并且这种分子间氢键强于存在于羧基和羧基间的氢键,因此这种存在于羧基和吡啶环间的氢键为液晶分子设计提供了又一条有效的途径。     

基于分子间氢键的棒状手性液晶的研究进展

分子间氢键棒状手性液晶因其兼具手性液晶奇特的光电性能和氢键液晶的便捷制备以及独特的外界刺激响应性,在功能材料、非线性光学、生物医学等领域具有潜在的应用价值,一直是超分子液晶领域的研究热点。文章按照形成氢键互补基团的不同,将其划分为3种类型,即羧酸-羧酸类、羧酸-吡啶类和其他类型氢键,介绍了此三类氢键棒状手性液晶近年来的研究进展。详细归纳了氢键质子给受体的分子结构、氢键稳定性、手性中心位置、取代基、柔性链长度等对液晶性能的影响,并在此基础上,对其未来发展做了展望。     

可交联型两性双亲分子的合成及其溶致液晶相结构的研究

本文报道了一种可交联型的两性双亲分子的设计及合成路线,并进一步探究了其溶致液晶相态。以1,10-二溴代癸烷、丙二酸二乙酯为原料,在液晶分子烷基链末端引入两个可聚合甲基丙烯酸酯基官能团,再通过与1,3-丙烷磺酸内酯的季铵化反应合成了可聚合型两性离子液晶基元。通过核磁共振波谱(NMR)确定合成目标产物的化学结构。运用偏光显微镜(POM)表征并分析了该分子在水中的溶致液晶相行为。根据临界堆积参数(Critical Packing Parameter)推测,该分子临界堆积参数CPP介于1/2～1之间,与水共混自组装易于形成层状相。     

氢键诱导胆甾相液晶化合物的合成(英文)

本文通过存在于胆甾醇丁二酸单酯(MCB)和4—(4—烷氧基苯甲酰氧基)—4′—苯乙烯基吡啶(nSZ)间的氢键作用合成了一系列新的胆甾型液晶,其液晶行为通过DSC、偏光显徽镜及变温广角X光衍射等手段进行研究。对于nSZ:当n≤3时,仅呈现向列相;当n=4,5时,呈现近品A相和向列相;当n＝6,7时,还出现一种单变的近晶相(S相);当n≥8时,向列相不存在,只呈现近晶A相和单变的S_1相。MCB不是液晶,而两者的1:1复合物均呈现互变的近晶C相和胆甾相,并且当n≤3时,nSZ:MCB的相变区间比nSZ的相变区间宽。X光衍射结果表明,7SZ扣8SZ的层厚度(d值)比基分子全伸展理论长度要长,这意味着这种不含强极性基团(如硝基、氰基)的液晶分子呈双层排列。     

基于异烟酸酯类衍生物的超分子盘状液晶构建

将异烟酸酯类棒状小分子代替苯乙烯基吡啶作为质子受体;与对称型盘状质子供体间苯三酚形成了氢键复合超分子盘状液晶结构。通过红外光谱和变温红外光谱表征了氢键的存在及稳定性,并通过POM和DSC研究了复合体系的相转变行为,通过变温XRD详细表征了中间相结构。研究表明,酯键代替乙烯基链接键能够在不影响分子间氢键稳定性的情况下降低体系的有序度,从而得到有序度较低的盘状向列相中间相。     

氢键复合物中间相行为的变温红外光谱研究

在差示扫描量热仪(DSC)和偏光显微镜(POM)的辅助下,采用变温红外光谱对所制备的基于4,4′-联吡啶(BPy)和4-丙基苯甲酸(PBA)、4-丙基反式环己基甲酸(PCA)的氢键超分子复合物PBA-BPy和PCA-BPy中的氢键的热稳定性进行了研究.结果表明,超分子PBA-BPy中的氢键非常稳定,甚至在温度高于它的清亮点时氢键也不分解;而对于PCA-BPy,情况则完全不同,当温度稍高于它的熔点时,其分子中的氢键就被破坏.这一结果解释了为什么在结构类似的情况下PBA-BPy具有近晶相和向列相行为而PCA-BPy不具有任何中间相特征.     

