乙基醋酸纤维素溶致性液晶的研究

非全取代的乙基纤维素在浓硫酸催化下与醋酸反应,生成乙基醋酸纤维素。乙基醋酸纤维素在适当的条件下可以形成溶致性液晶。随浓度的升高,溶液从各向同性态经两相共存,转变成完全的液晶态。在加热溶液时,可以看到两相共存状态的形成和液晶相的完全消失,降低温度,液晶相又可以再生成。在液晶相生成的过程中,存在过冷现象,液晶聚集的区域由许多微小的取向区域组成,它们的取向方向不相同。溶液的n—c曲线在各相同性、两相共存和液晶态区域内是直线,但在这些相态之间相互转变时出现转折点。溶液的双折射△n=ne—no在两相共存与液晶态相互转变时也会发生较大变化。乙基醋酸纤维素大分子链的刚性随有机酸溶剂体系的酸的强度增大而增大,使临界浓度C_1~*随溶剂酸的强度的增大而减小。     

乙基醋酸纤维素溶致性液晶的研究

乙基醋酸纤维素溶于三氟乙酸、二氯乙酸、醋酸中.在浓度大于临界浓度时,形成胆甾型液晶态.溶液随浓度的增加,从各向同性态经两相共存转变成液晶态.在加热液晶溶液时,溶液转变成各向同性态.降低温度,液晶相再生成.在形成液晶过程中,存在过冷现象.在一定的条件下,液晶相以球状的形式存在.溶液的双折射△n在两相共存与完全液晶态间相互转变时会发生较大变化.乙基醋酸纤维素大分子链的刚性随有机酸溶剂体系的酸强度的增大而增大,使临界浓度C_1~*随溶剂酸强度的增大而减小.     

氰乙基纤维素液晶溶液光学性质的研究

氰乙基纤维素/二甲基甲酰胺溶液在高分子浓度达到一定值C_1~*时,可以形成液晶态。随浓度的增加,各向同性溶液经过一个两相共存区而转变成为完全各向异性的体系。通过观察溶液的双折射,测定溶液的折射率和消光度,确定出了溶液的临界浓度C_1~*和C_2~*。并用观察溶液双折射的方法测定了不同浓度下溶液的相转变温度Tc,得到了该溶液的T—C相图。讨论了在该体系中液晶态的形成过程。     

氰乙基纤维素溶致性液晶折射率的研究

本文用折射率法研究了氰乙基纤维素在二甲基甲酰胺和二甲基亚砜中形成溶致性液晶的过程,测定了临界浓度C_1~*和C_2~*。对用该方法研究高聚物液晶溶液的有效性以及折射率与其浓度和溶液结构的关系进行了探讨。讨论了各种情况下的n—C曲线。     

甲基纤维素/二氯乙酸液晶溶液的相转变

本文研究了甲基纤维素/二氯乙酸液晶溶液液晶相与各向同性相之间相互转变的过程。在连续升温过程中,由于液晶相内部有序度的非均一性,升温速率对液晶相织构随温度的变化有较大的影响。在等温相转变过程中,无论是从各向同性态转变为液晶态,还是其逆过程,从液晶态转变为各向同性态,相转变曲线均具有指数方程特征。利用与 Avrami 方程相似的指数方程进行处理,在从各向同性态转变为液晶态时,指数 n 大部分约为1。但液晶相向各向同性相在低于 Tc 时的相转变中,n 均小于1。相转变速率受溶液浓度和温度的影响。在质量分数为0.259的浓度时,液晶相向各向同性相的转变在低于 Tc 时39.5℃进行得最快。     

磺酸型双子表面活性剂的溶致液晶结构研究

合成了一种磺酸型双子表面活性剂6,6 -(丁基-1,4-二基双氧)双(3-壬基苯磺酸)(9BA-4-9BA), 利用偏光显微镜和X射线衍射分析仪研究了其在水溶液和乙酸乙酯溶液中的溶致液晶结构变化. 结果表明, 9BA-4-9BA在两种溶剂及其混合溶剂中均可出现溶致液晶态结构, 并且双子表面活性剂的溶致液晶相态与溶液浓度和溶剂种类密切相关. 随着浓度增加, 9BA-4-9BA水溶液溶致液晶结构由立方相经由片层立方相转变为层状液晶相, 乙酸乙酯溶液中主要以层状液晶相存在.     

