溶剂的溶胀与乙基氰乙基纤维素胆甾相结构变化

乙基氰乙基纤维素 [(E -CE)C]/聚丙烯酸 [PAA]分子复合物通过用光引发聚合乙基氰乙基纤维素 /丙烯酸胆甾型液晶溶液中的丙烯酸得到。在 (E -CE)C/PAA分子复合物中 ,PAA在水中的溶胀影响到胆甾型液晶相结构。胆甾型液晶相选择性反射光的波长随着PAA的溶胀向长波方向位移。同时还发现 ,在PAA溶胀过程中胆甾型液晶相的螺距增加 ,取向分子层之间的距离减小。     

光聚合对乙基氰乙基纤维素/丙烯酸胆甾相结构的影响

乙基氰乙基纤维素 [(E -CE)C]能够很好地溶解在丙烯酸 (AA)中并形成胆甾型液晶溶液。在 (E -CE)C/AA溶液中加入适当的光引发剂 ,采用紫外光引发聚合抑制聚合过程中相分离的发生 ,可以制得保持胆甾相结构的复合物。聚合反应会对胆甾相的结构产生一定的影响。文章研究了溶液浓度、聚合温度和 (E -CE)C分子量等因素对聚合以后胆甾相选择反射光波长及结构的影响。     

分子结构对乙基氰乙基纤维素/丙烯酸胆甾型液晶性的影响

乙基氰乙基纤维素 [(E -CE)C]可溶于丙烯酸 (AA)形成胆甾型溶致液晶体系 ,液晶溶液的临界浓度 (C1 )与 (E -CE)C的分子量 (MW)有关 ,MW 越高 ,C1 越低。同时 ,C1 还受 (E -CE)C氰乙基取代度 (DS)的影响 ,DS越大 ,C1 越低。相同DS时 ,胆甾相的螺距 (P)随MW 增加而增大 ;在MW 相近时 ,随DS的升高 ,P先减小 ,后增大 ,在DS 0 .2～ 0 .3之间有最小值。P随 (E -CE)C/AA溶液浓度的增大而降低。 (E -CE)C/AA溶液中的AA快速聚合后 ,体系胆甾相选择性反射光的能力和选择性均有所降低 ,并且最大选择性反射光的波长 (λmax)蓝移。聚合前溶液的浓度越小 ,聚合后λmax的变化值越小     

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     

磁场对乙基氰乙基纤维素胆甾型液晶相的影响

乙基氰乙基纤维素 [(E -CE)C]形成的胆甾型液晶相结构和形貌会因溶液浓度和溶剂的不同而变化。通过偏光显微镜 ,X -ray衍射和透射电子显微镜研究 ,讨论了强磁场 ( 9.4T)对不同浓度和溶剂的 (E -CE)C胆甾相液晶溶液结构的影响。     

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     

乙基氰乙基纤维素溶致液晶的缺陷结构观察

乙基氰乙基纤维素在许多溶剂中都可以形成胆甾型液晶溶液。在液晶溶液中出现多种向错结构。本文利用偏光显微镜和电子显徽镜对液晶溶液中出现的向错结构进行了全面的观察。观察到了λ,τ和x向错线以及各种由具有相反符号的λ和τ向错线组成的向错对,其结构特征与小分子胆甾型液晶相结构特征相似。     

酸解时间对纳米晶纤维素胆甾相液晶的影响

研究了酸解时间对纳米晶纤维素薄膜颜色和螺距的影响。以棉短绒为原料,采用硫酸酸解法,以酸解时间为影响因素,制备了三种纳米晶纤维素(CNC)悬浮液,再将三种悬浮液放入烘箱干燥,制成具有不同颜色的纳米晶纤维素薄膜。采用Zeta电位及纳米粒度分析仪对CNC悬浮液的Zeta电位和粒径进行表征。采用紫外可见近红外分光光度计(UV-vis-NIR)、全反射傅里叶红外光谱仪(FT-IR)、X-射线衍射仪(XRD)、扫描电子显微镜(SEM)以及偏光显微镜(POM)对薄膜进行表征进而研究了酸解时间对纳米晶纤维素胆甾相液晶螺距的影响。结果表明,随着酸解时间增长,CNC的粒径减小,引入的磺酸酯增多,表面负电荷增大,颗粒之间静电斥力增大,最终导致螺距增大,薄膜的反射波长红移,薄膜的颜色从蓝色逐渐转向红色。     

