Optical texture examined

However, further analysis of the behavior of the system in LC cells cast doubt on this interpretation. First, while intuitively attractive, the idea that relaxation of the polarization by formation of a helielectric structure of the type shown in Figure 8.20 would lower the free energy of the system is not correct. Also, in a thermodynamic helical LC phase the pitch is extremely uniform. The stripes in a cholesteric fingerprint texture are, for example, uniform in spacing, while the stripes in the B2 texture seem quite nonuniform in comparison. Finally, the helical SmAPF hypothesis predicts that the helical stripe texture should have a smaller birefringence than the uniform texture. Examination of the optics of the system show that in fact the stripe texture has the higher birefringence. 

In situ X-ray examination of crystallizing polyethylene, at high temperature and pressure, then confirmed this proposal in detail, showing that the wide-angle diffraction pattern changed abruptly with the optical texture [ 10]. That corresponding to the spherulitic texture was of the usual orthorhombic form while the new intermediate phase had two-dimensional hexagonal symmetry, with an increased cross-sectional area per chain, but without... 

Marsh et al, (60, 64) examined optical textures of cokes from carbonizations of soluble and insoluble fractions of coal-extract solutions as well as conditions of extraction. Generally, the low-molecular-weight fractions of the coal-extract solution produced cokes with larger sized optical textures than the coke from the parent coal-extract solution. The higher-molecular-weight fractions produced cokes with smaller sized optical texture. Isotropic coke was produced from material which was insoluble in benzene and tetrahydrofuran. 

Chemical Modifications to Pitch. The earlier attempts to improve the commercial value of pitch residues must have been essentially exploratory research. Sanada et al, (71) in 1973 methylated the hydroxyl groups of 3,5-dimethyl phenol formaldehyde resin and noted, on carbonization, the formation of spheres of mesophase, the original resin giving an optical texture of mosaics in resultant carbons. Mochida et al. (72) carbonized naphthalene, anthracene and pyrene with aluminium chloride, sodium and potassium and examined the structure of the resultant carbons by optical microscopy and high resolution, fringe-imaging transmission electron microscopy (TEM),... 

Sulphur, or sulphur-containing heterocyclics induce the formation of cokes of small sized optical texture (22) Mochida et al. (75) examined the carbonization behaviour, in the presence of aluminium chlorides, of diphenyl sulphide, thioxanthene and thianthrene,... 

Gasification and Heat Treatment. Examination under the optical microscope showed the Spencer works and Clyde Ironworks cokes to have optical textures mainly consisting of fine- and medium-grained mosaics with some coarse flow anisotropy and isotropic inert material. Of particular interest are the fissures which develop in different types of optical texture and those occurring at the anisotropic-inert interface. SEM examination of these polished surfaces before experimentation shows all of them to be flat and featureless. 

Figure 4 shows the same area examined by SEM after heat treatment. Once again, comparison shows fissures of the same size and orientation as the optical texture (predominantly medium-grained mosaics) to have developed (Position D ). These fissures appear... 

In the series of complexes with twelve chains ((55) M = Cu, Pd, VO R = OC H2 +i, = 6, 8, 10, 12, 14), an unusual phase sequence was observed (Table 34). The copper and palladium complexes displayed enantiotropic, disordered Coh and Coin phases, identified by their optical texture, and by X-ray diffraction. Quite uniquely, the Coin phase was systematically the lower-temperature mesophase, observed below the Coh phase. For the copper complexes, a Coir phase was seen for short-chain compounds with a transition to a Colh phase for n > 10. The intermediate octyloxy derivative displayed an unusual, but reproducible, I-Coh-Colh-Colr-Colh-Colh phase sequence on cooling from the isotropic liquid, several of these transitions being weakly first order. The decyloxy analog displayed a Colh-Colh-Colh-Colh phase sequence, and the two next homologous compounds showed a single Coin phase. To have, supposedly, so many phases of apparently the same symmetry in a single material is most unusual and no explanation was offered to help understand the phenomenon. It is to be hoped that at some stage they may be subject to re-examination so that this exotic behavior may be properly understood. 

