Banded Texture Research Articles

Oriented and low‐density tin dioxide film by sol–gel mineralizing tin‐contained hydroxypropyl cellulose lyotropic liquid crystal for laser‐induced extreme ultraviolet emission

AbstractA series of tin‐doped hydroxypropyl cellulose (HPC) lyotropic liquid crystal (LC) was synthesized using a simple process and their properties were characterized using selective reflection, wide‐angle X‐ray diffraction (WAXD), and the band texture observed under polarized optical microscope. The present preparation is applicable for mass production using large substrate with low cost HPC. A cholesteric lyotropic LC phase was observed for the hybrid solution with higher than 40 wt % HPC. After sol–gel condensation, the HPC‐Sn hybrid LC films were calcined at 400 °C and the as‐prepared product was determined to obtain tin dioxide (SnO2) which was characterized using WAXD. The iridescent color and ∼2 nm structure seen after the condensation disappeared in the as‐prepared SnO2. Scanning electronic microscope images of the SnO2 showed that the HPC content in the HPC‐Sn hybrid played an important role in controlling the SnO2 morphology. A spectrum of relatively monochromatic extreme ultraviolet (13.5 nm) emission was measured in the as‐prepared SnO2 in comparison with bulk tin and inverse opal SnO2. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4566–4576, 2009

Basaltic ignimbrite-like rocks on Saikhan Volcano, northeastern Khangai, Mongolia: Mineralogic and geochemical evidence

Rocks having a pseudofluidal ignimbrite texture have been found on Saikhan Volcano in northeast- ern Khangai, Mongolia. The rocks have a typically nodular banded texture. The fiamme and the bands vary in width between a few millimeters to a few centimeters. These rocks have the same bulk composition as trachy- basalts and do not differ from the ordinary trachybasalts found on this volcano in the form of dikes and lavas. The difference consists in the composition of glasses and minerals, as well as in the concentration of CO 2 (which is higher in the ignimbrite-like rocks). The glasses in the ignimbrite-like rocks show a trend from basal- tic trachyandesites to tephriphonolites and foidites, thus indicating the liquidus crystallization of clinopyroxene. The glasses in the lavas and dikes have a trachyte composition, indicating a residual origin following the crys- tallization of olivine and Ti-magnetite. Much of the pyroxenes (~20%) in the ignimbrite-like rocks show calcu- lated pressures during their generation to have been in the range of 6.5-14 kbars, while all pyroxenes in the ordinary lavas and dikes crystallized at pressures below 0.3 kbars. It thus follows that the magmas that have produced the ignimbrite-like rocks began crystallizing in the subcrustal magma chamber under fluid-saturated conditions, whence they were rapidly transported to the surface.

New data on the structure and composition of stromatolite buildups (Northern Anabar Region)

Lamination, a characteristic feature of stromatolites, is related to thin alternation of mineral and organogenic layers. The present paper is devoted to structures of Lower Riphean stromatolites in the Fomich River area (northern Anabar Uplift) that were described for the first time and studied with an electron microscope. Two Colonnella forms with different microstructures were examined. It has been established that a banded texture is observed if an organogenic layer is mainly composed of tightclusters of filiform (theread like) particles. However, a clotted texture is recorded if the layer is represented by isolated coccomorphic (rounded) particles. The chemical composition of these tiny structures, which can accumulate several elements, is discussed and analyzed. In the past, the organogenic layer represented a biofilm that comprised a complex-function cyanobacterial community.

Texture Evolution in a Warm-Rolled Ti-IF Steel During Cold Rolling and Annealing

The texture characteristics of a Ti-IF steel in ferritic hot-rolled (warm-rolled), cold-rolled, and annealed status were studied. The hot bands were obtained by finish rolling in ferrite region, coiling at very low temperature, and then directly annealing in industrial trial. It was found that $$ \left\{ {00 1} \right\}\left\langle { 1 10} \right\rangle $$ dominates at the surface and $$ \left\{ { 1 1 1} \right\}\left\langle { 1 1 2} \right\rangle $$ is the main component at the midsection in the hot band. The α-fiber at the surface as well as at the midsection intensifies during cold rolling and weakens during annealing, while the changing of γ-fiber depends on the hot band texture during cold rolling, but it absolutely intensifies after a well-advanced state of annealing. Orientations concentrate on $$ \left\{ {00 1} \right\}\left\langle { 1 10} \right\rangle $$ increasingly at the surface and continuously rotate to RD-fiber at the midsection as the reduction increases. The average plastic strain ratio, elongation, and strain hardening exponent measured for the cold-rolled and annealed steel increased with improving annealing temperatures.

