纤维素衍生物/二氯乙酸液晶溶液的织态结构[摘]

纤维素衍生物,如乙基纤维素,甲基纤维素,乙基氰乙基纤维素,乙基醋酸纤维素等与二氯乙酸所形成的溶液在浓度达到临界值以上后,出现胆甾型液晶相。在这类溶液中,液晶相的织态结构具有多重性,即胆甾型液晶相的织构随溶液浓度和温度而变化。在不同的浓度范围内,溶致性液晶可呈现出圆盘织构,条纹织构,假各向同性织构和具有鲜艳色彩的平面织构。这些织构均具有胆甾型液晶的特征。在液晶相刚形成,溶液处于     

纤维素液晶研究领域取得重要进展

纤维素是一种生长和存在于绿色植物中的丰富的可再生的(年再生850亿吨)天然高分子材料,纤维素材料的开发利用在高分子科学的建立、发展和工业应用方面都起到了重要的作用。特别是在石油资源开始逐步枯竭的时期,纤维素资源有可能代替石油成为现代化学工业的基本原料之一。中国科学院广州化学研究所纤维素化学重点实验室黄勇研究员和王林格博士领导的研究小组长期以纤维素衍生物所形成的液晶相为主要对象开展基础和应用方面的研究。最近在国家杰出青年基金项目的支持下,该研究小组利用可聚合单体作为溶剂对纤维素衍生物胆甾型液晶相溶液中各织…     

纤维素及其衍生物液晶

从纤维素及其衍生物的化学结构出发,综合论述了纤维素衍生物的合成方法,液晶态的形成理论,液晶性能及其在塑料中的应用。     

液晶双马来酰亚胺/环氧树脂共聚物的制备

本文采用含柔性链（C10）的液晶双马来酰亚胺和含联苯基的液晶环氧树脂合成共聚物，经FTIR、DSC、偏光显微镜、SEM表征了该共聚物的结构与液晶特征。结果表明该共聚物具有较好热致液晶性，其液晶织态呈向列型织构，亦能保留在交联网络结构中。     

浓度和边界条件对纤维素胆甾相聚集态结构的影响

对不同边界取向条件和不同浓度下乙基氰乙基纤维素 /二氯乙酸溶液形成的胆甾型液晶相的聚集态结构及其光学性能进行了研究和讨论。在胆甾相与各向同性相共存时 ,随着浓度的变化 ,溶液会呈现出多种织构形态。在边界垂直取向条件下 ,液晶分子趋向于焦锥排列 ,在边界平行取向条件下 ,液晶分子趋向于平面排列。另外 ,两相界面表面张力能抑制边界取向作用力对胆甾相聚集态结构的影响     

纤维素及其衍生物的液晶态与应用

本文讨论了纤维素及其衍生物的液晶态与应用。     

细菌纤维素苯甲酸酯的合成与表征

以细菌纤维素（BC）为原料,通过酯化反应制备细菌纤维素苯甲酸酯（BBC）,探讨了硝基苯用量、反应时间、反应温度以及苯甲酰氯用量对细菌纤维素苯甲酸酯取代度的影响。分别用红外光谱（FTIR）、差示扫描量热法（DSC）、偏光显微镜（POM）和广角X-射线衍射（WAXD）对产物结构、热致液晶织构和性能进行了表征。结果表明,细菌纤维素苯甲酸酯在281．7～356．3℃之间可以形成近晶型液晶相,其熔点和清亮点比已报道的植物纤维素苯甲酸酯的更高。     

基于氮杂氟硼二吡咯染料的柱相液晶

近年来Aza-BODIPY染料因其优异的光学性质备受关注。利用"click"反应合成了包含三氮唑及3，4，5-三（十二烷基）苯甲酰胺单元的Aza-BODIPY染料1，并通过¹H NMR、¹³C NMR和MS等方法表征了其化学结构。Aza-BODIPY染料1在偏光显微镜下呈现典型的扇形织构。差示扫描量热法（DSC）研究中观察到了此材料的固相-液晶相以及液晶相-液相的相转变。进一步利用小角X射线衍射（SAXD）研究了液晶相的结构，结果表明Aza-BODIPY染料1形成了六方柱状液晶相（Col_hd）。据我们所知，这是首例基于Aza-BODIPY染料的柱相液晶材料。     

由液晶制备高性能纤维素纤维

液晶纺丝是一类纺制高性能纤维的重要方法，由纤维素及其衍生物液晶纺制高性能纤维具有突出的原料优势。本文主要综述了液晶纤维素及其衍生物纤维的制备、结构及力学性能等方面的国内外进展情况，以利于对高性能纤维素纤维产品的研究和开发应用。     

