Gas transport phenomena in hydroxypropyl cellulose solid film retaining cholesteric liquid crystalline order

Two kinds of hydroxypropyl cellulose (HPC) films were prepared: one retained cholesteric liquid crystalline order (HPC-A), and another was amorphous (HPC-B). Gas transport phenomena in the HPC-A films were determined at 20°C, which is below the T_g of HPC, compared with those in the HPC-B films, by using mainly oxygen and nitrogen gases; herium and carbon dioxide gases were also used. The permeability coefficient P for the HPC-A films was smaller than that for the HPC-B films by approximately 10 times. The gas permselectivity, defined as the ratio of P for each gas, was affected by the liquid crystalline order, as follows: The permselectivity for the HPC-A films was greater than that of the HPC-B films. The trends of gas permeability and permselectivity for the liquid crystal-forming HPC films were the same as those reported for other liquid crystal-forming cellulosic films. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1465–1470, 1998     

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.     

The variation of cholesteric order during polymerization of the solvent in liquid crystalline solutions

Summary Ethyl-cyanoethyl cellulose [(E-CE)C]/acrylic acid (AA) formed a cholesteric liquid crystalline solution with vivid colors when the concentration is 42–52 wt%. (E-CE)C/polyacrylic acid (PAA) composites with cholesteric structure were prepared by polymerization of the AA in the (E-CE)C/AA liquid crystalline solutions. The layers of ordered polymer chains in the cholesteric phase were inclined during polymerization and the degree of the inclination depended on the polymerization temperature and the concentration of the solution before polymerization. Key words: Cholesteric structure, polymerization, and selective reflection. Received: 19 January 2000/Revised version: 13 March 2000/Accepted: 29 March 2000     

Structural transitions in liquid crystalline solutions of some cellulose derivatives

It was found that the domains of the mesophase of the investigated systems have cylindrical symmetry and a different direction of the maximum polarizability: for ethylcellulose and cellulose diacetate, the polarizability is directed along the axis of the cylinder, while it is at an angle of 45‡ for hydroxypropylcellulose. Formation of liquid-crystalline spherulites in the thermotropic transition of isotropic solutions of ethylcellulose in formic acid to the mesophase was demonstrated. In the liquid crystal—isotropic liquid phase transition, a characteristic extreme of the intensity of light scattering is observed near the region of melting of the liquid crystalline matrix, so that this method can be used for identifying the region of the existence of a two-phase “corridor”. Translated from Khimicheskie Volokna, No. 5, pp. 25–27, September–October, 1997.     

Permeability of oxygen and nitrogen gases in ethyl cellulose solid films retaining cholesteric liquid crystalline order

Ethyl cellulose (EC) films that retain lyotropic and thermotropic cholesteric liquid crystalline order, and an amorphous EC film were prepared. The liquid crystalline order was identified by optical measurements. The comparative permeability of oxygen and nitrogen gases for three kinds of EC film was determined, and the applicability of the EC films that retained cholesteric liquid crystalline order to oxygen enrichment are discussed. The permeability of oxygen or nitrogen gas for the liquid crystalline films was lower than that for the amorphous ones. The activation energy for the permeability coefficient of oxygen gas was ca. 3.5 kcal/mol. The ratio of permeability coefficient for oxygen gas to that for nitrogen gas was less than 4. Interestingly, the permselectivity of oxygen and nitrogen gases for the liquid crystalline films was greater than that for the amorphous ones. © 1996 John Wiley & Sons, Inc.     

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.     

Preparation and mechanical properties of chemically cross-linked hydroxypropyl cellulose solid films retaining cholesteric liquid crystalline order

Hydroxypropyl cellulose films were cast from liquid crystalline solutions with a crosslinking agent. The solubility test and the optical measurements of the resultant films were performed. The tensile, dynamic mechanical, and creep properties of the films were determined. The data of solubility in water determined that the cast films are cross-linked, and the data of circular dichroism spectra, that the cast films retain the cholesteric liquid crystalline order (right-handed sense). Both findings clarified that the cast films retain the cholesteric order fixed by cross-linking. The cross-linking depended on the pairs of the solvent–cross-linking agent. The mechanical properties also depended on the pairs: the tensile strength and moduli did not always increase with cross-linking. The creep resistance improved with cross-linking. The thermally activated Eyring process could be applied and the activated volumes were evaluated for water- and methanol-cast films. There were not clear phenomenological correlations between the mechanical properties of our films.     

