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     

Phase separation of the liquid crystal in the cholesterin phase

In the ethyl-cyanoethyl cellulose [(E-CE)C]/acrylic acid [AA]/4-cyano-4'-n-heptyl biphenyl (TCB) solutions, 7CB acted as a diluting reagent when it was added into the (E-CE)C/AA cholesteric liquid crystalline solutions. The dispersed phase with 250–300nm in size appeared after the AA in the isotropic (E-CE)C/AA/7CB solutions with the 7CB concentration (C_7CB) between 27.4 – 41.2wt% was polymerized at 24°C. There was the dispersed phase rich with 7CB in the (E-CE)C/AA/7CB cholesteric liquid crystalline solutions when C_7CB was 43.0wt% at 24°C. The temperature at which the anisotropic phase in the dispersed phase transformed to the isotropic phase in the solutions was increased after the polymerization of the AA, but the transition temperature of the dispersed phase in both the solutions and the films was lower than that of the pure 7CB. Received: 6 October 2000/Revised version: 18 December 2000/Accepted: 28 December 2000     

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.     

TEM observation of (E-CE)/PAA composite polymerized by ultraviolet initiation

From the ethyl-cyanoethyl cellulose (E-CE)C/acrylic acid (AA) solution, the (E-CE)C/PAA composite can be prepared by polymerizing the AA with ultraviolet initiation. The (E-CE)C/PAA composite prepared from the cholesteric liquid crystalline solution shows the lamellar structure with a periodicity ranging from 400 to 600 nm. In the lamellation there is no preferential orientation direction for polymer chains. The PAA is dispersed between the lamellea with small strip-like domains and the PAA and (E-CE)C have been homogeneously mixed in the system.     

Molecular structure and cholesteric liquid crystalline behavior of ethyl-cyanoethyl cellulose

Summary Ethyl-cyanoethyl cellulose [(E-CE)C] can form lyotropic cholesteric liquid crystals in acrylic acid (AA) and the liquid crystalline behavior is influenced by the concentration and (E-CE)C molecular structure. The critical concentration C₁ increases with increasing (E-CE)C molecular weight and is also influenced by the degree of substitution for cyanoethyl. The C₁ is lowest when the degree of substitution for cyanoethyl is 0.26. The pitch of cholesteric phase decreases with increasing both the (E-CE)C concentration and the degree of substitution for cyanoethyl and can not be influenced by the molecular weight of (E-CE)C in the molecular weight region of 6x10⁴–5x10⁵.     

Effects of cholesteric order on mechanical properties of (E-CE)C/PAA composites

The ethyl-cyanoethyl cellulose [(E-CE)C]/poly(acrylic acid) [PAA] composites were prepared via in situ photopolymerization of the (E-CE)C/acrylic acid (AA) solutions, in which the morphology and structure of (E-CE)C was retained as the same as that in the solution. The strength and the modulus of the composites depended on their morphology and structure. The strength of the composites with a completely amorphous state or with a completely cholesteric order did not significantly change with increasing (E-CE)C content, although the strength of the composites with completely cholesteric order is much higher than with the completely amorphous state. However, when the (E-CE)C content changed from 33.8% to 42.5%, in which the composites had both cholesteric order and amorphous phases, the strength of the composites greatly increased with increasing (E-CE)C. The elastic modulus of the composites with completely isotropic structure decreases with increasing (E-CE)C content but abruptly increases with increasing the fraction of cholesteric phase in the composites. The (E-CE)C with cholesteric order had a significant enhancing effect on the strength of the composites. The stress–strain curves indicated that the composites with completely amorphous or completely cholesteric order were breakable, while they were tough in the case when they had both cholesteric and amorphous phases. © 1995 John Wiley & Sons, Inc.     