氰乙基纤维素/二甲基乙酰胺液晶溶液的研究

本文利用 Abbe'折射仪和热台偏光显微镜研究了氰乙基纤维素/二甲基乙酰胺液晶溶液的形成、结构和某些性质。它与许多溶致性液晶一样,随溶液浓度的增加,溶液从各向同性状态经过两相共存状态转变成为单一的液晶态。溶液的双折射△n 随浓度增加而增加,随温度的升高而降低。升温速率的改变对测定临界温度值有一定的影响。液晶相在无外力作用时由许多取向的、无规分布的微区域组成。受到切应力后,微区变成长条状。分子链沿切应力方向取向,并在垂直于切应力方向上在各微区域内排列有序,相邻两微区的分子链的取向方向稍有不同。     

聚苯撑苯并二噻唑的甲基磺酸溶液的相转变过程及其动力学研究

用退偏振光强度法及偏光显微镜研究了溶致性液晶高分子聚苯撑苯并二噻唑的甲基磺酸溶液(PBT/MSA)由液晶相至各向同性相(N→I转变),及由各向同性相至液晶相(I→N转变)的相变过程.液晶相的形成(I→N)服从Av-rami方程,Avrami指数为1左右,表明该体系的液晶相是以一维棒状方式形成的.相转变温度与浓度有关,提高温度可加速在应力下液晶相长程有序结构的形成.     

聚苯撑苯并二噻唑的甲基磺酸溶液的相转变过程及其动力学研究

 用退偏振光强度法及偏光显微镜研究了溶致性液晶高分子聚苯撑苯并二噻唑的甲基磺酸溶液(PBT/MSA)由液晶相至各向同性相(N→I转变),及由各向同性相至液晶相(I→N转变)的相变过程.液晶相的形成(I→N)服从Av-rami方程,Avrami指数为1左右,表明该体系的液晶相是以一维棒状方式形成的.相转变温度与浓度有关,提高温度可加速在应力下液晶相长程有序结构的形成.     

乙基氰乙基纤维素/甲基丙烯酸酯液晶溶液的研究

乙基氰乙基纤维素/甲基丙烯酸酯在一定的浓度下可以形成溶致性液晶,从液晶相的双折射纹理结沟和小角光散射的Hν散射花样可知这类液晶是胆甾型的。同时,在液晶相开始出现时及各向同性相完全消失时的临界浓度C_1和C_2均随着甲基丙烯酸酯的酯基链增长而降低。     

半刚性乙酰氧丙基纤维素的制备与液晶相转变的影响研究

以羟丙基纤维素为原料,通过酯化反应合成了分子量较高的乙酰氧丙基纤维素,并用ＦＴ－ＩＲ表征了化学结构。以ＤＳＣ,Ｘ－ｒａｙ衍射ＰＬＭ和ＳＡＬＳ手段研究了产物的热致液晶相转变及其影响因素和溶致液晶性。实验表明,产物的乙酰基含量受合成温度和反应时间影响,其热致液晶的相转变温度和温域随乙酰基含量变化。     

甲壳素——一类新的液晶性多糖

"将甲壳素的结构与纤维素进行了比较, 并根据结构和链刚性指出其形成液晶态的可能性。简要介绍了制备液晶性甲壳素衍生物所必须的一些主要的化学修饰途径。叙述了15 种甲壳素衍生物的溶致液晶行为以及结构因素对它们液晶临界行为的影响。介绍了甲壳素衍生物形成的主要液晶态织构, 如指纹状织构、交替偏振场织构、条带织构和滴状织构, 以及甲壳素衍生物? 二氯乙酸溶液的热致相转变。综述了甲壳素的成纤性和液晶纺丝。     

聚己内酯分子量对乙基纤维素/聚己内酯共混体系的溶致性液晶织构的影响

利用偏光显微镜研究了乙基纤维素与聚己内酯共混物在二氯乙酸中的溶致性液晶形态。结果表明聚己内酯的分子量对共混体系的溶致性液晶结构有明显的影响。差示扫描量法测试显示含不同分子量聚己内酯的共混物,其混溶性及两组分间的相互作用无十分明显的差异。聚内酯分子量对共混体系溶致性液晶的形态和热稳定性的影响,可认为是由于分子量对体系的粘度贡献引起的。     