热致液晶性羟乙基纤维素醋酸酯等温相转变动力学

利用DSC研究了热致液晶性羟乙基纤维素醋酸酯（HECA）等温相转变动力学。发现在等温条件下，HECA形成液晶相的过程可以用描述结晶过程的Avrami方程来描述。所得到的Avrami指数n约等于2，这表明在无热成核以后，液晶相以二维的方式生长。HECA液晶相形成的相转变比高聚物的结晶过程快许多，其相转变热也很低。液晶相转变的速率在所研究的温度范围内先随着相转变温度的升高而增大，到一极大值以后又逐渐降低。对于本文所研究的HECA样品，液晶相的形成在421K时最快。     

Textures of ethyl cellulose–dichloroacetic acid mesomorphic solution

Textures of the ethyl cellulose (EC)-dichloroacetic acid (DCA) mesomorphic solution were studied systematically by polarizing microscopy and small-angle light scattering. It was found that with increasing polymer concentration, the mesophase could show a disklike texture, an oil streak texture, a pseudoisotropic texture, and an iridescent planar texture. Within the mesophase the ordering degree is different in different zones. The phase transition between anisotropic and isotropic phases could also be accomplished by changing temperature. With increasing temperature the mesophase with the lower degree of order could first transform to the isotropic phase and the phase transition from an anisotropic phase with a higher degree of order to the isotropic one could take place only at the higher temperature. A disklike texture was also observed during the phase transition between the anisotropic and isotropic phases when the solution was heated and it was probably a basic texture in polymer cholesteric liquid crystals.     

Synthesis and mesomorphic behavior of terminally carboxyl oligo(ethylene oxide) monomethyl ethers-substituted side chain liquid crystalline polysiloxanes. I

A series of alkene monomers containing carboxyl biphenyl benzoate ester or carboxyl p,p′-phenyl benzoate ester based on mesogenic core with a carboxyl (±)-2-methyl ethylene glycol monomethyl ether group or various lengths of carboxyl oligo (ethylene oxide) monomethyl ethers as the terminal group were synthesized. And they were grafted onto the poly(methylhydrosiloxanes) (PMHS) by the platinum catalyzed hydrosilylation process. Their molecular structure, the thermal transitions temperature, and mesophase texture of monomers and of polymers were characterized using ¹H nuclear magnetic resonance, differential scanning calorimetry, and polarizing optical microscopy with hot stage. The polymers obtained all show smectic phase while their precursor monomers show both smectic and/or nematic phase, or in some cases, no mesophase. The factors governing mesophase texture and transition temperature are discussed. © 1993 John Wiley & Sons, Inc.     

Synthesis,characterization, and mesomorphic behavior of side-chain liquid crystalline copolysiloxane polymers I. with an oligo (ethylene oxide) unit and a cyano unit in the side chain

The syntheses and characterizations of poly [4-allyloxy-benzoic acid [4-(2-methoxy) ethoxy] biphenyl]-4-yl ester-co-4-allyloxy-[(4-cyano)-4-phenyl] carboxyl benzoate ester (poly [(MS3BDBE1)-co-(MCN)]_x/y) (where x/y represents the molar ratio of the two structural units on the side chain) were performed in this study. The molar compositions of the structural units on the copolymers side chain were characterized by¹H NMR. The transition temperatures, mesophase texture, and layer spacing (dl) of the polysiloxane polymers and copolymers were determined by differential scanning calorimetry (DSC), polarized optical microscopy, and X-ray diffraction patterns. The effects of the molar composition in the copolymers on the mesophase texture, transition temperatures, enthalpy/entropy change of mesophase/isotropic transition, dl of these copolymers were also discussed.     

Thermotropic liquid crystalline behaviors of ethylcellulose

The thermotropic liquid crystalline behaviors of ethylcellullose (EC) were investigated by DSC, polarizing microscope with hot stage, and capillary rheometer. It was found that only those EC that have the ethoxyl content over 45% can exhibit the thermotropic liquid crystalline behaviors: the DSC trace showed the transition from mesophase to isotropic phase, the texture appeared under the crossed polarizer, and the rheological flow curves exhibited two yield points.     

Phase transformations in a thermotropic liquid crystalline copolyester and its blends with polyether sulfone

Mesophase transitions in a thermotropic liquid crystalline polymer comprising p-hydroxybenzoic acid (PHB) and polyethylene terephthalate (PET) in a copolymer ratio of 60/40 were studied by means of optical microscopy, light scattring, and wide-angle X-ray diffraction (WAXD). According to time-resolved light scattering and optical microscopic studies, at about 250°C, a mesophase transition was evident in which Schlieren texture developed with elapsed time. This transition has been identified as a solid crystal-nematic mesophase transition associated with the melting of PHB-rich crystals. It is concluded that the copolymer sequence may not be random. An isotropic, amorphous blend of PHB-PET/polyether sulfone (PES) was prepared by solvent casting from hexafluoro-2-propanol solution. However, this homogeneous blend appears to be kinetically entrapped during solvent removal. Thermally induced phase separation takes place upon heating slightly above the glass transition temperature of PES. Morphology development within phase-separated domains has been qualitatively examined by light scattering and optical microscopy.     