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。     

Effects of concentration and boundary conditions on (E-CE)-C cholesteric phase

Effects of concentration and boundary conditions on the cholesteric liquid crystalline condensed state structure and optical property of ethyl-cyanoethyl cellulose were investigated. When cholesteric phase and isotropy phase were coexistent, the solution showed the multi-texture behavior with variation of concentration. With homeotropic anchoring boundary condition, molecules of cholesteric phase inclined to aggregate with focal-conics arrangement. With homogeneous anchoring boundary condition, molecules of cholesteric phase inclined to aggregate with planar arrangement. In addition, the effect of boundary anchoring on the cholesteric condensed state structure could be restrained by the surface tension of the interphase. Received: 13 March 2000/Revised version: 23 June 2000/Accepted: 28 June 2000     

Cellulose derivative‐based cholesteric networks

Ethyl‐cyanoethyl cellulose [(E‐CE)C]/acrylic acid (AA) solution could form cholesteric networks when the AA was quickly photopolymerized. The cholesteric structure in the solution was changed during the polymerization but the variation of the cholesteric order could be depressed by crosslinking of the system. The dependence of λ_max for the cholesteric phase on both the crosslinker concentration and the polymerization temperature was studied by UV‐Vis spectrometry. It was found that the cholesteric pitch variation is decreased with increasing the concentration of the crosslinking reagent and the water sensitivity of the cholesteric network is effectively suppressed and dependent on the types of crosslinker. The pitch of cholesteric network was decreased sharply with increasing the polymerization temperature, due to the increase of the volume shrinkage of the solvent during the polymerization. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1648–1653, 2005     

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。     

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     

Characterization and free radical polymerization of liquid crystalline acrylic acid/cellulose diacetate and N-vinyl-2-pyrrolidinone/cellulose diacetate solutions

Polymerizations of liquid crystalline solutions of cellulose diacetate (CDA) in acrylic acid (AA) and N-vinyl-2-pyrrolidinone (NVP) were conducted in an attempt to prepare molecular composites (polymer blends) processing a rigid rod polymer with liquid crystalline orientation. CDA was found to form liquid crystalline solutions in both AA and NVP at concentrations avove 40 wt% CDA. Polymerization of anisotropic 50 wt% CDA-AA and CDA-NVP solutions occurred with considerable retention of the starting solution anisotropy and yielded homogeneous blends (1 T_g) when the rate of polymerization was fast relative to the phase separation of the free radically polymerizing AA or NVP with CDA. Slow polymerizations lead to phase separated blends (2 T_g).     

Fine structure in cholesteric fingerprint texture observed by scanning electron microscopy

Summary The fine structure in some cholesteric fingerprint textures of cyanoethyl chitosan (CNCS)/acrylic acid solution and photo-solidified CNCS/polyacrylic acid composite film was studied using scanning electron microscopy (SEM), small angle light scattering (SALS) and polarizing optical microscopy (POM). Permanganic etching was developed to reveal the cholesteric liquid crystalline textures in the composite films. A schematic model was presented to explain this kind of fine structure. The directors within each cholesteric molecular layer did not orient in nematic-like order, but varied their orientation by an ill-defined period. Received: 4 October 1999/Revised version: 13 December 1999/Accepted: 24 December 1999     

Crosslinked hydroxypropyl cellulose films retaining cholesteric liquid crystalline order. I. Effects of cast conditions and heat treatment on the textures and order of films

To eliminate the shear-induced band texture and wrinkled texture observed on the free surface of cellulosic solid cast films retaining cholesteric liquid crystalline order, we proposed a storing process of the cast solutions: the solution is stored in the same solvent vapor atmosphere as the solution. The effect of cast conditions (the storing time) on those textures and the cholesteric liquid crystalline order was determined using the lyotropic liquid crystalline solution of hydroxypropyl cellulose in methanol with crosslinker. Furthermore, the effect of heat treatment on the liquid crystalline order in the cast films was determined. The resultant crosslinked films were observed with a polarized microscope and a scanning electron microscope, and were investigated with circular dichroism. Our findings showed that the proposed storing process is needed before starting the cast process. During the process the textures vanished, due to the relaxation of the residual stress in the solution, the cholesteric liquid crystalline order became stable, and the cholesteric pitch decreased with increasing storing time. The heat treatment also affected the liquid crystalline order of the films; the peak in the circular dichroism spectrum sharpened and shifted with heat treatment, and the shift in peak seemed to depend on the crosslinker concentration. Furthermore, the crosslinking proceeded with heat treatment. © 1995 John Wiley & Sons, Inc.     

