Banded Texture Research Articles

Solid‐State Polymerization of a Liquid Crystalline Copolyester Derived from 2,6‐Naphthalene Dicarboxylic Acid, Terephthalic Acid, 4‐Acetoxybenzoic Acid and Hydroquinone Diacetate

Solid‐state polymerization (SSP) has been applied for the synthesis of a wholly aromatic thermotropic liquid crystalline polymer derived from 4‐acetoxybenzoic acid, hydroquinone diacetate, 2,6‐naphthalene dicarboxylic acid, and terephthalic acid. The influence of various operating parameters, such as reaction temperature, reaction time, nitrogen gas flow velocity, and particle size, on the solid‐state polymerization has been studied, and the SSP products were characterized by polarized light microscope (PLM), differential scanning calorimeter (DSC), viscosity measurement, and nanoindentation test. It was found that the molar mass of the copolyester substantially increased during the SSP process, as shown by measurements of melting temperature and inherent viscosity of the product. The SSP reaction mechanism and rate are discussed with the changes of the operating parameters. Nanoindentation test shows the increase of hardness and modulus of the copolyesters, which is due to the increase of molar mass. A banded texture of the copolyesters with narrow bands was observed after SSP by using PLM.

ITO properties on anisotropic flexible transparent cellulosic substrates under different stress conditions

Cellulose derivatives have been actively investigated as flexible transparent substrates for liquid crystal display (LCD) technology. Working electronic devices deposited on flexible substrates are subject to deformation and external stress. Hydroxypropylcellulose (HPC) solid films (20–60 μm) obtained from aqueous liquid crystalline solutions present tunable topography. Substrates with anisotropic topography were obtained by casting and shearing a 65% (w/w) HPC aqueous solution (HPC-65). Two types of periodicity were observed by atomic force microscopy (AFM). A primary set of large bands, perpendicular to the shear direction (1.8–2.1 μm periodicity and 74–87 nm average peak-to-valley height) was found. A secondary smoother band texture (0.35–0.40 μm periodicity and 2.9–4.4 nm average peak-to-valley height) lies under the large bands. The resistivity of indium tin oxide (ITO), deposited on these flexible anisotropic substrates (HPC-65/ITO) under different stress conditions, was studied. These stress conditions were originated by folding the films around tubes with decreasing diameter (45–5 mm). The folding was performed along two directions. One direction was chosen with the tube axis along the shear direction (FB1). Another direction was chosen with the tube axis perpendicular to the shear direction (FB2). The resistivity of ITO films submitted to FB1 folding does not change significantly with the tube diameter, nor after release neither after overnight relaxation. The resistivity of ITO films submitted to FB2 folding increases strongly and the films become insulating for tubes with diameter lower than 10 mm. AFM measurements show that this anisotropic behavior is induced by cracks in the ITO coatings. These cracks appeared mainly along the secondary set of bands found in anisotropic substrates.

A multiscale texture analysis procedure for improved forest stand classification

Image texture is a complex visual perception. With the ever-increasing spatial resolution of remotely sensed data, the role of image texture in image classification has increased. Current approaches to image texture analysis rely on a single band of spatial information to characterize texture. This paper presents a multiscale approach to image texture where first and second-order statistical measures were derived from different sizes of processing windows and were used as additional information in a supervised classification. By using several bands of textural information processed with different window sizes (from 5×5 to 15×15) the main forest stands in the image were improved up to a maximum of 40%. A geostatistical analysis indicated that there was no single window size that would adequately characterize the range of textural conditions present in this image. A number of different statistical texture measures were compared for this image. While all of the different texture measures provided a degree of improvement (from 4 to 13% overall), the multiscale approach achieved a higher degree of classification accuracy regardless of which statistical procedure was used. When compared with single band texture measures, the level of overall improvement varied between 4 and 8%. The results indicate that this multiscale approach is an improvement over the current single band approach to analysing image texture.

Banded texture of photo-aligned azobenzene-containing side-chain liquid crystalline polymers

Poly(6-[4-(4-cyanophenylazo)phenoxy] x-methylene methacrylate) ( P x , x is 2 or 6) were synthesized and used to study the texture of side-chain liquid crystalline polymers (SCLCPs) after photoinduced orientation. With increasing temperature of irradiated P 2 film up to 125 °C, just above its T g, 123 °C, a banded texture was observed for SCLCPs under polarized optical microscope (POM). There is no banded texture of irradiated P 6 ( T g, 72 °C) film when heating to 75 °C. The formation of the banded texture is considered to be due to co-existing of in-plane and out-of-plane orientation mesogens in P 2 film, which is explained in terms of a molecular model. Based on our experimental results, factors of irradiation light intensity, film thickness, and heating rate on the formation of the banded texture were studied in this work.