壳聚糖的制备及其液晶表征

天然高分子材料壳聚糖因其具有抗菌性且具有类似纤维素的性质:可再生、良好的生物相容性、分子具有双螺旋结构、分子结构具有刚性等,且壳聚糖分子还具有良好的抗菌性,其在纺织领域被人们广泛关注。但壳聚糖纤维存在强度不高的缺点,而液晶化合物具有高强度的优点,故对其液晶性的研究日益增多。本文利用浓碱法自制的虾壳壳聚糖在乙酸中液晶临界质量分数仅为1%,并通过偏光显微镜观察到其在酒石酸、丙酸和对甲苯磺酸溶液中显示出典型的胆甾型液晶所具有的指纹状织构,即具有溶致液晶性。壳聚糖在羧酸溶液中随着羧酸的碳链增长,其液晶织构的螺距值亦逐步增大:在甲酸中为13.8~15.5μm,在乙酸中为15.5~17.2μm,在丙酸中增至19.8~22.4μm。     

胆甾液晶弹性体的合成及液晶性能研究

以胆甾液晶单体和向列液晶交联剂与含氢聚硅氧烷接枝聚合制备了一系列弹性体.通过红外光谱(FT-IR)、核磁氢谱(1 H-NMR)确定了液晶单体及弹性体的化学结构.通过差热扫描量热仪(DSC)、偏光显微镜(POM)以及X-射线衍射研究了其介晶性质及液晶相行为.结果表明,弹性体的玻璃化转变温度随着向列液晶交联剂的加入先降低后升高.随着向列液晶交联剂的加入,系列弹性体的X-射线衍射峰弥散,且最大反射波长略微变长,说明液晶分子间的有序性受到干扰.     

Influence of polymerization on the cholesteric structure in ethyl-cyanoethyl cellulose/acrylic acid solutions

Ethyl-cyanoethyl cellulose ((E-CE)C) forms cholesteric liquid crystals in acrylic acid (AA) and the cholesteric order in the solutions can be frozen when the AA is quickly polymerized but the cholesteric structure is changed after the polymerization though the property of the selective reflection is reserved. The maximum wavelength of the selective reflection of the cholesteric phase λ_max is shifted to the shorter wavelength direction and the selectivity and the intensity of the reflection are decreased after the AA polymerization. It is found that the shift of the reflection wavelength results from the decrease of the cholesteric pitch after the polymerization and the variation of the cholesteric pitch is decreased with increasing the (E-CE)C concentration. The decrease of the pitch after the AA polymerization is due to the volume shrinkage of the solvent monomer during the polymerization and it depends on the polymerization temperature.     

Effect of swelling on the cholesteric structure of ethyl‐cyanoethyl cellulose/crosslinked poly(acrylic acid) composite films

The swelling behavior of ethyl‐cyanoethyl cellulose [(E‐CE)C]/crosslinked poly(acrylic acid) [PAA] cholesteric liquid crystalline composite films and the structural variation of the cholesteric phase during the swelling and the drying process were studied. It was found that the wavelength of the selective reflection of the composite films was shifted to the long wavelength direction during swelling. Both the pitch of the cholesteric phase and the distance between neighboring molecular layers were increased, and the helix axis was inclined after swelling. Moreover, the swelling behavior of the composite films in water was reversible, which means that the optical properties and structural characters of the films could be changed back to their original states after the films were dried from the equilibrium swelling state. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3574–3578, 2004     