Optical microscopy, using polarized reflected light, has been recognized as a very useful tool and has played a major role in studies of carbonization mechanisms and coke quality properties. Examination of a coke polished surface under a microscope reveals the presence of certain parts without optical activity (isotropic coke) and others with optical activity (anisotropic coke). The anisotropic carbon exhibits yellow, blue, and purple areas of various sizes, <1-200 )tm, and shapes (optical texture) with an interchange of color on rotation of the specimen. 

We have described lattice spin models for the simulation of polymer-dispersed liquid crystals. The biggest advantage of Monte Carlo simulations is the possibility of investigating the system at a microscopic level, and to calculate thermodynamic properties and their specific order parameters suitable for different types of PDLC. Molecular organizations can be investigated by calculating the order parameters point by point across the droplet. Moreover, it is possible to calculate experimental observables like optical textures and, as discussed here, NMR line shapes. We have given an overview of the method and some applications to models of PDLC with radial and bipolar boundary conditions, and considered the effect of orientational and translational diffusion on the spectra. We have examined in particular under what conditions the NMR spectra of the deuterated nematic can provide reliable information on the actual boundaries present in these submicron size droplets. 

The uniaxial nematic (Ny) phase usually exhibits a schlieren texture with two and four point singularities (two and four brushes). However, the texture exhibited by complex 2, shown in Fig. 4, often consists of [S] = l/2 (two-brush) disclinations similar to that exhibited by a smectic C phase. Also, this complex showed zig-zag disclinations [24] occasionally, and since this type of disclination has been observed in N phases [25] it cannot be regarded as conclusive evidence for biaxiality. It is also possible that an entanglement of disclination lines may lead to topological rigidity, as discussed by Toulouse [26] and others [27-29]. These possibilities have not been examined experimentally. Hence optical textures that... 

A comparative study has been made by optical and electron microscopy of the anisotropic texture of several cokes from caking coals and pitches carbonized near their resolidification temperature. A simple technique made it possible to examine, by both methods, the same area of each sample and to identify the corresponding zones of the two very similar images. The anisotropy observed in polarized light appears in electron microscopy as differences in contrast resulting not from inequalities in electron absorption, but, as revealed by microdiffraction and dark Reid examinations, from diffraction phenomena depending on the general orientation of the carbon layers within each anisotropic area. 

We shall first examine the microscopic techniques which allowed us to study these transformations and to show the striking analogy between the images obtained by optical microscopy in polarized light and by electron microscopy with ultrathin sections, despite the difference of the absorption mechanisms of light and electrons. Once this analogy was established, we sought to use electron microscopy and electron microdiffraction to learn more about the texture and structure of the anisotropic areas. 

Monomeric l.c. s show in the polarizing microscope under crossed polarizers characteristic textures, owing to their optical anisotropy 51). Examining a nematic phase, which is sandwiched between untreated glass plates, typical interferences are observed, because of the variations of the optical axis with respect to the incident of light. The nematic polymers exhibit a similar bevahior. In Fig. 10a a typical picture of the texture of a polymer is shown. While for 1-l.c, s the texture can be observed immediately after preparation because of their low viscosity, in most cases the polymers samples... 

Several plagioclasc grains from annealed samples as well as shock-loaded run products were embedded in epoxy resin and polished. Observation was performed with an optical microscope using reflected and transmitted light Major and minor element compositions were determined by an electron probe microanalyzer. Shock textures were also examined in detail with a scanning electron microscope using back-scattered electron images. 

Stable carbon and oxygen isotopes of the different diagenetic carbonates were determined in 22 sandstone samples, which were selected after careful optical and cathodoluminescence examination. Samples in which contamination caused by allo-chems or mixtures of different textural types of calcite (both easily recognized by optical petrography and cathodoluminescence) were not considered for isotopic analysis. The Kiel system for calcite sample preparation was used, and calcite was reacted with anhydrous phosphoric acid at 25°C under vacuum for 2 h, the produced COj was... 

Orthoscopic examination with crossed polars is carried out first of all to determine the isotropism or the anisotropism of a sample. The polarization colors, the defects and variation in molecular orientation, and the orientation pattern or texture of liquid crystals are observed in this examination. With a heating stage the temperature of phase transition is also determined. In addition, with use of a compensator, the determination of vibration directions of the ordinary and extraordinary rays, the determination of relative retardation and birefringence are possible. In this section, the optical basics for orthoscopic observations are briefly outlined. The description of textures frequently observed for polymeric liquid crystals is given in Section 4.1.4. 

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