Direct decoration of disclinations by solidification-induced band texture for a nematic side chain liquid crystalline polymer

For a nematic polymethacrylate side chain liquid crystalline polymer, g 154 N 298 I (°C), the solidification-induced band texture has been observed aligned along the disclination under a polarizing optical microscope, when the specimen was quenched from 280°C to room temperature. The decoration technique of solidification-induced band texture, which is usually reported for main chain liquid crystalline polymers, was then introduced to reveal the director field pattern along a disclination for this side chain liquid crystalline polymer. It was found by infra-red dichroism measurements that the director orientation is parallel with the direction of the band. On this basis, disclinations with strength s=±1/2 and s=±1 were mapped according to the corresponding pattern of solidification-induced band texture. In addition, two types of inversion wall, loop-like and splay-type walls, were also found to be decorated by the solidification-induced band texture.

Ordering-induced micro-bands in thin films of a main-chain liquid crystalline chloro-poly(aryl ether ketone)

Micro-banded textures developed from thin films of a main-chain thermotropic liquid crystalline chloro-poly(aryl ether ketone) in the melt were investigated using transmission electron microscopy (TEM), selective area electron diffraction, and atomic force microscopy techniques. The micro-banded textures were formed in the copolymer thin films after annealing at temperatures between 320 and 330 °C, where a highly ordered smectic crystalline phase is formed without mechanical shearing. The micro-banded textures displayed a sinusoidal-like periodicity with a spacing of 150 nm and an amplitude of 2 nm. The long axis of the banded texture was parallel to the b-axis of an orthorhombic unit cell. In the convex regions, the molecular chains exhibited a homeotropic alignment, i.e. the chain direction was parallel to the film normal. In the concave regions, the molecular chains possessed a tilted alignment. In addition to the effects of annealing temperatures and times, the thickness of the film played a vital role in the formation of the banded texture. A possible formation mechanism of this banded texture was also suggested and discussed. It was suggested that the micro-bands were formed during cooling.

Nonisothermal crystallization kinetics and spherulite morphology of poly(trimethylene terephthalate)

The nonisothermal melt crystallization behavior of poly(trimethylene terephthalate) (PTT) was investigated using the DSC technique. PTT peak exothermic crystallization temperature was found to move to lower temperatures as the cooling rate was increased. The modified Avrami equation exponent, n, was 4 when the cooling rates were between 5 and 15 °C/min, indicating a thermal nucleation and a three-dimensional spherical growth mechanism. When the cooling rate was increased to 25 °C/min, n gradually decreased to near 3, implying the nucleation mechanism changed to an athermal mode. PTT nonisothermal crystallization behavior could also be analyzed using the Ozawa equation and the combined equations of Ozawa and Avrami with very good fit of the data.PTT spherulite morphologies and the sign of the birefringence depended strongly on the spherulite's growth temperature. When the growth temperature was decreased from 222 to 170 °C, the spherulite changed from a saturation-type dendritic morphology to one with a colorful banded texture; the sign of the birefringence also changed in the following order: from a weakly positive spherulite→mixed spherulite→weakly negative spherulite→negative spherulite→positive spherulite→negative spherulite→positive spherulite.

Fatigue Behavior of AZ31 Extruded Magnesium Alloy in Laboratory Air

Rotating bending fatigue test was carried out using AZ31 extruded magnesium alloy in order to clarify the S-N curve, crack initiation and propagation behavior of the alloy. The mechanisms of both crack initiation and crack arrest at the grain boundary during the fatigue process were investigated in detail with a special attention to the microstructure of the material. The material is divided roughly into 2 kinds of banded texture, the phase A (white zone) and B (black zone). The phase B consists of the crystal grains (phase C). Near the endurance limit of the material, fatigue life is greatly affected by a slight difference in the stress amplitude. This feature in fatigue lives is responsible to the sharply curved S-N curve at the endurance limit, a general characteristic of the extruded magnesium alloy. The fatigue crack initiates at the upper and lower edges of the grain boundary of the phase C in the early stage of the fatigue life. At stress amplitude of 122.5 MPa which is slightly larger than the fatigue limit, the crack propagates to the next B-phase without being blocked by the grain boundary of the phase C, however at 120 MPa which is slightly less than the fatigue limit, the crack advance was blocked by the grain boundary. The sharp curved S-N curve is attributable to the crack arrest which is caused by the grain boundary of the phase C. By integrating the relationship between stress intensity factor and crack growth rate, the calculated S-N curve agrees well with the experimental result.