Gel formation and liquid crystalline order in cellulose triacetate solutions

The formation of a liquid crystalline state of cellulose triacetate solution in trifluoroacetic acid was studied using optical microscopy, polarimetry and circular dichroism measurements. Below a critical concentration of $\text{34}\text{g}\text{100}\text{ml}$ a clear isotropic solution was formed. Solutions more concentrated than this were in the cholesteric liquid crystalline state. If water was added to the solution, a gel phase was formed if the polymer concentration was above a critical value. We interpret our observations in terms of the Pincus-de Gennes theory and show that the formation of liquid crystalline order involves both inter-and intramolecular forces.     

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     

Water‐soluble copolymers. III. Two‐step terpolymerization of acrylamide,acrylic acid,and acryloyloxyethyl trimethylammonium chloride

Terpolymerization of acrylamide (AM), acrylic acid (AA), and acryloyloxyethyl trimethylammonium chloride (DAC) was studied in aqueous solution by a two‐step polymerization method, consisting of adiabatic polymerization until reaching a maximum temperature and following retaining temperature for maturation. A redox agent:promotor triad‐initiating system was employed as an initiator. The effects of various parameters on terpolymerization were investigated. The optimum values were obtained at the DAC:AA molar feed ratio and the total monomer concentration, at the oxidant:reductant ratio and total redox agent concentration, and at the promotor concentration and redox agent:promoter ratio. The structure of the terpolymer was identified by Fourier transform infrared (FTIR) and ¹³C NMR spectroscopy. And the terpolymer composition was agreed favorably with feed ratio. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3278–3284, 2007     

Removal of methylene blue dyes from wastewater using cellulose‐based superadsorbent hydrogels

Superadsorbent cellulose‐graft‐acrylic acid (C‐g‐AA) hydrogels were successfully prepared via free radical polymerization in phosphoric acid solution. Phosphoric acid solution provides a homogeneous reaction system. The C‐g‐AA hydrogels have a porous network inner structure with cellulose as the backbone. The introduced carboxyl groups enable the C‐g‐AA hydrogels with good swelling property (swelling ratio 7327%) and excellent MB adsorption capacity (equilibrium adsorption amount 2197 mg g^?1). The dynamic swelling behaviors of the hydrogels were tested, water intake of hydrogels followed a non‐Fickian type diffusion. The effects of mole ratio of AA to cellulose, the pH of adsorption medium and the initial MB concentration on dye adsorption capacity of hydrogels were investigated. The adsorption isotherm and kinetics fit the Langmuir model and the Pseudo‐second‐order model well, respectively. Desorption was carried out in weak acid solution and 70% MB could be removed, suggesting the C‐g‐AA hydrogels had the potential for reuse. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Mixed solvent and polyacrylamide-blended ethylcellulose liquid crystals

The mesophase behaviours of mixed solvent cellulosic liquid crystal systems, ethylcellulose/acrylic acid+water (EC/AA+W), ethylcellulose/acrylic acid+glacial acetic acid (EC/AA+GAA) and of ethylcellulose/acrylic acid systems blended with a flexible polymer, polyacrylamide (PAM+EC/AA), have been studied. The critical concentrations decreased in all the systems compared with the pure EC/AA system and the morphologies were affected, but still cholesteric. The cholesteric properties varied with composition of solvent and polymers. ©1997 SCI