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。     

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     

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。     

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。     

胆甾相液晶的合成

本文使用了二氯亚砜先制成酰氯,然后再与胆甾醇化合合成胆甾酯的方法制得胆甾相液晶。并使用了红外(IR)和热重／差热分析仪(TGA／SDTA)对所制得的胆甾酯进行了分析。     

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。     

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.     

Alignment behaviour of liquid crystals on ethyl cellulose films with banded‐texture structure

Films were formed by casting and shearing ethyl cellulose in chloroform at high coating speed and thin coating thickness. The films were used as alignment layers for liquid crystals. Atomic force microscopy and polarizing optical microscopy (POM) were used to identify the banded‐texture structure of the films. The alignments of nematic liquid crystal 4‐cyano‐4′‐n‐pentylbiphenyl (5CB) droplets on the films were observed by POM. Furthermore, the time‐dependent alignment behaviour of 5CB on the films was recorded and studied. © 2003 Society of Chemical Industry     

Synthesis of amphiphilic ethyl cellulose grafting poly(acrylic acid) copolymers and their self-assembly morphologies in water

Amphiphilic ethyl cellulose (EC)-g-poly(acrylic acid) (PAA) copolymers were synthesized by atom transfer radical polymerization (ATRP). Firstly, ethyl cellulose macro-initiators with the degree of the 2-bromoisobutyryl substitution of 0.04 and 0.25 synthesized by the esterification of the hydroxyl groups remained in EC macromolecular chains and the 2-bromoisobutyryl bromides. Secondly, tert-butyl acrylate was polymerized by ATRP with the ethyl cellulose macro-initiator and EC-g-PtBA copolymers were prepared. Finally, the EC-g-PAA copolymers were prepared by hydrolyzing tert-butyl group of the EC-g-PtBA copolymers. The grafting copolymers were characterized by means of GPC, ¹H NMR and FTIR spectroscopies. The molecular weight of graft copolymers increased during the polymerization and the polydispersity was low. A kinetic study showed that the polymerization was first-order. Meanwhile, EC-g-PAA copolymers were self-assembled to micelles or particles with diameters of 5 nm and 100 nm in water (pH = 10) when the concentration was 1.0 mg/ml.     

Holographic polymer dispersed liquid crystals (HPDLCs) containing triallyl isocyanurate monomer

The morphology and corresponding performance of holographic polymer dispersed liquid crystals (HPDLCs) based on thiol-ene polymer are dependent on a number of factors including the gel point conversion of the polymer, polymerization kinetics, and extent of liquid crystal (LC) phase separation. Previous research of HPDLC reflection gratings made from thiol-allyl ether polymer indicates that increasing polymerization rate in systems with moderate gel point conversion can improve diffraction efficiency (DE). This work examines HPDLC reflection gratings that contain the ene monomer triallyl isocyanurate (TATATO). In HPDLCs, thiol-TATATO polymerization is two times faster than the thiol-ene polymerization of triallyl ether. By substituting TATATO for triallyl ether, the LC droplet size within HPDLC reflection gratings decreases from 100 nm to 25 nm. The dramatic reduction in LC droplet size for thiol-TATATO HPDLCs increases baseline transmission from 55% in thiol-triallyl ether HPDLCs to 90% at 450 nm. Unfortunately, the DE of thiol-TATATO HPDLCs is only approximately 10% due to poorly defined lamellae in the grating morphology. As determined with real-time IR (RTIR) spectroscopy, thiol-TATATO HPDLCs have significantly faster LC demixing kinetics in comparison to thiol-allyl ether HPDLCs. During holographic photopolymerization, the increased rate of LC demixing causes formation of LC droplets throughout the grating. The low DE of thiol-TATATO HPDLCs can be improved by mixing TATATO and allyl ether monomer. The morphology of ternary thiol-ene HPDLC formulations containing TATATO and allyl ether has a well-defined grating structure due to increased LC solubility in the system, an average LC droplet size of 50 nm, and baseline transmission of nearly 85% at 450 nm.     