Birefringence of a polymeric cholesteric liquid crystal measured by refractometry

The Abbé refractometer provides a convenient way to measure the refractive indices and birefringence of polymeric liquid crystalline solutions. The cholesteric mesophase formed by (acetoxypropyl) cellulose and its solutions in dibutyl phthalate were examined at 26°C and 50°C. The measured refractive indices were dependent on the direction of shear when the polymer was applied to the refractometer plates. The initial shear-induced nematic-like order relaxed slowly to the equilibrium planar cholesteric structure. The refractive index for the isotropic solutions and the two refractive indices for the anisotropic solutions all varied linearly with polymer concentration, and the width of the intermediate two-phase region was readily determined. The changes in refractive index with polymer concentration and with orientation on the refractometer plate were rationalized with a simple model of the cellulosic mesophase, and an order parameter of 0.7 was estimated. The layer birefringence calculated from optical rotatory dispersion measurements of the cholesteric reflection band intensity was in good agreement with the birefringence measurements.     

Swelling behavior of crosslinked hydroxypropyl cellulose films retaining cholesteric liquid crystalline order. I. Effect of temperature

Temperature dependence of the swelling behavior in both water and propanol was determined for the crosslinked hydroxypropyl cellulose (HPC) films retaining cholesteric liquid crystalline order (CLCO) and for the crosslinked amorphous HPC films. The dependence of swelling behavior in water for the films retaining CLCO was different from that of the amorphous films. With increasing temperature, the equilibrium swelling ratio (B_e) for the films retaining CLCO decreased, whereas B_e for the amorphous films increased. In propanol, both films exhibited the same temperature dependence. B_e increased with increasing temperature. The increasing rate of the swelling in transient state showed similar temperature dependence on B_e. The increasing rate for the films retaining CLCO decreased with temperature, but that for the amorphous films increased in water; in propanol, the increasing rate for two types of films increased. The difference in the swelling behavior between the two types of films may be due to the difference in the number-average molecular weight between crosslinks. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1015–1022, 1999     

Characteristics of the liquid crystalline state of cellulose derivatives

The effect of external factors on the structure of semi-stiff-chain polymers of the cellulose derivatives class is discussed. New methods of investigation are reported, where uniaxial flow of the polymer with constant stresses and temperature and mechanical orientation of the ferromagnetic filler along the lines of force of a homogeneous magnetic field during formation of chain structures were used as the external effects. The results of an analysis with optical methods indicate the ability of the polymers investigated to form a more ordered type of mesophase in the given conditions than is characteristic of them.Moscow State Academy of Applied Biotechnology. Translated from Khimicheskie Volokna. No. 3, pp. 15–17, May–June, 1996.     

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.     

The cholesteric nature of cellulose triacetate solutions

Solutions of cellulose triacetate (CTA) in trifluoroacetic acid (TFA) become liquid crystalline above a certain critical concentration. Using the techniques of spectrophotometry, wide-angle light scattering and circular dichroism we have shown that the mesophase formed is cholesteric. We have measured its pitch, which depends on polymer concentration, and shown that the cholesteric structure is right-handed. Measurements of optical activity and the optical effects of shear and magnetic fields are also described and discussed.     