Study on the crystal morphology and melting behavior of isothermally crystallized composites of short carbon fiber and poly(trimethylene terephthalate)

The spherulites of the short carbon fiber(SCF)/poly (trimethylene terephthalate) (PTT) composites formed in limited space at designed temperatures, and their melting behaviors were studied by the polarized optical microscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM), respectively. The results suggest that SCF content, isothermal crystallization temperatures, and the film thicknesses influence the crystal morphology of the composites. The dimension of the spherulites is decreased with increasing SCF content, but whether banded or nonbanded spherulites will form in the composites is not dependent on SCF content. However, the crystal morphology of the composites depends strongly on the temperature. When the isothermal crystallization temperatures increase from 180°C to 230°C, the crystal morphology of SCF/PTT composites continuously changes in the following order: nonbanded → banded → nonbanded spherulites. Discontinuous circle lines form in the film when the film thickness increases from 30 to 60 μm. Basing on the SEM observation, it is found that these circle lines are cracks formed due to the constriction difference of the different parts of the spherulites. These cracks are formed when the film is cooled from the isothermal crystallization temperature to the room temperature at a slow cooling rate; while they will disappear gradually at different temperatures in the heating process. The crack will appear/disappear first around the center of the spherulite when the film was cooled/heated. The nontwisted or slightly twisted lamellas will reorganize to form highly twisted lamellas inducing apparent banded texture of the spherulites.

Multivariate Image Texture by Multivariate Variogram for Multispectral Image Classification

Traditional image texture measure usually allows a texture description of a single band of the spectrum, characterizing the spatial variability of gray-level values within the singleband image. A problem with the approach while applied to multispectral images is that it only uses the texture information from selected bands. In this paper, we propose a new multivariate texture measure based on the multivariate variogram. The multivariate texture is computed from all bands of a multispectral image, which characterizes the multivariate spatial autocorrelation among those bands. In order to evaluate the performance of the proposed texture measure, the derived multivariate texture image is combined with the spectral data in image classification. The result is compared to classifications using spectral data alone and plus traditional texture images. A machine learning classifier based on Support Vector Machines (SVMs) is used for image classification. The experimental results demonstrate that the inclusion of multivariate texture information in multispectral image classification significantly improves the overall accuracy, with 5 to 13.5 percent of improvement, compared to the classification with spectral information alone. The results also show that when incorporated in image classification as an additional band, the multivariate texture results in high overall accuracy, which is comparable with or higher than the best results from the existing single-band and two-band texture measures, such as the variogram, cross variogram and Gray-Level Co-occurrence Matrix (GLCM) based texture. Overall, the multivariate texture provides the useful spatial information for land-cover classification, which is different from the traditional single band texture. Moreover, it avoids the band selection procedure which is prerequisite to traditional texture computation and would help to achieve high accuracy in the most classification tasks.

Model for the development of rhythmically banded wollastonite-hedenbergite skarns at the Dal’negorsk deposit, southern Russian Far East

Skarns at the Dal’negorsk boron deposit belong to the infiltration type. In their outer contact zone (bounded by limestone and consisting of wollastonite + hedenbergite), rhythmically banded textures developed, with alternating wollastonite and hedenbergite bands. The petrological study and modeling of the process that produced them led us to propose a mechanism for the genesis of such textures. They are thought to form as a consequence of a dissipative structure in the infiltrating solution and its interaction with the rock. The dissipative structure itself resulted from the instability of the equilibrium state of the skarn-solution system and the development of pervasive spatial oscillations in the redox potential of the solution. The progressive development of the banded texture was associated with a change in the dissipative structure because of the existence of feedback (mutual influence) between the structure of the solution and the texture of the rock. The rhythms generated thereby are of several orders (as follows from their thicknesses and the distances between them), which is an indication of a large-scale invariance of the developing texture. The simulation of the process involved the analysis of a system of kinetic equations, the stability of the equilibrium, and the conditions of the stability of spatial oscillations in the concentrations of major components in the solution. A necessary condition of the stability of the dissipative structure is a low velocity of fluid filtration, which should be no higher than a critical value, with the latter controlled by kinetic parameters of the system. The proposed model can be modified and adapted for rhythmically banded skarns of other composition and for banded hydrothermal mineralized veins with the aim of constraining the petrogenetic conditions and elucidating the role of banded textures as precipitators of ore and minor components of the solution.

