Banded Texture Research Articles

{111}熱延集合組織を有するIF鋼からの強い {111} 冷延集合組織形成機構

{111}熱延集合組織を有するIF鋼からの強い {111} 冷延集合組織形成機構

Recent advances in theoretical liquid crystal rheology

Recent significant advances in theoretical liquid crystalline rheology are presented. Dynamic simulations are performed using a complete theory which include the three major effects of liquid crystalline materials: (1) short range order elasticity, (2) long range order elasticity, and (3) viscous flow effects. The results and discussions include rectilinear simple shear flow, complex non-linear phenomena such as defect texture generation and coarsening processes under quiescent and shear conditions, and pattern formation such as banded texture during and after cessation of flow. The complete theory predicts four in-plane (1-D orientation) flow modes and five out-of-plane (2-D orientation) flow modes in one-dimensional shear flow, depending on the magnitudes of R (ratio of short to long range order elasticity) and Er (Ericksen number: ratio of viscous to elastic force). The multistability of these flow modes is clearly explained in terms of degrees of freedoms in the nematic orientation. The number of degrees of freedom increases with increasing the spatial dimension of the system, and thus more complex orientation patterns arise in the higher dimension. Well-known defect structures arise and coarsen during simulations of the isotropic to nematic phase transition. The effect of shear flow on the defect generation process is to suppress the defect nucleation, and the simulations suggest a method of how to create defect-free nematic samples. The banded textures during and after cessation of flow are also captured by the complete theory.

Solvent composition dependence of band morphology in sheared lyotropic ethylcellulose liquid crystals

The width, regularity, and relaxation behaviour of the banded texture varies with the solvent of lyotropic ethylcellulose liquid crystals. The bands in dichloroacetic acid are wider, more stable and more regular than those in glacial acetic acid or acrylic acid. The band width decreases with increasing concentration of the liquid crystalline solutions. The phenomena are tentatively explained with a contraction mechanism. The extended chain conformation favours relatively wide, regular, and stable bands.

Banded Texture Induced by an Electric Field in Polymeric Liquid Crystalline Solution

Using polarizing microscopy. we investigated the textural transformation and development of banded texture for cholesteric (nematic) liquid-crystalline solutions of poly(γ-benzyl glutamate) (PBG)s in an in-plane electric field. The threshold value for producing the uniform director orientation depends on cell thickness. d, and is inversely proportional to d 1 2 .In the solution aligned uniaxially by a dc field, the transient banded texture appears perpendicular to the field soon after inversion of the field direction. By using video-recording technique, detailed analysis of the texture can be performed and the following results are obtained: the appearance of banded texture is related to rotation of the director during realignment and two peaks of the optical intensity transmitted through the sample between crossed polarizers appear until the reorientation is completed: the band spacing remains constant during realignment and depends on the applied field strength: being a decreasing function of field strength. The effect of cholesteric twist on the kinetics of director rotation is studied for solutions of poly(γ-benzyl-L-glutamate (PBLG), poly(γ-benzyl-D-glutamate (PBDG) and racemic mixtures. A cholesteric twist was noted to affect kinetics of director rotation.

Arcuate band texture in a dark inclusion from the Vigarano CV3 chondrite: Possible evidence for early sedimentary processes

Abstract— A dark inclusion in the Vigarano CV3 carbonaceous chondrite consists almost exclusively of small (<5 μm in diameter) grains of Fe‐rich olivine and is devoid of chondrules, Ca‐Al‐rich inclusions (CAIs) and their pseudomorphs. In backscattered electron images, this dark inclusion shows an unusual texture comprising a network of arcuate bands. Two or more bands occur roughly parallel, forming a set of succesive parallel bands, some crosscutting one another. The bands contain slightly higher amounts of relatively small (<1 μm) olivine grains and so are more densely packed than other areas. The olivine grains in the bands are slightly more Fe‐rich than those in other areas. The bands commonly show gradation on the concave side due to a decrease in the abundance of the small Fe‐rich olivine grains. Texturally, the arcuate bands closely resemble “dish structures” that are commonly observed in siltstones and sandstones on Earth. Dish structures are characterized by thin, dark‐colored, subhorizontal to concave‐upward laminations that are rich in relatively fine‐grained material. On Earth, dish structures form during compaction and dewatering of unconsolidated fine‐grained sediments; they are one of the characteristic sedimentary structures formed through fluidization of fine grains. The dark inclusion in Vigarano, therefore, provides the first evidence that sedimentary processes due to water migration may have taken place within planetesimals and further suggests that fluidization may have played a significant role in the formation of the carbonaceous chondrites.