Shear induced molecular alignments of a side-chain liquid crystalline polyacetylene containing biphenyl mesogens

Mesomorphic properties of a side chain liquid crystalline polyacetylene, poly(11-{[(4′-heptyloxy-4-biphenylyl)carbonyl]oxy}-1-undecyne) (PA9EO7), are investigated using polarized optical microscope, X-ray diffraction, and transmission electron microscope. Polymer PA9EO7 forms enantiotropic smectic A and smectic B phases. It also exhibits an additional high order smectic phase, a sandwich structure consisting of different molecular packing of biphenyl mesogenic moieties from that of alkyl spacers and terminals, when it is prepared from its toluene solution. Shearing the polymer film at its smectic A phase generates banded texture with the alignment of the backbones parallel to the direction of shear force. While at its high order smectic phase, the mesogen pendants of the polymer are arranged parallel to the direction of shear. The different mesomorphic behaviors arise from different molecular alignments influenced by the fluidity.

Relaxation Processes in sheared films of ethyl-cyanoethyl cellulose cholesteric liquid crystalline solutions

The relaxation processes in sheared films of ethyl-cyanoethyl cellulose [(E-CE)C]/acrylic acid (AA) cholesteric liquid crystalline (LC) solutions were studied by polarizing optical microscopy (POM) and UV-Vis spectrophotometry. Under shearing normal to the helix axis and above the critical shear rate, the planar texture arrangement of the (E-CE)C/AA cholesteric LC solution was destroyed and transformed to the nematic phase. Observed by POM, the banded texture formed quickly following the cessation of the shear, but it was unstable and disappeared after several minutes. The reflection spectrum of the sheared (E-CE)C/AA cholesteric LC solution film was recorded as a function of relaxation time. It was found that the selective reflection property was lost under the shear, but the shape of the reflection spectrum recovered quickly with cessation of the shear, and the reflection peak in the spectrum became sharper with time, returning to the original form before shearing. A proposed model of the structural transformation during the relaxation was confirmed by additional optical measurement and transmission electron microscopy.

Texture evolution in hot band and annealed hot bands of low alloyed ferritic stainless steel

The texture evolution in hot band and annealed hot bands of low alloyed ferritic stainless steel with about 11 wt-%Cr was experimentally investigated using quantitative texture analysis. While the hot band texture was composed of components of α fibre and in particular δ fibre, its microstructure was a banded structure of mostly relaxed martensite and retained ferrite. Both the texture and microstructure of the hot band was derived from partially recrystallised austenite. During single phase hot band annealing, there was a strong sharpening in the strength of the texture components of δ fibre by strain induced boundary migration of the retained ferrite and formation of fine carbide sheets leading to the persistence of ferrite banding. In contrast, two phase hot band annealing resulted in the formation of a nearly equiaxed duplex ferrite grain structure with an aggregate of precipitated carbides within the transformed ferrite grains and complete elimination of microstructural banding of the hot band, and also led to the occurrence of a texture memory phenomenon.

Elastic constant anisotropy and disclination interaction in nematic polymers I. Apparent variation in anisotropy

This work presents the effect of elastic anisotropy and disclination interaction on wedge disclinations in the nematic phase of thermotropic polymers, by combining experimental measurements, (this paper part I), with numerical simulation (part II [1]). In part I, the decoration provided by spontaneous banded texture gives much information about the defect structure of polymeric nematics. Working with a semi-rigid polyester, the optical images of +1/2 disclinations revealed by banding enable the distortion to be determined as a function of polar coordinates from the cores. Continuum theory allows the apparent elastic anisotropy, ϵ , of bend and splay constants of the copolyester to be determined from the distortion measurement. The values of ϵ , are seen to vary greatly in the range −1 to +1 between different +1/2 disclinations in the same sample. The statistics of the measurement indicate that the distribution of the values of ϵ is random. The implication of these observations is that the curvature of wedge disclinations is affected not only by the elastic anisotropy of the material, but also by other factors. The possible reasons are discussed: the interaction of neighbouring disclinations has been numerically analysed to be the predominant factor in [1]. This work also implies that values of the intrinsic elastic anisotropy obtained by measuring the distortion of individual wedge disclinations must be viewed with some circumspection.