新型二元胆甾相液晶的超分子自组装比较研究

在21世纪,液晶具有良好的动力学性质,将成为非常重要的功能性材料。它对各种刺激和环境较为敏感,因此新型液晶材料有待开发。本文以胆甾醇和丁二酸酐为原料合成了丁二酸单胆甾醇酯(AC),研究探讨了AC自组装液晶特性;AC与4,4′联吡啶通过氢键自组装形成丁二酸单胆甾醇酯与4,4′联吡啶的复合物(ACBP);AC与对胺基联苯反应得到了丁酸4,4′-([1,1'-苯基]-4,4′亚胺)-双-[4-氧-双胆甾醇酯](CBC),并进一步利用FTIR和ESI质谱等方法表征了自组装体的形成,利用DSC和偏光显微镜探讨了它们的液晶性质。展示了如何组装成超分子液晶。说明液晶分子的组装方式与胆甾相液晶的形成没有直接关系,而组装后的分子形状是其形成有序排列的决定因素。讨论了胆甾醇衍生物氢键液晶和共价液晶的不同性质,因而它们可以作为潜在的光学材料应用于实际生活中。     

环己烷类聚硅氧烷侧链液晶的合成与液晶行为研究

选用环己烷类液晶基元反式-4-乙烯基-反式-4’-丙基双环己烷(MA)和反式-4-丁烯基-反式-4’-丙基双环己烷(MB),通过硅氢加成反应将其接枝到柔性的聚硅氧烷主链上,合成了含有2种环己烷结构的聚硅氧烷侧链液晶P_(AB),产率为80.3%。采用傅立叶变换红外光谱法(FTIR)和氢核磁共振谱法(~1H-NMR)对其分子结构进行表征,说明其分子结构符合预期;采用热台偏光显微镜法(POM)和X射线衍射法(XRD)对其液晶相类型和液晶行为进行观察和分析,发现在升降温过程中所呈现出胆甾相油状条纹织构和小板块织构,揭示出因有序度不同所导致的不同织构特征;采用差示扫描量热法(DSC)和综合热分析法(TGA)对其热性能进行分析,确定其液晶区间为28.68K,T_(d(5wt%))为405.25℃,均高于液晶基元的液晶区间和热稳定性。     

Preparation of poly (N-vinylcarbazole)-co-poly(2-(dimethylamino)ethyl methacrylate) based hydrogen bonded side-chain liquid crystal copolymer

In this study, new side chain liquid crystalline copolymers were prepared from N-vinyl carbazole (NVC) and 2-(Dimethylamino)ethyl methacrylate) (DMAEM) as a hydrogen bond acceptor copolymer and 8-(4-cyanobiphenyl-4′-oxy)octan-1-ol (LC8) by molecular self-assembly processes via hydrogen bond formation between nitrogen of (DMAEM) and hydroxyl group of the LC8. The formation of H bond was confirmed by using FTIR spectroscopy. The liquid crystalline behavior of the copolymers and homopolymer of the (DMAEM) was investigated using a differential scanning calorimeter (DSC) and polarized optical microscopy. The dielectric relaxation properties of H-bonded Side Chain LC Copolymers (HB-LCP) doped 8-(4-cyanobiphenyl-4′-oxy)octan-1-ol (LC8) and pure LC8 liquid crystals have been investigated by the dielectric spectroscopy (DS) method. The dielectric behavior of the LCs shows a dielectric relaxation process. The relaxation frequency of the LCs was changed by the addition of HB-PLC. It is evaluated that the dielectric strength and relaxation properties of LC8 and LC8/HB-PLC LCs can be controlled by 1% HB-PLC dopant.     