Textures during recoil of anisotropic hydroxypropylcellulose solutions

The recoil of anisotropic hydroxypropylcellulose solutions was studied by optical microscopy and light scattering. Different stresses were applied before stopping the flow and observing the recoil. At low stress levels, the scaling of the recoverable strain versus scaled relaxation time applies. A change of texture is noticeable only after most of the strain has been recovered. At a high stress level, a band texture appears during recoil. The appearance of this band texture stops the recovery process until the band texture disappears, and the recovery process then continues. The presence of a band texture during recoil is shown to promote a larger recoil.

Preliminary communication - The synthesis and thermotropic liquid crystalline behaviour of novel main chain poly(aryl ether ketone)s containing a lateral phenyl group

Novel main chain poly(aryl ether ketone)s containing a lateral phenyl group were synthesized by nucleophilic substitution reactions of 4,4-biphenol and phenylhydroquinone with either 4,4-difluorobenzophenone or 1,4-bis(4-fluorobenzoyl)benzene and their thermotropic liquid crystalline properties were characterized by a variety of experimental techniques. Thermotropic liquid crystalline behaviour was observed in the copolymers containing 50 and 70 mol% biphenol. Melting (Tm) and isotropization (Ti) transitions both appeared on the DSC thermograms. A banded texture was formed after shearing the sample in the liquid crystalline nematic state. As expected, each of the copolymers had a relatively lower melting transition than the biphenol-based homopoly(aryl ether ketone)s because of the copolymerization effect of the crystal-disrupting monomer phenylhydroquinone.

Texture of Shear Bands in Al-Mg 3% (AA5182) Measured by BKD

Polycrystalline Al-Mg-3% specimens were deformed by biaxial compression or tensile expansion Preferred orientations were determined in shear bands and in the abutting matrix by Automated Crystal Orientation Measurement (ACOM) from backscatter Kikuchi patterns in the SEM. From x-ray pole figure and individual grain orientation data, respectively, the ODF of global texture as well as local texture of shear hands and the neighboring matrix have been calculated with the series expansion method for triclinic sample symmetry. The conclusion, by comparing local with global textures, is drawn that shear band texture is very similar to the usual deformation texture of aluminum provided that the reference system is rotated about the transverse direction by the angle of shear band incliniation.

Recrystallization and Related Phenomena. Texture Evolution during Cold Rolling and Recrystallisation of IF Steel with a Strong {111} Hot Band Texture.

For a new industrially processed, hot rolled Ti+Nb IF steel, finished in the ferrite region and subsequently annealed, the texture development during cold rolling and annealing is investigated. The strong hot band texture is of the {554} <225> peak type. During cold rolling, the absolute maximum shifts from {554} <225> to {111} <112> along the ε-fibre and the local maximum along the α-fibre shifts from {111} <110> to {223} <110>. During recrystallisation, the weaker α+stronger γ-fibre cold rolling texture is transformed to a very strong γ-fibre annealing texture. Hereby, {111} <110> and, to a much lesser extent, {554} <225> develop at the expense of {111} <112>. Orientation Imaging Microscopy (OIM) reveals that γ-fibre grains nucleate and grow in the beginning of recrystallisation by consuming γ-fibre components of the deformed matrix. Already after 23% recrystallisation, the texture of the recrystallised grains is very similar to the one obtained after full recrystallisation. Moreover, {111} <110> grains are found to be larger and more numerous than {554} <225> grains. The former therefore have an advantage over the latter for consuming the partial α-fibre grains during the final stage of recrystallisation and for further development during grain growth. As a result, a very strong {111} <110> peak type annealing texture is obtained in the present material, resulting in extremely good deep drawability.