The microstructure and rheology of carbon nanotube suspensions

This paper gives a brief overview of microstructure and rheology that have been observed for a range of carbon nanotube (CNT) suspensions. In general, untreated CNT suspensions show a much higher level of observable optical microstructure reflecting their preference to aggregate; they also show higher levels of viscoelasticity over treated CNT suspensions. An unexpected Helical Band texture for untreated CNTs is reported together with a series of parallel plate optical observations showing a broad spectrum of behaviour for different shear conditions. Both steady shear and linear viscoelastic data are presented for treated and untreated systems.

Low core loss non-oriented silicon steels

Low core loss non-oriented silicon steels are produced with high (Si+Al) content to reduce eddy current losses. However, high alloy content has detrimental effect on mechanical properties, saturation polarization and thermal conductivity. A new generation of medium and, particularly, low core loss non-oriented silicon steels was developed, with lower alloy content than the conventional grades, based on improved purity and texture. The development allowed the production of new low loss grades, with maximum core loss ( W 1.5/50) of 2.30 W/kg at 0.50 mm and 1.95 W/kg at 0.35 mm, with high permeability ( J 50 of 1.7 and 1.72 T, respectively). Texture improvement was based on hot band structure control and higher boundary mobility. Large hot band grain size and low [1 1 0]∥RD fiber fraction in the hot band texture contribute to reduce the intensity of [1 1 1]∥ND and slightly increase the intensity of [0 0 1]∥RD in the final product. Higher grain boundary mobility and/or a two-stage cold rolling process, with an intermediate annealing, increase the fraction of [0 0 1]∥RD and reduce the fraction of [1 1 1]∥ND on recrystallization and lead to favorable texture evolution on grain growth.

Concentration dependences of dielectric properties at 105 Hz and 106 Hz for aqueous solutions of hydroxypropyl cellulose

The concentration dependences of dielectric properties measured at 105 Hz and 106 Hz are reported for aqueous solutions of hydroxypropyl cellulose. Phase behaviour of the solutions was also observed with a polarizing optical microscope. For solutions with concentrations well above 40 wt %, polydomain textures, including the banded texture, were observed after a prehistory of deformation. No significant discontinuous changes in the dielectric constant, εr′, and loss factor, εr″, were found at the concentrations around the onset of the isotropic–cholesteric phase transition and in the biphasic region. In contrast, the steeper changes in εr′ and εr″ were found at the critical concentration for the fully developed cholesteric phase transition with the polydomain textures.

Shape and structure recovery of an LCP droplet under a large step strain: observation and stress calculation

Shape recovery of a droplet of liquid crystalline polymer (LCP) hydroxypropylcellulose in a matrix of poly(dimethyl siloxane) subjected to a step shear strain has been studied via optical microscopy. Just after application of a large strain, the LCP droplet shape is flat ellipsoid, and then the droplet takes cylindrical shape and band texture perpendicular to the flow direction appears. The band texture fades away before emergence of poly-domain structure. In the final process with the shape of spheroid, poly-domain structure recovers very slowly. Except for the final process, the shape change is identical with that of isotropic droplet at strains smaller than 3, when the LCP viscosity in Region II is taken as an equivalent viscosity for normalization. For a 20:80 blend, the excess relaxation modulus is calculated based on the Doi-Ohta theory, taking account of the distribution of droplet size and compared with experimental modulus data.

Computational rheooptics of liquid crystal polymers

A computational rheooptical model based on the integration of liquid crystal polymer flow equations and two well-known polarized light transmission methods is formulated and applied to the ubiquitous periodic banded textures observed in sheared lyotropic nematic polymers. The selected optical methods are the matrix-type Berreman method and the finite-difference time-domain (FDTD) direct numerical simulation method. The optical response of a single unit cell of the periodic banded texture of sheared lyotropic nematic polymers to polarized light propagation under cross-polars is analyzed and correlated to the shear-induced orientation field previously reported in Han and Rey [W.H. Han, A.D. Rey, Theory and simulation of optical banded textures of nematics polymer during shear flow, Macromolecules 28 (1995) 8401–8405]. The role of orientation gradients on the optical response is elucidated and shown to be source of lack of accuracy of the Berreman matrix method. The findings provide robust guidelines on the applicability and accuracy of matrix and direct numerical simulation optical methods. Computational rheooptics of liquid crystal polymers based on the FDTD method is an additional tool to understand flow-induced texture formation when used in the direct forward mode, and in quantitative assessments of rheological material properties when used in backward mode.