异硫氰基嘧啶乙炔类液晶合成及性能研究

中心环外侧嘧啶环作为液晶分子的极性介晶基团,能有效增大分子的偶极矩和分子间的作用力,提高分子的介电各向异性,降低液晶的驱动电压,也有利于形成近晶相液晶态。本文试图以嘧啶乙炔为中心结构单元,以异硫氰基为端基,设计合成了嘧啶乙炔类异硫氰基液晶化合物(nBTM-NCS)系列共5个化合物;它们都经过IR、~1H-NMR、~(13)C-NMR和MS光谱对其分子结构鉴定,经过差热分析仪(DSC)和偏光显微镜(POM)对其液晶性能进行检测。实验结果表明,所有化合物的分子结构均正确,具有近晶相态,其熔点较高并呈现奇偶效应;其光学各向异性达到0.45左右,介电常数21~24左右,可作为铁电液晶和聚合物分散液晶材料配方组分。     

乙炔桥键四环异硫氰酸酯液晶化合物的合成及性能

为了研究液晶材料结构与性能的关系,本文以含乙炔桥键的四环异硫氰酸酯化合物为研究对象,芳基硼酸和3-氟-4-溴碘苯为起始原料,经6步反应合成了12种目标化合物,LC纯度大于99%,采用核磁共振、红外光谱对其结构进行了表征。采用DSC和POM对目标化合物的介晶性进行了研究,采用外推法对其双折射率和介电各向异性值进行了测试。结果表明:目标化合物具有300℃以上高清亮点、150℃以上向列相温度区间、0.40~0.51的双折射率以及大于17的介电各向异性值。对于同一系列化合物,随着末端烷基链的增长,化合物熔点降低,但呈现近晶相的趋势增加。在Y、Z位引入侧向氟取代基,熔点和清亮点均降低;X位再引入侧向氟取代基,熔点上升、清亮点下降。用环己烷替代左边第一个苯环,化合物熔点降低、向列相温度区间变宽。引入侧向氟取代基使双折射率下降0.008~0.036。目标化合物有利于提高混合液晶配方的双折射率、清亮点和降低阈值电压。     

Liquid Crystal Enabled Early Stage Detection of Beta Amyloid Formation on Lipid Monolayers

Liquid crystals (LCs) can serve as sensitive reporters of interfacial events, and this property has been used for sensing of synthetic or biological toxins. Here it is demonstrated that LCs can distinguish distinct molecular motifs and exhibit a specific response to beta‐sheet structures. That property is used to detect the formation of highly toxic protofibrils involved in neurodegenerative diseases, where it is crucial to develop methods that probe the early‐stage aggregation of amyloidogenic peptides in the vicinity of biological membranes. In the proposed method, the amyloid fibrils formed at the lipid–decorated LC interface can change the orientation of LCs and form elongated and branched structures that are amplified by the mesogenic medium; however, nonamyloidogenic peptides form ellipsoidal domains of tilted LCs. Moreover, a theoretical and computational analysis is used to reveal the underlying structure of the LC, thereby providing a detailed molecular‐level view of the interactions and mechanisms responsible for such motifs. The corresponding signatures can be detected at nanomolar concentrations of peptide by polarized light microscopy and much earlier than the ones that can be identified by fluorescence‐based techniques. As such, it offers the potential for early diagnoses of neurodegenerative diseases and for facile testing of inhibitors of amyloid formation.     

Photogeneration of High Pretilt Angles of Nematic Liquid Crystals by Non‐Polarized Light Irradiation of Azobenzene‐Containing Polymer Films

A vertical‐alignment (VA) cell of nematic liquid crystals (LCs) was prepared using photoirradiated thin films of a poly(methacrylate) with mesogenic moieties of 4‐trifluoromethoxyazobenzene as the side chains. Optical anisotropy was generated by oblique irradiation of the azobenzene‐containing polymer films with non‐polarized UV light, followed by annealing treatment to enhance the photodichroism, which displayed thermal stability. The combination of oblique exposure to non‐polarized UV light and subsequent annealing treatment brought about high pretilt angles of nematic LCs so that a photoaligned VA LC cell was fabricated. The photopatterned LC cell exhibited electro‐optical properties with excellent optical quality when a voltage was applied even after heating at 100 °C for several hours.     