Synthesis and characterization of novel liquid crystalline cholesteryl-modified hydroxypropyl cellulose derivatives

Two new series of cholesteryl-modified hydroxypropyl cellulose (HPC) derivatives were synthesized by performing reactions involving HPC, a cholesterol-based mesogenic dimer (HPC-G1-Chol), or cholesteryl chloroformate (HPC-Chol), all with different degrees of substitution (D _Chol). All of the compounds obtained were characterized by conventional spectroscopic methods. The D _Chol values of the modified HPCs was obtained using ¹H NMR spectroscopy. Thermogravimetric analysis and differential scanning calorimetry (DSC) in combination with polarizing optical microscopy (POM) were used to investigate the thermal properties of the compounds obtained. The glass transitions of the modified HPCs occurred at lower temperatures than the glass transition temperature for HPC, but the glass transition temperatures increased with increasing D _Chol. All of the synthesized polymers formed thermotropic liquid crystalline phases. Polymers with a mesogenic side chain (i.e., the HPC-G1-Chol series) had wider mesophases than HPC and polymers that were derived from HPC-Chol. These compounds were found to be soluble in a variety of organic solvents, so they formed lyotropic liquid crystal mesophases in acetone. The critical concentrations above which liquid crystalline order was observed were 20 and 25 wt% for a sample from each series (HPC-G1-Chol and HPC-Chol, respectively) in acetone. It can therefore be hypothesized that HPC-G1-Chol has a greater propensity to exhibit specific chain–chain association phenomena than HPC-Chol in acetone.     

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.     

Effect of addition of cellulose powder on the viscometric behavior of liquid crystalline solutions of ethyl cellulose in m-cresol

Steady-state shear viscosity for the liquid crystalline ethyl cellulose solution filled with cellulose powders was determined using a cone-plate-type viscometer and the effects of cellulose powder content, powder aspect ratio and temperature on the viscometric behavior and phase transformation were discussed. The addition of powder increased the viscosity and decreased the activation energy (E_a) for flow, but did not affect the phase transformation. The viscosity and E_a depended on the aspect ratio; with greater aspect ratio, the viscosity enhancement was accelerated and E_a as well as the decrease in E_a with powder content increased. The phase transformation did not depend on the aspect ratio, the dependences of viscosity and of E_a on powder content depended on the solution phase; the dependences for the anisotropic phase were smaller than those for the isotropic one. The findings appeared to originate from the alignments of powders and rod-like molecules.     

Dynamic viscoelastic behavior of cholesteric liquid crystalline side-chain copolymers

Summary The rheological behavior of the cholesteric side-chain copolysiloxane whose two kinds of mesogenic groups consist of cholesteryl units and biphenyl benzoate units was investigated for three different compositions: 31:69, 35:65, 37:63 (in mol%). On the frequency dependence diagram of G′ for the copolymers at various temperatures, G′ decreases with decreasing frequency. The slope of G′ in a higher frequency region at lower temperatures (110°–130°C) is similar to that in the flow region of amorphous polymer melts. However, the slope of G′ in a lower frequency region at higher temperatures (140°–160°C) is relatively small, and the G′ curves in this region can not be superposed on to a single master curve. This deviation seems to be due to change in stability of the domain structure of the cholesteric phase. Furthermore, on the temperature dependence curve of G′, G′ showed a maximum near T _c1 . This maximum of G′ curve seems to be caused by molecular organization of a blue phase.     

VIscometric behaviour of Kevlar fibre filled liquid crystalline solutions of ethyl cellulose in m-cresol

Liquid crystalline solutions of ethyl cellulose in m-cresol were mixed with Kevlar® fibres, and the viscometric behaviour with respect to temperature of those filled systems was determined with a cone-plate type viscometer. The viscosity of the systems exhibited a maximum and a minimum at temperatures denoted by T_max and T_min' respectively. The effects of fibre on the critical temperatures (T_max and T_min) and critical concentrations (C_a and C_b) and on the viscosity enhancement are discussed. T_max and T_min decreased with fibre concentration for single-phase anisotropic solutions, whereas they increased for the biphasic solution. The critical concentrations increased with fibre concentration and C_b was more sensitive to the fibre than C_a. The viscosity enhancement due to the fibre depended on the phase of solution. In the single-phase (isotropic and anisotropic), the viscosity enhanced with fibre; however, in the biphasic solution, the effect was not simple. The viscosity enhancement for the single-phase anisotropic solutions with fibre was lower than that for the isotropic solutions.