Thermotropic Cellulose Derivatives Research Articles

Cellulose-Based Liquid Crystalline Photoresponsive Films with Tunable Surface Wettability

We report on a new type of liquid crystalline cellulosic films with light controllable reversible wettability. The films are prepared from a thermotropic cellulose derivative functionalized with azo-containing groups. These groups exhibit dynamic changes in interfacial properties in response to UV irradiation. The UV irradiation induces trans-to-cis isomerization in the azobenzene moiety, which causes a conformational change in the upper molecular layers of the thin films. These changes originate a hydrophobic to comparatively hydrophilic transformation of the surface. The reversible wettability of the surface results from the cis/trans photo and thermal isomerization. The UV-vis absorption spectra, as well as contact angle measurements with UV irradiation, clearly support the understanding of the phenomenon. This type of surface design enables the amplification of molecular level conformational transitions to macroscopic changes in interface properties using the means of isomerism. This opens new opportunities in surface engineering using eco-friendly cellulose manipulation.

Melt spinning of thermotropic cellulose derivatives

The melt spinning of two thermotropic cellulose derivatives—trimethyl silyl cellulose and phenyl acetoxy cellulose—is described in this article. Removal of the substituents was facile, rapid, and essentially complete. Both the melt-spun and regenerated fibers had banded textures typical of fibers spun from a liquid crystalline phase. The regenerated cellulose fibers had high strengths and moduli compared to viscose rayon and Lyocel cellulose fibers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 418–423, 2000

Melt spinning of thermotropic cellulose derivatives

The melt spinning of two thermotropic cellulose derivatives—trimethyl silyl cellulose and phenyl acetoxy cellulose—is described in this article. Removal of the substituents was facile, rapid, and essentially complete. Both the melt-spun and regenerated fibers had banded textures typical of fibers spun from a liquid crystalline phase. The regenerated cellulose fibers had high strengths and moduli compared to viscose rayon and Lyocel cellulose fibers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 418–423, 2000

Shear induced textures of thermotropic acetoxypropylcellulose

Acetoxypropylcellulose is a thermotropic cellulose derivative which is cholesteric from below room temperature up to 170 °C. Its textures during and after shear flow were studied by optical microscopy and small-angle light scattering (SALS) light scattering. The main features are similar to those occurring in hydroxypropylcellulose solutions, i.e., a polydomain texture evolving into a striated texture, as seen by optical microscopy. Elliptical or else four lobes with a streak are seen in the SALS patterns. Defects appearing as short dark lines not aligned with the flow direction are shown to be responsible for the existence of the four lobes of the SALS patterns. In addition these defects seem to be located where the band texture develops during relaxation.

Thermotropic cellulose derivatives with flexible substituents IV. Columnar liquid crystals from ester-type derivatives of cellulose

Abstract Cellulose tri-n-alkanoates, fully substituted ester-type derivatives of cellulose, having acyl groups with n carbon atoms (3 < n < 18), are prepared and their thermal behaviour studied. It is found that samples of cellulose tri-n-alkanoates with n > form a novel thermotropic mesophase, characterized by a low birefringence and an extremely high viscosity compared with those of cholesteric mesophases of ether-type derivatives. Photomicroscopic, differential scanning calorimetry, and X-ray diffraction studies indicate that the mesophase formed by the cellulose tri-n-alkanoates is of a hexagonal columnar type in which two polymer chains are included in one hexagonal lattice. Two possible packing structures, resembling direct and inverse hexagonal phases of amphiphilic molecular systems, are proposed and discussed in relation to the chemical structure of the polymer.

Thermotropic cellulose derivatives blended with low-mass molecules.

Tri-O-decyl cellulose, a thermotropic liquid crystal polymer with a cholesteric structure, was blended with n-hexadecane (HD) at various concentrations and studied with its thermal and structural properties. The phase diagram of this blend system was characterized by four regions, i.e., an isotropic liquid phase (I), an anisotropic liquid phase (A), an A/I coexisting phase, and a phase including solid HD

Thermotropic cellulose derivatives with flexible substituents. III. Temperature dependence of cholesteric pitches exhibiting a cholesteric sense inversion

Abstract For the thermotropic cholesteric mesophase of tri-o-(β-methoxyethoxy)ethyl cellulose (DP = 11), cholesteric pitches larger than 2 μm were precisely determined by microscopic observation and their temperature dependence was examined in the temperature range from 80°C to 140°C. In the initial temperature region of 80°C to 106°C, the pitch increases with increasing temperature. After the pitch diverges at 106°C, it decreases as temperature is raised further. This anomalous temperature dependence of pitch was associated with a thermally-induced inversion from right- to left-handed helicoidal structure which was first observed in this kind of cellulose derivatives.

Thermotropic Cellulose Derivatives with Flexible Substituents. I. Preparation of Tri-o-(β-methoxyethoxy)ethyl Cellulose and its Cholesteric Mesophase Properties

Abstract Tri-o-(β-methoxyethoxy)ethyl cellulose was prepared by reacting the regenerated cellulose with 2-(2-methoxyethoxy)ethyl iodide and characterized as a fully substituted derivative. The resultant derivative forms a thermotropic liquid crystal in the wide temperature range from room temperature to the isotropization temperature of 180°C, showing that the (methoxyethoxy)ethyl side-chain substituent is long and flexible enough to inhibit crystallization of the extended cellulose chains and facilitate formation of liquid crystals. This is the first example of a thermotropic liquid crystalline cellulose derivative with a homogeneous side chain. This type of liquid crystal is cholesteric with a right-handed helical structure. The cholesteric pitch increases with increasing temperature, with the magnitudes comparable to the wavelength of visible light in the temperature range below 120°C.

Thermotropic cellulose derivatives with flexible substituents

Three kinds of fully substituted cellulose derivatives, cellulose triheptanoate (CTH), tri-O-heptyl cellulose (THC) and tri-O-2-butoxyethyl cellulose (TBC) were prepared. These polymers, having a side chain of similar length but of differing chemical structure, were found to show significantly different therraotropic behavior: TBC forms a cholesteric liquid crystalline phase at temperatures between 50 °C and 165 °C, the cholesteric pitch covering the region of visible lights. THC also displays a cholestric structure at temperatures between 80 °C and 130 °C with pitches on the order of several micrometers. CTH appears to show liquid crystallinity only in a very limited temperature range around 100 °C.

Optical properties of a shear‐deformed thermotropic cellulose derivative

AbstractThe band texture of a thermotropic cellulose derivative, trifluoroacetoxypropylcellulose, was studied by optical microscopy. The texture consists of parallel, long, thin, black lines when viewed between crossed polarizers with one polarizer parallel to the shear direction. These lines are perpendicular to the shear direction. Their optical properties indicate that the molecules are cooperatively oriented and this orientation director alternates from 0° to ±45° from the shear direction, with most of them at ±45°. This band phenomenon is identical to that observed with thermotropic nematic copolyesters.

Phase studies of a liquid crystalline polymer: hydroxypropyl cellulose

Phase diagrams for the isotropic-anisotropic phase transition in solutions of a thermotropic cellulose derivative, hydroxypropyl cellulose are presented. The effect of the molecular weight is demonstrated. A comparison to the theory of semi-rigid liquid crystalline polymers is given.