Spherulitic morphology and crystallization kinetics of melt-miscible blends of poly(3-hydroxybutyrate) with low molecular weight poly(ethylene oxide)

The spherulitic morphology and crystallization kinetics of the blends of poly(3-hydroxybutyrate) (PHB) with the low molecular weight poly(ethylene oxide) (PEO) prepared by the solution casting have been investigated by differential scanning calorimetry and polarized optical microscopy. The blend was a crystalline/amorphous system when temperatures lie between the melting point of PEO (T m PEO = ca. 60 ° C) and that of PHB (T m PHB = ca. 170 ° C), while it became a crystalline/crystalline system below T m PEO. With PHB crystallization at the crystallization temperature ( T c) of 70 °C, the blends showed PHB banded spherulitic texture, which could be perturbed by the subsequent PEO crystallization in PEO-rich compositions upon further cooling to room temperature. When PHB and PEO were allowed to crystallize upon quench from melt to room temperature, fairly competitive crystallization emerged where crystallization and segregation of PHB and PEO may occur simultaneously, leading to a complicated spherulitic morphology. As for the results of crystallization kinetics, the PHB crystallization exothermic temperature ( T f PHB ) on cooling, PHB spherulitic growth rate ( G PHB), and overall crystallization rate of PHB ( k n ) exhibited maxima in their dependences of PEO composition. This was attributed to the coupling between enhanced chain mobility and depression in equilibrium melting point ( T m 0), since the low molecular weight PEO has a very low glass transition temperature ( T g) over the T c range studied, G PHB increased with T c but k n was found to decrease. The drop of k n with increasing T c was therefore predominately governed by the large depression in nucleation rate at higher T c.

Direct decoration of disclinations by solidification-induced band texture and focal-conic texture for a low molar mass liquid crystal

Two decoration methods, solidification-induced band texture decoration and focal-conic texture decoration, were established to map the director field of disclinations in a low molar mass methacrylate liquid crystal. It was found that when the specimen film is quenched from the nematic melt to room temperature, solidification-induced band texture is observed arrayed along with the schlieren texture, and the orientation of the director field can be displayed. Moreover, when the specimen is cooled from the nematic melt to 63°C and annealed, the focal-conic texture of the smectic A phase is found to grow around the corresponding disclination core with good orientation to reveal the director field. By the two decoration techniques, the director fields of disclinations with strength s = 1/2 and s = ± 1 were revealed. Two types of inversion wall, loop-like wall and splay-type wall, were found by both solidification-induced band texture decoration and focal-conic texture decoration.

Multiordered Phase Structures Of Nematic Pbo/ppa Solution

Liquid crystalline solutions of poly (p-phenylene benzoxazole) (PBO) in polyphosphoric acid (PPA) were prepared and studied. The typical banded texture and disclination of sheared PBO/PPA solution were observed by polarizing optical microscopy (POM), and the microstructure of the periodic aligned polymer chain that induced the texture was investigated by scanning electron microscopy (SEM). Spherulite structure was found in the PBO/PPA system with little shearing. Differential scanning calorimeter (DSC) analysis on the system revealed the existence and melting behavior of two ordered phases. An exothermic peak at 85°C was interpreted as the enhancement of the interaction between PBO molecules and PPA solvent, and the endothermic peaks at 140 to 150°C and 180 to 200°C are explained as the melting of the ordered phases. The changes of small-angle light scattering (SALS) patterns of PBO/PPA solution at different temperature further supported these results.

Effect of Chemical Composition and Thermomechanical Processing on Texture in Hot Bands of Ti and Ti+Nb Containing Ultra-low Carbon Steels

The effect of carbon, Ti and Nb on the formation of hot band texture in ultra-low carbon steels was studied. The chemical compositions were selected so that two of the four steels were fully stabilized with respect to carbon and the other two were expected to have some carbon in solution under equilibrium conditions. The slab reheating temperature ranged from 1 200 to 1 280°C. The first deformation was applied with a 50% reduction to simulate the roughing pass at 1 150°C. The samples were then deformed with another 50% reduction at either 1 050 or 920°C. The crystallographic orientations of the resulting ferrite were presented in the form of so-called skeleton plots along the RD-, TD- and ND-fibers. The main texture found was the cube-on-corner, {111}‹110›, component. The rotated cube component, {001}‹110›, was also present but its intensity was always lower than the intensity of the cube-on-corner component. The presence of the cube-on-corner texture was explained by the large grain size in the starting as-cast ingots and by the heavy reductions per pass. The combination of low reheating temperature and low finishing temperature generated the highest ratio of {111}/{100}. Decreasing the carbon content from 35 to 17 ppm and adding 90 ppm Nb to a Ti-alloyed ULC steel further increased the {111}/{100} ratio.