On the mechanism of photoinduced phase transitions in ternary liquid crystal systems near thermal equilibrium

According to their phase diagram, polyalkyl glycol ether dissolved in ternary solutions (water, alcane, and cyclohexane) lead to the formation of either liquid crystal phases or microemulsion phases. By photosensitization of the ternary system with laser dyes and choosing the adequate concentration and temperature conditions of these lyotropic systems, it is possible to photoinduce the phase transitions from the microemulsion phase to the liquid crystal phase (and vice versa). The phototransformation conditions were chosen in such a way that the system is in thermal equilibrium during the entire phase transition. The method of photo small angle x-ray scattering has been applied to investigate the mechanism of photoinduced phase transition. Spectroscopically, the mechanism of photoinduced phase transition has been characterized by optical absorption and emission techniques.     

Optical rotatory dispersion from liquid crystalline solutions and films of hydroxypropylcellulose

The chiroptical properties of (hydroxypropyl)cellulose (HPC) in methanol are measured by optical rotatory dispersion (ORD), both in isotropic solution and in the cholesteric liquid crystalline phase. The ORD spectra of HPC films cast from lyotropic solution are also examined. Isotropic solutions of HPC in methanol provide no ORD evidence for the presence of a helical conformation, or for concentration-induced changes in conformation. The ORD curve of HPC in methanol, when expressed as specific rotation, is independent of polymer concentration for isotropic solutions containing between 1 and 43 per cent polymer by weight. From the slope of Drude plots, the Cotton effect responsible for the observed ORD curve occurs at 175-180 nm. However a 45 per cent liquid crystal-line solution exhibits plain positive dispersion, and the magnitude of the specific rotation is also much greater than that found for solutions containing less than 43 per cent polymer. Results for more concentrated solutions confirm that ORD spectra of lyotropic liquid crystals of HPC in methanol contain a significant positive component that is not accounted for by the de Vries equation for cholesteric reflection. ORD measurements in other solvents and on dry films show that this contribution to the optical activity vanishes when the solvent is removed or when hydrogen bonding is disrupted. The effect is tentatively ascribed to a hydrogen bonded structure that contributes strongly to the optical rotation.     

Organic lyotropic lamellar liquid crystals

X-ray diffraction experiments on smectic A and C forming thermotropic liquid crystals reveal that the smectic layer spacing increases with the addition of organic solvents to the host material. The rate of this increase indicates the formation of an organic lyotropic lamellar liquid crystal phase in which the solvent is intercalated between the smectic layers of the host liquid crystal.     

The liquid-crystalline properties of selected cellulose derivatives

The liquid-crystalline properties of three cellulose esters, phenylacetoxy cellulose (PAC), 4-methoxyphenylacetoxy cellulose (4MPAC), and p-tolylacetoxy cellulose (TAC) and two cellulose silyl ethers, trimethyl silyl cellulose (TMSC) and t-butyldimethylsilyl cellulose (TBDMSC), are reported. Hot-stage polarized light microscopy provided evidence regarding the formation of thermotropic mesophases in the PAC, 4MPAC, TAC, and TMSC in bulk form upon heating. The concomitant DSC data showed further evidence of the thermotropic nature of these materials. PAC, 4MPAC, TAC, and TMSC formed lyotropic mesophases at 44, 48, 50, and 27 wt%, respectively in CH₂Cl₂. The presence of fingerprint patterns in wholly anisotropic solutions in conjunction with optical rotation measurements confirmed the cholesteric nature of these liquid crystalline solutions. TBDMSC formed neither a lyotropic nor a thermotropic liquid-crystalline phase due to the low degree of substitution (DS 0.68) of this derivative. The hydroxyl substituents of PAC, 4MPAC, TAC, and TMSC may be readily removed under mild conditions to regenerate cellulose.     

Concentration dependence of magnetic field effects on the ethyl-cyanoethyl cellulose/dichoroacetic acid cholesteric phase

The effects of an external magnetic field with intensity 9.4 T on the cholesteric phase in ethylcyanoethyl cellulose (E-CE)C]/dichloroacetic acid liquid crystalline solutions were investigated for different concentrations. It was found that the diamagnetic anisotropy of (E-CE)C is negative and the effect of the magnetic field on the orientation of the cholesteric phase is influenced by the concentration of the solution, because the liquid crystalline properties of the solutions vary with the concentration.