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     

醋酸丁酸纤维素与聚丙烯酸乙酯共混体系的研究

通过差热分析和拉伸试验研究了醋酸丁酸纤维素CAB－35－1与聚丙烯酸乙酯（PEA）物理共混、半一互穿网络共混体系的相容性和力学性能，并用扫描电镜观察了共混物的形态。     

Synthesis and characterization of novel monomers and polymers containing chiral (−)-menthyl groups

To investigate the steric effects of chiral menthyl groups on the induction of cholesteric liquid crystals and the sensitivity of the photoisomerizable azobenzene derivatives, a series of chiral monomers and a photoisomerizable chiral azobenzene derivative with various spacers end-capped with (−)-menthyl group were synthesized. The structures of the novel chiral compounds synthesized in this investigation were identified using ¹³C NMR, FTIR, and elemental analysis. The phase transition temperatures of the chiral compounds were investigated using X-ray diffraction, differential scanning calorimetry, and polarizing optical microscopy. The thermogravimetric characteristics, the glass-transition temperatures (T_g) and the weight-average molecular weights (M_w) of the homopolymers were also evaluated. Polymers containing chiral menthyl groups with a biphenyl segment were found to reveal high thermal resistance. However, the existence of the steric hindered menthyl group disturbed the arrangement of chiral monomers leading to the disappearance of liquid crystal phases. The specific optical rotation of the synthesized monomers and polymers were also evaluated. The effect of the synthesized chiral compounds, monomers and photoisomerizable azobenzene derivative on the induction of the cholesteric liquid crystal films was investigated. The morphological network structure of the polymer matrix inside a liquid crystal cell was studied using a scanning electron microscope (SEM). The phototuning ability of the AzoM on the cholesteric liquid crystals was also established.     

Aliphatic acid esters of (2-hydroxypropyl) cellulose—Effect of side chain length on properties of cholesteric liquid crystals

A series of aliphatic acid esters of (2-hydroxypropyl) cellulose (C_nPC) were synthesized via the esterification of aliphatic acid chloride and (2-hydroxypropyl) cellulose (HPC). The liquid crystalline (LC) phases and transitions were investigated using differential scanning calorimetry, wide-angle X-ray diffraction (WAXD), and polarized light microscope (PLM) techniques. This series of C_nPC polymers exhibited characteristic features of cholesteric LC phases between their glass transition and isotropization temperatures. The cholesteric LC characteristics were studied utilizing an ultraviolet/visible/near infrared spectrometer in a reflection mode. It was confirmed that, with an increase in the number of methylene units in the side chains of this series of C_nPC polymers, there was an increase, on the scale of nanometers, in the layer spacing values for the cholesteric LC phases measured by WAXD. This periodic layer spacing represents the thickness of the neighboring twisted layers in a helical structure. Based on a unique significant red shift of the maximum reflection peak for the LC phases in this series of C_nPCs, it is evident that the pitch distance in the helical structure also increases with an increase in the length of methylene units in the side chains.     

Ceric(IV) ion‐induced graft copolymerization of acrylamide and ethyl acrylate onto cellulose

Graft copolymerization of acrylamide (AAm) and ethyl acrylate (EA) onto cellulose has been carried out from their binary mixtures using ceric ammonium nitrate (CAN) as an initiator in the presence of nitric acid at 25 ± 1 °C. The extent of acrylamide grafting increased in the presence of the EA comonomer. The composition of the grafted chains (F_AAm = 0.52) was found to be constant during the feed molarity variation from 7.5 × 10^?2 to 60.0 × 10^?2 mol L^?1, whereas the composition of the grafted chains (F_AAm) was found to be dependent on feed composition (f_AAm) and reaction temperature. The effects of ceric(IV ) ion concentration, reaction time and temperature on the grafting parameters have been studied. The grafting parameters showed an increasing trend up to 6.0 × 10^?3 mol L^?1 concentration of CAN at a feed molarity of 30.0 × 10^?2 mol L^?1 and showed a decreasing trend on further increasing the concentration of CAN (>6.0 × 10^?3 mol L^?1) at a constant concentration of nitric acid (5.0 × 10^?2 mol L^?1). The composition of the grafted chains (F_AAm) was determined by IR spectroscopy and nitrogen content and the data obtained then used to determine the reactivity ratios of the acrylamide (r₁) and ethyl acrylate (r₂) comonomers by using a Mayo and Lewis plot. The reactivity ratios of acrylamide and ethyl acrylate were found to be r₁ = 0.54 and r₂ = 1.10, respectively, and hence the sequence lengths of acrylamide (m?M₁) and ethyl acrylate (m?M₂) in the grafted chains are arranged in an alternating form, as the product of the reactivity ratios of acrylamide and ethyl acrylate (r₁ × r₂) is less than unity. The rate of graft copolymerization of the comonomers onto cellulose was found to be dependant on the ‘squares’ of the concentrations of the comonomers and on the ‘square root’ of the concentration of ceric ammonium nitrate. The energy of activation (ΔE_a) of graft copolymerzation was found to be 5.57 kJ mol^?1 within the temperature range from 15 to 50 °C. On the basis of the results, suitable reaction steps have been proposed for the graft copolymerzation of acrylamide and ethyl acrylate comonomers from their mixtures. Copyright © 2005 Society of Chemical Industry