催化裂化油浆溶剂抽提及其中间相沥青

考察了FCC油浆及其在不同温度、不同剂油比条件下抽出油的组成和性质。确定了最佳抽提条件为50℃，剂油比为2：1。计算所得选择性表明糠醛是分离FCC油浆的有效溶剂。抽出油形成的中间相沥青，具有良好的可溶性，显现广域流线型大融并体，分子排列规整，具有较佳的流动性，是一种易石墨化炭。抽余油形成的中间相沥青，显示粗镶嵌结构，可溶性较差，难以制取上佳炭材料，但可回收作催化裂化原料。     

Synthesis and structure of polysiloxane liquid crystalline elastomers with a mesogenic crosslinking agent

A new mesogenic crosslinking agent M‐1 was synthesized to minimize the perturbations of a nonmesogenic crosslinking agent for liquid crystalline elastomers. The synthesis of new side‐chain liquid crystalline elastomers containing a rigid mesogenic crosslinking agent M‐1 and a nematic monomer M‐2 is described by a one‐step hydrosilylation reaction. The chemical structures of the obtained monomers and elastomers were confirmed by ¹H NMR and FTIR spectroscopy. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction measurements. The influence of the crosslinking units on the phase behavior is discussed. The elastomers containing less than 15 mol % of the crosslinking units showed elasticity, reversible phase transition, and nematic‐threaded texture. However, when the crosslinking density reached 21.6 mol %, the mesophase of polymer P‐8 disappears. The adoption of a mesogenic crosslinking agent diminishes the perturbation of a nonmesogenic crosslinking agent on mesophase of liquid crystalline elastomers, and isotropic temperature and a mesomorphic temperature range slightly decreased with increasing content of the crosslinking agent. In addition, X‐ray analysis shows nematic polydomain network polymers can transform into smectic monodomain by stress induction, leading to the orientation formation macroscopically. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1736–1742, 2004     

The role of liquid crystals in the formation of graphitizable carbons (cokes)

The formation of cokes and graphites proceeds via the creation from the isotropic fluid phase of carbonization of pitch and coal, of lamellar nematic liquid crystals or mesophase. This anisotropic fluid, deformable mesophase, develops as spheres within which constituent molecules are stacked parallel to an equatiorial plane. This type of structure facilitates coalescence to a coherent mass which eventually forms a graphitisable carbon. The ‘onion-skin’ structure of mesophase spheres cannot so coalesce. Different optical textures of cokes and graphites owe their origin to different chemical reactivities and fluidities of mesophase, the lower the fluidity the smaller the size of the optical texture. Mesophase from lameller molecules is compared with conventional rod-like nematic liquid crystals. Structures in needle-cokes, metallurgical coke, coke from solvent refiend coal and carbon fibre from pitch are discussed in terms of formation and properties of lamellar nematic liquid crystals.     

Structural study of cokes using optical microscopy and X-ray diffraction

Cokes exhibiting a range of optical texture from isotropie to anisotropic domains > 60 μm diameter were examined by X-ray diffraction. The variation of an optical texture index (OTI) with crystallite height and interlayer spacing was studied. The OTI varies little with the X-ray parameters for cokes whose optical texture is larger than medium-grained (1.5–5.0 μm) mosaic anisotropy. For cokes of smaller optical texture there is a sharp decrease in crystallite height and an increase in interlayer spacing. These results are discussed in terms of fluid mesophase removing defects in cokes of optical texture of size of coarsegrained mosaics and larger. The cokes of smaller optical texture are formed from less fluid mesophase which does not coalesce. Defects therefore remain in this anisotropic carbon of the coke so reducing crystallographic order.     

Effect of the different rigidity of the chiral crosslinker on phase behaviors of side‐chain chiral liquid crystalline elastomers

In the present work, the phase behaviors of two series of side‐chain liquid crystalline elastomers ( PI and PII series) derived from the same nematic liquid crystalline monomer and the different rigidity of chiral bisolefinic crosslinking units have been compared and studied extensively, and the effect of the different rigidity of crosslinker on the phase behavior of elastomers has been discussed. The chemical structure of the monomers and polymers obtained were confirmed by FTIR and ¹H NMR spectroscopy. The phase behaviors were investigated by differential scanning calorimetry, polarizing optical microscopy measurement, thermogravimetric analyses, and X‐ray diffraction measurement. The two series of elastomers showed smectic or cholesteric phases. When the amount of different crosslinking units was less than 15 mol %, both of the elastomers displayed elasticity, reversible phase transition with wide mesophase temperature ranges, and high thermal stability. It is shown that the isotropization temperature values of PII series are higher than those of PI series, and the glass transition temperature values of PII series varied smoothly and that of PI series changed smoothly first and then abruptly with increasing the contents of crosslinkers with different rigidity. In addition, PI series showed an interesting change in LC texture near clearing point, but PII series did not. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008