Viscosity of a liquid crystalline polymer solution with a polydomain or a band texture

Viscosity of a liquid crystalline polymer solution with a polydomain or a band texture

Rheology and Shear Orientation of a Nematic Liquid Crystalline Side-Group Polymer with Laterally Attached Mesogenic Units

The shear orientation of a nematic side-group liquid crystalline polymer (SG-LCP) with side-on fixed mesogenic units was investigated by means of rheo-birefringence and rheo-small angle light scattering. Rheological properties of the polymer depend on molecular weight. Macroscopically aligned samples were obtained in creep experiments, but the orientation was destroyed by oscillatory shear flow. The shear modulus of a low molar mass sample in the nematic and isotropic phase superposed to a common master curve. The low-frequency modulus of a high molar mass sample, however, decreased at the phase transition, and time−temperature superposition was not possible. Preshearing led to a further decrease of the modulus. Rheo-birefringence measurements revealed a clear influence of molar mass on both the final value and the orientation state after cessation of shear. Rheo-small angle light scattering also showed a strong influence of molecular weight. In polarizing microscopy, a banded texture was observed with a ...

Viscosity of a liquid crystalline polymer solution with a polydomain or a band texture

The viscosity of a main-chain liquid crystalline polymer (anisotropic aqueous solution of hydroxypropylcellulose) is measured in the case where the liquid crystalline polymer presents a band texture and is compared to the case of a polydomain texture.

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.

Banded Texture Induced by an Electric Field in Lyotropic Liquid Crystals

Using polarization microscopy, the formation of transient banded textures in a liquid crystalline solution of poly(γ-benzyl L-glutamate), PBLG, that had applied in-plane DC and AC electric fields was investigated. Striped bands perpendicular to the direction of the electric field were observed under an applied electric field. The images depended on time and were recorded by video camera and then analyzed. The dynamics of director-reorientation was followed by the measurement of the optical transmittance of a sample between crossed polarizers. A reproducible optical response to a low frequency square wave was observed. The dependencies of the band spacing and the reorientation rate of director on the field strength were quantitatively investigated.

The synthesis and thermotropic liquid crystalline behavior of the novel poly(aryl ether ketone)s containing chloro-side group

The novel poly(aryl ether ketone)s containing chloro-side group were synthesized by nucleophilic substitution reactions of 4,4′-biphenol and chlorohydroquinone with either 4,4′-difluorobenzophenone(BP/CH/DF) or 1,4-bis(p-fluorobenzoyl)benzene (BP/CH/BF) and their thermotropic liquid crystalline properties were characterized by a variety of experimental techniques. The thermotropic liquid crystalline behavior was observed in the copolymers containing 50 and 70% biphenol. Melting transition (Tm) and isotropization transition (Ti) both appeared in the DSC thermograms. A banded texture was formed after shearing the sample in the liquid crystalline state. The novel poly(aryl ether ketone)s had relatively higher glass transition temperature (Tg) in the range of 168 ∼ 200 °C and lower melting temperature (Tm) in the range of 290 ∼ 340 °C. The thermal stability (Td) was in the range of 430 ∼ 490 °C.

High-performance aromatic polyimide fibers. 6. Structure and morphology changes in compressed BPDA-DMB fibers

A high-performance aromatic polyimide fiber has been spun from a high molecular weight polyimide synthesized from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 2,2′-dimethyl-4,4′-diaminobiphenyl (DMB). The fiber exhibits not only excellent tensile properties and high temperature resistance but also a high compressive strength of 655 MPa. Morphological observations of BPDA-DMB fibers indicate that the fiber shows a skin-core structure and microfibrillar textures. A banded texture can also be found with a spacing of about 2μm, which may be introduced by the liquid crystalline behavior that appears during processing. Compressed BPDADMB fibers form kink and microkink bands over different size scales. The detailed formation mechanism of these banded textures is discussed. The structure parameter changes during compression-including crystal unit cell parameters, apparent crystallinity, crystal and overall orientation, and apparent crystallite sizes-are monitored. It is found that after restretching, the crystal and overall orientation is almost fully recovered while the apparent crystallinity is not recoverable. The structural changes during compression are critically associated with the loss of macroscopic mechanical property in the fibers.