Optical properties of (acetoxypropyl)cellulose mesophases: factors influencing the cholesteric pitch

(Acetoxypropyl)cellulose (APC) forms a thermotropic cholesteric liquid crystalline phase, and with dibutyl phthalate (DBP) it also forms a lyotropic cholesteric phase. The reflection bands for the mesophases occur in the visible region, at wavelengths which depend on concentration and temperatures. The pitch of the cholesteric helicoidal structure is derived from measurements of the mean refractive indices and of the reflection band wavelengths for mesophase samples containing from 0 to 30% diluent at temperatures from ambient to 170°C. The pitch of the thermotropic mesophase increases with increasing temperature and with decreasing molar mass. The pitch of the lyotropic mesophase increases with increasing temperature and diluent content. Pitch values approach infinity at temperatures close to the clearing temperature of the mesophase, and no reversal in the sense of the pitch with temperature or diluent content was detected. The experimentally observed changes in pitch with composition and temperature are in reasonable agreement with the predictions of a recent theory for cholesteric mesophases composed of helical rod-like species. The average distance between chains in the mesophase is estimated from X-ray diffraction measurements, and hence the average angle of twist between neighbouring APC molecules may be found. The angle decreased from 2.2° for pure APC to 0.9° for a volume fraction of 0.73 APC in DBP.     

Optical properties of ethyl‐cyanoethyl cellulose/poly(acrylic acid) cholesteric liquid crystalline composite films

Ethyl‐cyanoethyl cellulose [(E–CE)C]/poly(acrylic acid) (PAA) composite films were prepared by photopolymerizing acrylic acid (AA) in (E–CE)C/AA cholesteric liquid crystalline solutions. With the selection of suitable concentrations, (E–CE)C/PAA composite films showed vivid colors due to the selective reflection property of the cholesteric phase. It was found that the wavelength of reflection was a function of the concentration of (E‐CE)C, and the reflectivity was increased with increasing thickness of the film. The selective reflection of the composite holds well upon heating at temperatures below 160°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 213–217, 2004     

Mechano-Optical Response of Novel Polymer Composites Based on Elastic Polyurethane Matrix Filled with Low-Molar-Mass Cholesteric Droplets

Among the various types of liquid crystalline (LC) structures, the cholesteric mesophase attracts special attention in view of helical supramolecular structure determining their specific optical properties. The helix pitch of cholesteric liquid crystals is very sensitive to mechanical stress, resulting in change of their optical properties and position of selective light reflection peak. Here, films of polymer-dispersed cholesteric liquid crystals based on polyurethane elastomer are prepared and studied. Liquid crystal mixtures based on chiral cholesterol derivatives are uniformly dispersed in the form of micrometer-sized droplets in an elastomeric matrix. A significant mechano-optical response of the composites under the action of deformation is demonstrated, and the change in the position of the selective light reflection band during mechanical stress is studied in detail. A shift in the selective light reflection peak by 100 nm or more is found. This process is accompanied by color transformations of brightly colored films. Such materials can be promising for creating stress and deformation sensors, ripple and bending sensors, and other technical devices.     

Thermotropic cholesteric mesophases in copoly(γ-n-alkyl l-glutamate)s

Summary Thermotropic cholesteric mesophases were found for three types of -helical copoly(-n-alkyl L-glutamate)s; the combination of the n-alkyl groups was methyl-hexyl, methyl-octyl, and propyl-octyl. Cholesteric colors due to the selective reflection were observed in the temperature range from 110 to 190°C for the films with copolymer compositions of about 50/50 in mol%. These thermotropically mesomorphic copolymers had disordered structures in the molecular packing as inferred from the x-ray diffraction patterns. The cholesteric sense was right-handed, since the negative circular dichroism associated with the cholesteric pitch was observed for all the mesomorphic films. The temperature dependence of the pitch was discussed in comparison with that of lyotropic liquid crystals of these polymers.