Helical Morphologies of Thermotropic Liquid-Crystalline Chiral Schiff-Based Rod−Coil Amphiphiles

A series of Schiff-based rod−coil molecules possessing thermotropic liquid-crystalline (LC) character have been prepared whereas a sugar-based moiety was introduced to the chain end of the molecules so as to create chiral amphiphiles for self-assembly. The self-assembly of the chiral Schiff-based rod−coil amphiphiles gave rise to a variety of specific LC textures. A banded morphology under polarized light microscopy (PLM) can be observed; the appearance of the banded texture is strongly dependent upon the length of hydrophobic tail that determines the twisting power of self-assembled hierarchical superstructures with helical sense. As a result, the banded spherulites are identified as quaternary helical morphology with a collection of the tertiary chiral structures (i.e., helical twists) so as to give regular extinction in PLM attributed to zero-birefringence effect. Consistent with the observation of helical morphologies, the occurrence of chiral smectic C (SmC*) phase can only be found in samples with enough alkoxyl chain length, suggesting the existence of strong correlation for morphological evolution from molecular level to macroscopic object with the formation of SmC*. A hypothetic model about the bilayer structure within the SmC* structure is thus given to elucidate the morphological evolution. Consequently, the self-assembly of the chiral amphiphiles with thermotropic LC character represents the mechanism for the chirality transfer in different length scales.

New cellulose derivatives composites for electro-optical sensors

In this work we used hydroxypropylcellulose (HPC) and acetoxypropylcellulose (APC) to produce free standing solid films (∼60 μm) for electro-optical devices. Cellulose derivatives films were prepared from crosslinked both HPC and APC isotropic and liquid crystalline solutions without and with a low molecular weight nematic liquid crystal mixture (LC) E7. Films prepared from anisotropic solutions presented a band texture and E7 droplets of micron and submicron size were found to coexist with the band texture in the films prepared with E7. The optical cells were composed by the cellulose derivatives films covered on both free surfaces by a layer of the LC E7 and placed between two transparent conducting substrates. All the electro-optical cells prepared showed switching times in the range of some milliseconds to hundreds of milliseconds. The on-voltage ( V on) is lowered for cells prepared with the ester derivative film obtained from isotropic solutions. The maximum transmission values show a clearly tendency to decrease for the cellulosic matrix prepared from anisotropic solutions with and without nematic liquid crystal droplets.

Comparison of Hot Rolled Textures in Different Grades of High Formable Steels

During hot rolling of steels phase transformation takes place. Hot band texture and hot band grain size largely influence the texture formation of cold rolled and annealed steels. Generally, a strong crystallographic relationship exists between the parent austenite phase and the product ferrite phase. The present investigation incorporates a comparative study of hot band texture formation in austenitic zone in extra deep drawing (EDD), interstitial free (IF) and interstitial free‐ high strength (IF‐HS) steels. The intensities of hot band texture in IF‐HS steel [f(g) = 19.6] were found to be much stronger in comparison to EDD [f(g) = 3.9] and IF [f(g) = 1.4] steels.

Simulation of the deformation texture of a 17%Cr ferritic stainless steel using the texture component crystal plasticity finite element method considering texture gradients

Abstract We use a texture component crystal plasticity finite element method for the simulation of plane strain compression (maximum thickness reduction 95%) of a ferritic stainless steel (X6Cr17, AISI 430, 1.4016). The method incorporates the graded hot band texture of the starting material and predicts the development of the orientation distribution during forming in the surface and in the center layer considering 24 slip systems ({1 1 0}〈1 1 1〉, {1 1 2}〈1 1 1〉). The results are compared to experiments.