Occurrence of Both Sinusoidal and Zigzag Supermolecular Structures Associated with Band Textures in a Liquid Crystalline Polymer

Occurrence of Both Sinusoidal and Zigzag Supermolecular Structures Associated with Band Textures in a Liquid Crystalline Polymer

Occurrence of Both Sinusoidal and Zigzag Supermolecular Structures Associated with Band Textures in a Liquid Crystalline Polymer

Occurrence of Both Sinusoidal and Zigzag Supermolecular Structures Associated with Band Textures in a Liquid Crystalline Polymer

γ‐Ray polymerization of lyotropic solutions of cellulose derivatives under retention of the macroscopic order

AbstractTwo new lyotropic solutions of cellulose derivatives are reported which can be polymerized upon γ‐irradiation. The first solution consists of hydroxypropylcellulose (HPC) in N,N‐dimethylacrylamide (DMAcr) and the second of 2‐(acryloyloxy)propylcellulose (APC; degree of substitution (DS) = 0.18) in water. Both solutions were characterized using refractive index measurements, polarizing microscopy and diffuse reflection spectroscopy. For solutions of HPC in DMAcr, it was demonstrated that they exhibit anisotropic phase behaviour at concentrations higher than 45 wt.‐% within a limited temperature range. Highly concentrated solutions of about 70 wt.‐% also showed cholesteric phase behaviour with iridescent colours. Upon γ‐irradiation, the solvent DMAcr rapidly polymerized. A conversion to 90% of polymer was reached at a dose of 5 kGy. Molecular composites of HPC in polymerized DMAcr were obtained in which the macroscopic order was preserved. Shear‐deformed samples were still birefringent and exhibited band textures, when viewed between crossed polarizers, and light reflection of the cholesteric samples still occurred at the same wavelength as before irradiation. The polymerized samples showed an extended temperature stability, the anisotropy being stable up to approximately 150°C. The second solution of APC in water also exhibits cholesteric phase behaviour at a concentration of 61.5 wt.‐%. Upon γ‐irradiation, the polymer chains undergo rapid cross‐linking via the reactive acrylate groups and form a network in which the cholesteric order is preserved. The cross‐linked APC films are swellable in water and retain their anisotropic order when the concentration of the solution is varied between 40 and 100 wt.‐% of APC. The materials properties of the two systems after polymerization are compared.

Texture and microstructure evolution during cold rolling of a strip cast and of a hot rolled austenitic stainless steel

The microstructure and texture evolution of a strip cast and of a hot rolled austenitic stainless steel (18% Cr, 8.5% Ni) during cold rolling was studied (maximum thickness reductionΔd/d 0= 80%). The microstructure of the hot band was homogeneous through the sheet thickness, except that in the centre layer a small volume fraction of martensite appeared. The hot band texture revealed a through-thickness gradient which was discussed in terms of the shear distribution during hot rolling. The microstructure of the cast strip showed globular grains with martensite in the centre layer and blocks of austenitic dendrites in the other layers. The formation of martensite was attributed to the deformation of the solidified films in the rolling gap. The strip cast sample revealed a weak texture fibre close to {001}〈 uvw〉 which was interpreted in terms of growth selection during solidification. During cold rolling in both types of samples the volume fraction of martensite increased up to ≈ 50 vol.% (80% reduction). The cold rolling texture of the austenite was in both cases characterized by {011}〈211〉 and {011}〈100〉. The cold rolling texture of the hot band was stronger than that of the strip cast sample which was attributed to the influence of the starting texture and of the grain size. The cold rolling texture of the austenite was simulated by means of a Taylor type model considering grain interaction and the so-called card glide mechanism. The martensite texture was characterized by {211}〈011〉 and {111}〈211〉. The former component was interpreted in terms of the relaxation of shear constraints. The latter was attributed to selective phase transformation of {011}〈211〉 (austenite) to {332}〈113〉 (martensite) which then rotated towards {111}〈112〉. The rolling textures of the martensite were simulated using a Sachs type deformation model.