Decoration of disclinations by solidification-induced band texture and focal-conic texture for a low-molar-mass liquid crystal

Two decoration techniques, solidificationinduced band texture decoration and focal-conic texture decoration, have been established to exhibit the director field of disclinations in a low-molar-mass methacrylate liquid crystal. The disclinations with strengths = 1÷2 ands = ± 1 are observed by the two decoration methods. For the solidificationinduced band texture decoration, the molecular orientation is perpendicular to the direction of the band. While for focalconic texture decoration, it has been proved by the results of IR dichroism that the direction of the director is parallel to the direction of the focal-conic. Therefore, the sketch map of the molecular director filed can be mapped according to the morphological pattern of the solidificationinduced band texture or focal-conic texture.

Molecular packing and morphology of oligo(m-phenylene ethynylene) foldamers.

Understanding and controlling solid-state morphologies and molecular conformations is the key to optimizing the properties of materials. As an example for the influence of small chemical changes on solid-state structures, we studied oligo(m-phenylene ethynylene) foldamers, where the introduction of an endo-methyl group induces a transition from an extended all-transoid to a helical all-cisoid conformation. The resulting structural changes were analyzed by X-ray diffraction (XRD), polarized optical microscopy (POM), and low-dose high-resolution electron microscopy (LD-HREM) over several length scales from the molecular to the mesoscopic level. The strong tendency of the endo-methyl oligomer 1 to form stable compact helices in solution resulted in round droplets with an ordered hexagonal columnar (Col(ho)) liquid crystalline structure, where shrinkage during the crystallization resulted in the formation of a banded texture. On the other hand, the endo-hydrogen oligomer 2 exhibited a very different morphology; its extended linear shape was maintained during crystallization and resulted in an extended lamellar structure, which was determined by a compromise between crystalline packing and minimization of the surface area. Another pronounced difference between both molecular structures was the ability of the extended lamellar "crystals" to bend, whereas the helices form either straight or disordered domains. In addition, both materials exhibit strong surface effects, which extend considerably inside the droplet and induce uniform bending of the supramolecular structures.

Synthesis of zoning-free BaSO4-PbSO4 solid solution and its structural characterizations

Abstract Natural Pb-bearing barite, (Ba,Pb)SO4 “hokutolite”, is a radioactive sulfate mineral occurring in hot-spring deposit. An attempt to synthesize (Ba,Pb)SO4 crystal with a flux-growth process was made in this study. BaSO4 and PbSO4 in various proportions were used as precursor materials with Na2SO4 as a flux agent. The growth was carried out in a platinum crucible at 750-850ºC and ambient pressure conditions. The nucleation and growth were activated by a slow-cooling process at 2ºC/hr cooling rate. The flux-grown (Ba,Pb)SO4 crystals up to 1 mm in dimension were obtained and their chemical compositions were found to cover the entire range between BaSO4 and PbSO4. Thus there does exist a complete solid solution series between the barite (BaSO4) and anglesite (PbSO4) binary system. This result is consistent with that reported for (Ba,Pb)SO4 synthesized with a hydrothermal method. Both natural and hydrothermally synthesized (Ba,Pb)SO4 crystals display a distinct domain structure in which the Ba/Pb ratio varied among different domains. This type of chemical zoning is recognized under an optical microscope to be a banded texture in which dark bands (Ba-rich area) alternate with bright bands (Pb-rich area). In contrast, the (Ba,Pb)SO4 samples synthesized in this work contain no detectable optical bands, and this dramatic difference is believed to be a direct consequence of different growth kinetics. The flux-grown (Ba,Pb)SO4 crystals were determined to be a barite type of structure with the Ba and Pb atoms substituting each other in a fully disordered arrangement. The cell parameters vary continuously and systematically from the Ba-rich end toward the Pb-rich end as dictated by an ideal solid solution series.

Liquid crystalline (cyanoethylpropyl)cellulose and its optically anisotropic composites with acrylic polymers

Described herein are anisotropic polymer composites, made up of (cyanoethylpropyl)cellulose (CEPC) and acrylic polymer. A band texture (which can be seen with a polarisation microscope) forms in CEPC and its lyotropic solutions in acrylic monomer after orientation as a result of relaxation phenomena. The photopolymerisation of acrylic monomer (acrylic or methacrylic acid) in an oriented lyotropic solution of CEPC ‘freezes’ the orientation, and stable birefringent polymer composites are created. Thermooptical analysis shows that these composites exhibit thermally reversible anisotropy of optical properties. Molecular relaxations in such composites were investigated by means of dielectric and mechanical spectroscopies. The molecular relaxation processes, characteristic of pure components, are preserved in these composites. Two representations were used in dielectric spectroscopy: the temperature dependences of dielectric loss ε″ and of electric modulus M″. The latter was especially useful in the high temperature range, where ionic conductivity dominates the dielectric response.