Strain-induced matrix and droplets anisotropic deformation in liquid crystalline cellulose dispersed liquid crystal films

The present work deals with the preparation of new liquid crystalline cellulose dispersed liquid crystal films (100 μm) using a shearing casting technique. The matrix of the films presents the so-called band texture perpendicular to the shear direction. The nematic low molecular weight liquid crystal is encapsulated in micron and submicron size ellipsoids. The ratio between the lengths of the main axis and the short axis is around 1.23. The main axis is oriented, on average, 28° away from the shear direction. The evolution of the band texture and of the ellipsoidal liquid crystal droplets is investigated by polarizing optical microscopy and light scattering techniques as a function of the strain imposed along and perpendicular to the shear direction. Stretch along shear with strain equal to 0.8 seems to have no effect on the banded structure of the matrix, while the nematic liquid crystal ellipsoids slightly orient the main axis to the stress direction and their shape anisotropy increases by a factor of 2. Deformation in the direction transverse to the shear direction induces a deep change of the polymeric matrix and, at the end, a fibrillar structure is found. The nematic ellipsoids rotate their main axis and align along the stretch direction. Their shape anisotropy evolves from a value of 1.23 to 1 for intermediate deformations with strain equal to 0.5, to a final value of 5 with strain equal to 0.8, in the perpendicular direction.

Tunable topographical cellulose matrices for electro-optical liquid crystal cells

AbstractIn this work we have used acetoxypropylcellulose (APC) to produce free standing solid films (∼60 μm) that were used for assembling electro-optical devices. Thin films were obtained from concentrated lyotropic solutions of cellulose derivatives. Induced by the cast and shearing preparation conditions wrinkles and band textures can be observed in their free-surface plane. In order to eliminate and control these textures we used a process similar to that introducted in literature [1] which consists of storing the films in the same solvent-vapour atmosphere as the solution system. Lyotropic APC liquid crystalline solutions in dymethylacetamide (DMA) with crosslinker were prepared, thin films were obtained by using a shear/casting technique and stored in the solvent-vapour atmosphere until a planar structure was achieved. The dried crosslinked films were analyzed by optical polarised microscopy (POM) and scanning electron microscopy (SEM). The films with different topographies were used to produce optical cells composed by the cellulose derivative film covered on both free surfaces by a layer of the nematic liquid crystal E7 and placed between two transparent conducting substrates. The electro-optical properties of these cells were obtained.

Anisotropic cellulose‐derived matrix for dispersed liquid crystals

New cellulose‐derived dispersed liquid crystal free‐standing thin films were prepared by a shear‐casting technique from anisotropic and isotropic solutions of thermotropic (acetoxypropyl)cellulose in N,N‐dimethylacetamide with different amounts of the nematic E7. For films prepared from anisotropic solutions, dispersed nematic E7 droplets of micron and submicron size were found to coexist, with the band texture characteristic of polymer liquid crystals after shearing. Mechanical properties including Young's modulus and stress–strain curves were determined along and perpendicular to the shear direction, and revealed the anisotropic behaviour of films prepared from lyotropic solutions. The nematic E7 component appears to promote chain mobility and rearrangement of the polymer matrix and to modify the viscoelastic properties of the matrix.

Effect of the Elastic Constant Anisotropy on Disclination Interaction in the Nematic Polymers

In this work, disclination interaction behavior in relation to Frank elastic constant anisotropy in nematics has been studied. A large number of (+(1/2), -(1/2)) disclination pairs are revealed by spontaneous band texture in a semiflexible copolyester. The pairs show no preferential relative orientation, with the intervening fields showing intermediate patterns. A two-dimensional tensor lattice model considering unequal elastic constants is applied to simulate the interaction behavior and patterns of disclination pairs in the presence of elastic anisotropy. Scaling laws for disclination density rho(t) as a function of time step t with different elastic anisotropy are obtained as t(-nu). The value of the exponent nu decreases as elastic anisotropy is increased. Obviously, elastic anisotropy slows the texture coarsening. The simulations also show that angular forces arise in the presence of elastic anisotropy and change the patterns of pairs during the texture coarsening. When disclination density is considerably decreased, some +(1/2) disclinations start to rotate to the energetically favored patterns depending on the sign of the elastic anisotropy. As a result of the disclination rotation, the distribution of patterns of pairs continues to change during the annihilation. However, disclination pairs are influenced not only by elastic anisotropy but also by disclination interaction during the whole annihilation. Therefore, in a real system, the dependence of pairs on elastic anisotropy is not as strong as the theoretical prediction for an isolated pair, and the full pattern range of disclination pairs can be observed.