Liquid Crystalline Cellulose Derivatives Research Articles

Compatibility–structural color property relationship of binary blends of acetylated hydroxypropyl celluloses with different degrees of acetylation

AbstractPolymer blends containing liquid crystalline cellulose derivatives potentially enable the fabrication of optical functional materials because of their unique optical properties, that is, structural color and circular dichroism. However, studies on the effect of the compatibility of the components on the optical properties of such blends are scarce, even though component compatibility is a crucial factor for the physical properties of the polymer blends. In this study, we investigated the effect of the component compatibility on the structural color property of binary blends of acetylated hydroxypropyl celluloses (AHPCs) with different degrees of acetylation (DSAc). The spectroscopic analyses of the AHPC blends revealed that the structural color of blends with a small DSAc gap between AHPC components systematically changed with the blend composition, whereas the color of blends with a large DSAc gap was independent of the composition. Compatibility tests via spin–lattice relaxation time measurements using solid‐state nuclear magnetic resonance indicated that the different composition dependence of the color was attributed to the compatibility of the components, which varied according to the DSAc gap.

Facile design of pressure-sensing color films of liquid crystalline cellulosic/synthetic polymer composites that function at desired temperatures

We have developed a facile method for material design of pressure-sensing films for various operating temperatures using cholesteric liquid crystalline (ChLC) cellulose derivatives. A series of acetylated hydroxypropyl celluloses (AHPCs) with different degrees of acetylation (DSAc) was prepared and their concentrated solutions in monomeric solvents showed coloration based on the selective reflection of ChLC. The critical coloration concentration of the AHPC/monomer solutions decreased with increasing DSAc because the twist angle of the cholesteric helix increased by introducing acetyl groups. The ChLC solutions were subsequently subjected to in situ polymerization to immobilize the ChLC structure in the produced composites. The ChLC structure was well immobilized in the composites with moderate compatibility between the component polymers. The obtained AHPC/polymer ChLC composites exhibited compression-induced mechanochromism, and consistent pressure sensitivity was achieved at various temperatures by selection of the counter polymer species. This approach is applicable for designing pressure-sensing films tailored to the operating temperature.

ヒドロキシプロピルセルロースへの置換基の導入による液晶材料化<br/>—熱的性質および配向挙動—

Novel thermotropic liquid-crystalline cellulose derivatives were synthesized by the addition reaction of hydroxypropylcellulose with isocyanate. The liquid-crystalline cellulose derivatives exhibited columnar mesophases on heating and cooling. The cellulose derivatives formed a water-absorbing resin and their resinous gel films showed water-absorbency and stability with time. The resin plates of the cellulose derivatives were obtained by a hot press process at liquid-crystalline temperatures. They showed a tensile strength that was stronger than that of polypropylene.

High Optical Quality Films of Liquid Crystalline Cellulose Derivatives in Acrylates

Cholesteric liquid crystals based on polymers are attractive because of their film‐forming properties. However, their optical properties (sharpness and directionality of the selective reflection) are usually lower than low molar mass compounds because of a polydomain structure and an angular distribution of the helix axes. In this work, cholesteric films made of liquid crystalline cellulose derivatives with improved optical properties are prepared. The careful choice of the solvent, hydrogen bond influencing additives, the synthetic realization of a very high degree of substitution on the cellulosic poly­mer, and the use of mechanical stirring in combination with a tuned substrate treatment and film‐preparation method and subsequent polymerization allow the fabrication of free standing cholesteric films of high optical quality. They show selective reflection with a half width of only 25 nm and nearly only perpendicular reflection. In addition, a method is developed by which fluorescent dyes can be introduced into the films after their preparation. image

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.

Pressure–volume–temperature results and pressure dependency on the viscosity of three liquid crystalline cellulose derivatives

The combined analyses of pressure–volume–temperature tests and oscillatory flow measurements for three thermotropic liquid crystalline cellulose derivatives, one acetoxypropylcellulose and two hydroxypropylcelluloses, are presented. This combined analysis allows for the determination of the pressure–viscosity coefficient b = ∂lnη0/∂P. It was observed that the activation energy of flow, dT g /dP, the compressibility coefficient and the pressure–viscosity coefficient obtained for the investigated thermotropic systems lie within the range of the values of these parameters reported for conventional polymers. However, the values of the thermal expansion coefficient below T g are considerably lower, reflecting the effect of the liquid crystalline order. The differences found between the three systems are explained considering microstructural factors, such as (average molar substitution), length of branching and hydrogen bonds.

How to mimic the shapes of plant tendrils on the nano and microscale: spirals and helices of electrospun liquid crystalline cellulose derivatives

We show that suspended nano and microfibres electrospun from liquid crystalline cellulosic solutions will curl into spirals if they are supported at just one end, or, if they are supported at both ends, will twist into a helix of one handedness over half of its length and of the opposite handedness over the other half, the two halves being connected by a short straight section. This latter phenomenon, known as perversion, is a consequence of the intrinsic curvature of the fibres and of a topological conservation law. Furthermore, agreement between theory and experiment can only be achieved if account is taken of the intrinsic torsion of the fibres. Precisely the same behaviour is known to be exhibited by the tendrils of climbing plants such as Passiflora edulis, albeit on a lengthscale of millimetres, i.e., three to four orders of magnitude larger than in our fibres. This suggests that the same basic, coarse-grained physical model is applicable across a range of lengthscales.