Isomorphous mixing of mesogenic anions and uncharged analogues in organised poly(ehtylene oxide)-alkali salt complexes

The preparation and characterisation of novel ionic polymer liquid crystal complexes of poly(ethylene oxide)–Na⁺ with mesogenic anions and their uncharged structural analogues in homogeneous mixtures are described. The systems discused most fully are the anion of the phenolic mesogen 4-n-hexyloxybenzylidene-4-hydroxy aniline (1 ) with its uncharged analogue 4-n-hexyloxybenzylidene aniline (1a ) and the anion of 5-(4-n-octyloxy-2,3-dicyanophenyleneoxycarbonyl)benzimidazo-le (2 ) and its uncharged analogue 4-octyloxy-2,3-dicyanophenyloxybenzoyl (2 ). Differential scanning calorimetry, wide angle x-ray diffraction and polarised light microscopy show that PEO–Na1 /1a and PEO–Na2 /2a are homogeneous mesogenic phases when Na1 or Na2 are present at 50% or less of the stoichiometric composition in complexes (EO : salt = 3 : 1) and the shortfall is made up from 1a or 2a uncharged analogues of 1a and related systems substituted by methoxy rather than hydrogen do not form homogeneous mixtures.     

含有两种介晶基元的侧链聚硅氧烷类液晶的热性能

将两种液晶体4－联苯二酚基－4′－（2－乙基已酰基）－4－烯丙氧基苯甲酸酯（M1）和4－烯丙氧基苯甲酰氧基－4′－甲氧基苯（M2）接枝到聚硅氧烷链上,用IRS、DSC、TGA、POM、SAXS和WAXD等对所得样品进行了测定。结果表明,含有两种介晶基元的聚硅氧烷类液晶,具有较宽的中介区间（240－255℃）,比只含有一种介晶基元的聚硅氧烷类液晶中介相拓宽约170℃左右,且低于室温具有液晶相（－18－8．7℃）,热分解温度在300℃以上,属于近晶结构。     

Nematic Anisotropic Liquid‐Crystal Gels—Self‐Assembled Nanocomposites with High Electromechanical Response

The uniqueness of liquid crystals (LCs) lies in the large anisotropies of their properties, which can be utilized to generate high electromechanical responses. In a properly oriented LC polymer system, an external electric field can induce reorientation of the mesogenic units possessing a dielectric anisotropy, which, when coupled with the shape anisotropy of the mesogenic units, can in turn produce large mechanical strain. Anisotropic LC gels, which can be obtained by in‐situ photopolymerization of the reactive LC molecules in the presence of non‐reactive LC molecules in an oriented state, are an example of such liquid‐crystal polymer systems. It is shown here that a homeotropically aligned LC gel in its nematic phase exhibits high electrically induced strain (> 2 %) with an elastic modulus of 100 MPa and a high electromechanical conversion efficiency (75 %) under an electric field of 25 MV/m. These anisotropic LC polymeric materials could provide a technologically compatible system for such applications as artificial muscles and as microelectromechanical devices.     

Thermally Recordable Cholesteric Liquid Crystalline Copolymers Containing Pendant Menthyl and Cholesteryl Groups

In order to investigate the effect of spacer length and linkages between the rigid mesogenic core and the terminal group on the molecular interaction and physical properties of polymers, a series of novel side chain liquid crystalline polymers were synthesized. These were composed of liquid crystalline monomers with six or eleven methylene segments as spacers, and chiral monomers end capped with menthyl or cholesteryl groups. Liquid crystalline phases of the polymers were investigated using differential scanning calorimetry and polarized optical microscopy, and confirmed with X-ray diffractometry. Color image recording of the synthesized polymer films was achieved using a thermal treatment, and then fixed by quenching. This investigation demonstrates that the introduction of carbonate linking groups between the rigid mesogenic core and terminal group decreases both the lateral molecular interaction and thermal stability of the liquid crystalline polymers. The RGB reflection colors of the cholesteric composite film could be tuned by varying the film temperature and applying an external field. The results of this investigation present significant scientific and practical contributions with respect to the development of unique cholesteric polymer materials.