Determination of the molecular orientation in the polymeric liquid crystalline systems by low frequency Raman spectroscopy

Anisotropic polymer composites with fixed, oriented liquid crystalline organisation prepared by in situ photopolymerisation of acrylic or methacrylic acids in several cellulose derivatives were investigated by low frequency Raman scattering. The results were interpreted basing on a model of non-continuous structure of polymer glasses. The Raman investigations have shown that the macromolecules of the non-mesogenic (acrylic) component are oriented in the anisotropic composites, and that the orientation of the polyacrylic chains is more pronounced in the composites with higher concentration of the liquid crystalline cellulose derivative. It was found, that the interactions between the components play a crucial role in the formation of the composites (template-like photopolymerisation) and they determine their supramolecular structure. The liquid crystalline cellulose derivatives able to form hydrogen bonds play a role of specific cross-linking agents, while the cellulose derivatives with aliphatic side chains work as plasticisers.

Blending as a method of tuning reflection wavelength and helical twisting sense in films and composites of liquid crystalline cellulose derivatives

Ethyl cellulose (EC) with a degree of substitution of 2.41 and a fully acetylated sample (AEC) of this material, form lyotropic liquid crystalline solutions in chloroform and acrylic acid. Above 35 wt% polymer, the solutions exhibit chiral nematic phases that reflect light selectively at a specific wavelength λ 0. For EC solutions the helical twist sense of the chiral nematic phase is left handed, whereas the AEC solutions are right handed. The λ 0 and handedness of the system can be tuned to a given set of values by preparing solutions of EC and AEC in different blend ratios. These can be converted to films or composites, that retain the chiral nematic structure and the corresponding chiro-optical properties, by either casting from chloroform or photopolymerising the (EC+AEC)/acrylic acid solutions to form blend composites of EC/AEC in poly(acrylic acid). The most effective way to control the chiro-optical properties of the dry films was to use the photopolymerisation technique to form composite films of the blends. Such films can be used either as coatings to reflect visible light of a particular colour, or act as a protective layer to reduce UV degradation.

Lyotropic liquid crystalline cellulose derivatives in blends and molecular composites

Solutions of cellulose tricarbanilate (CTC) in methyl acrylate (MA) and methyl methacrylate (MMA) were prepared. The MA and MMA monomers were subsequently polymerised to produce a series of molecular composites, in which the amount of CTC and the degree of substitution (DS) of the tricarbanilate groups were varied. The CTC solutions were studied using polarised microscopy and indicated isotropic behaviour in solutions with a CTC concentration of less than 33 wt%. Solutions of 33–45 wt% CTC were found to have a nematic texture and a chiral nematic texture was detected on shearing of 45 wt% solutions. The mechanical properties and morphologies of the composites were investigated using dynamic mechanical thermal analysis (DMTA), tensile testing and scanning electron microscopy. Tensile testing measurements illustrated the reinforcing behaviour of the CTC on the composite, with the initial modulus increasing by up to 250% at 45 wt% CTC. Scanning electron microscope (SEM) micrographs for composites with <45 wt% CTC revealed a one-phase system. DMTA measurements indicated the existence of a double T g at DS of the tricarbanilate of less than 3, with a single T g for composites containing cellulose with degrees of carbanilate substitution equal to 3. The 45 wt% CTC composite showed a broad relaxation process at 350 K and another relaxation at higher temperature (490 K) corresponding to the glass transition of the CTC itself. This result, which is indicative of phase separation, is consistent with the SEM micrographs showing distinctive layered structures within the film.

Molecular relaxations in the composites of liquid crystalline cellulose derivatives with poly(acrylic acid)

The molecular relaxation phenomena of the specific polymer composites obtained by photopolymerisation of the oriented lyotropic liquid-crystalline systems composed of cellulose derivatives dissolved in photo-polymerisable acrylic acid are studied. We have investigated the composites based on two cellulose derivatives, which differ by the length of their side-chains and consequently by their physical properties.In this work, the molecular relaxations of such aniso- tropic composites were studied by dielectric relaxation spectroscopy and by thermooptical analysis. In the dielectric relaxation spectroscopy two representations were analysed: temperature dependences of dielectric loss ϵ“(T) and of electric modulus M“(T). The electric modulus representation is especially convenient to monitor the relaxations in a high temperature range where the ionic conductivity dominates the dielectric response.

Lyotropic liquid crystalline cellulose derivatives in blends and molecular composites

Macromolecular SymposiaVolume 152, Issue 1 p. 107-116 Article Lyotropic liquid crystalline cellulose derivatives in blends and molecular composites J.M.G. Cowie, J.M.G. CowieSearch for more papers by this authorValeria Arrighi, Valeria ArrighiSearch for more papers by this authorJuliet Cameron, Juliet CameronSearch for more papers by this authorDean Robson, Dean RobsonSearch for more papers by this author J.M.G. Cowie, J.M.G. CowieSearch for more papers by this authorValeria Arrighi, Valeria ArrighiSearch for more papers by this authorJuliet Cameron, Juliet CameronSearch for more papers by this authorDean Robson, Dean RobsonSearch for more papers by this author First published: 21 December 2000 https://doi.org/10.1002/1521-3900(200003)152:1<107::AID-MASY107>3.0.CO;2-ECitations: 4AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume152, Issue1March 2000Pages 107-116 RelatedInformation

The anisotropy of poly(acrylic acid) in composites with liquid crystalline cellulose derivatives as seen by low-frequency Raman spectroscopy

The low-frequency Raman scattering (LFRS) was used in order to determine the orientation of poly(acrylic acid) in anisotropy composite with liquid crystalline [(propionyloxy)propyl]cellulose (PPC). The photopolymerisation of acrylic acid in the presence of PPC leads to the formation of the poly(acrylic acid) (pAA) anisotropic network. This anisotropy is stable even at temperatures higher than the temperature of the optical isotropisation of the PPC/pAA composite. The comparison of the LFRS and thermooptical data proves the hypothesis explaining of the reversibility of the optical birefringence in the PPC/pAA composites by formation, in a course of photopolymerisation of anisotropic pAA network.

Anisotropic mesogenic liquid crystalline cellulose derivatives as a basis for functional materials

Liquid crystalline cellulose derivatives are promising materials which can be used for the formation of novel functional systems. Microcrystallites were obtained from cellulose fibers which were complexed with Fe(III) according to known methods. Dispersions of these crystallites were mixed with liquid crystalline (hydroxypropyl)cellulose and fixed in an oriented state by photopolymerization of polymerizable lyotropic solvent. The solid anisotropic polymeric networks exhibit high stability of orientation. These systems containing an organized iron complex of liquid crystalline cellulose may have new functional properties expected for dispersed metals or metal oxides in polymeric matrices. © 1998 John Wiley & Sons, Ltd.

Anisotropic mesogenic liquid crystalline cellulose derivatives as a basis for functional materials

Liquid crystalline cellulose derivatives are promising materials which can be used for the formation of novel functional systems. Microcrystallites were obtained from cellulose fibers which were complexed with Fe(III) according to known methods. Dispersions of these crystallites were mixed with liquid crystalline (hydroxypropyl)cellulose and fixed in an oriented state by photopolymerization of polymerizable lyotropic solvent. The solid anisotropic polymeric networks exhibit high stability of orientation. These systems containing an organized iron complex of liquid crystalline cellulose may have new functional properties expected for dispersed metals or metal oxides in polymeric matrices. © 1998 John Wiley & Sons, Ltd.

α-Relaxation processes in the composites of LC-cellulose derivatives

Molecular relaxation processes in the liquid crystalline cellulose derivatives (CDs) and in their composites were studied by dielectric spectroscopy. The composites, which are anisotropic polymer networks, were prepared by photopolymerization of acrylic acid in the oriented lyotropic solutions of cellulose derivatives. The investigated composites comprise poly(acrylic acid) and hydroxy-, propionyloxy-, hexanoyloxy-, or cyanoethyl-propyl cellulose. In these systems different types of intermolecular interactions are possible: hydrogen bonds, dispersive, or dipolar interactions. The temperature dependences of the α-relaxations of CDs can be fitted by the WLF equation, while the β-relaxation of poly(acrylic acid) is described by an Arrhenius function. The molecular relaxations in the composites are affected in different way by different intermolecular interactions, depending on the chemical structure of CDs.

Dynamic Viscoelasticity of Thermotropic Liquid Crystalline Cellulose Derivatives

Dynamic measurements were made on two thermotropic liquid crystalline cellulose derivatives abbreviated as HEC-C5 and TBC. HEC-C5 is a hydroxyethyl cellulose (HEC) fully acylated with pentanoic acid. Since the chemical structure of the HEC is disordered (DS=1.5 and MS=3.0), that of the tripentanoate also becomes disordered. TBC is a tri-O-β-butoxyethyl cellulose, fully etherified cellulose (DS=MS=3.0) having an ordered structure. In both samples, the temperature dependence as well as the frequency dependence of the dynamic viscoelastic functions clearly and unambiguously reflected the three states of the polymers, i.e., an anisotropic liquid, isotropic liquid, and anisotropic/isotropic co-existing state. TBC was found to undergo an anisotropic-to-isotropic transition in a very narrow temperature span (less than 10°C), the dynamic viscosity η′ increasing by a factor about 10 in this temperature span. Moreover, the temperature dependence of η′ of TBC measured at a constant frequency showed two characteristic temperatures, other than the anisotropic-to-isotropic transition temperature, which indicated certain structural changes in this polymer in the liquid crystalline state. No such detailed information was obtained from the η′-temperature diagram of HEC-C5, which showed only a very broad anisotropic/isotropic co-existing region extending from about 90°C to 145°C. These marked differences in the transition and other behavior between the two polymers are believed to originate from their difference in chemical structural order.