Optical microscopy, polarized

Liquid crystal materials may exhibit birefringence (discussed in Section 2.5), so polarized optical microscopy is an ideal technique for visualization of liquid crystal textures. Samples are prepared as a thin film ( 2-20 pm thick) between glass plates. By observing the interesting defect textures that may form in each phase, it is often possible to make accurate phase identifications by microscopy alone, even though the microscope is unable to resolve the actual molecular packing structure. 

In this figure, two different views of the same nematic defects are presented. In both images, the liquid crystal is shown illuminated between crossed polarizers, but the right-hand image has been rotated by 45° with 

FIGURE 2.22 Two different polarized optical microscopic images of the same brush defect in the nematic phase taken at two different arbitrary angles 45° apart. Notice how the dark areas are different in the two images as different areas of the sample become aligned with the polarizer direction. 

Finally, after passing through the analyzer (P2), aligned in the x direction, the two transmitted wave components will have amplitudes equal to 

FIGURE 2.23 Schematic showing the operation of the polarizing optical microscope. Two polarizers on either side of the sample are crossed so differences in birefringence in the sample may be observed. 

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In general, X-ray data are used in conjunction with other techniques to obtain as full a picture as possible. For liquid-crystalline materials, differential scanning calorimetry (DSC) and polarizing optical microscopy (POM) are conventionally used. 

As indicated above in chiral mesophases, the introduction of a functional group in mesogenic stmctures offers the opportunity to achieve functional LCs. With this aim, mesomorphic crown-ether-isocyanide-gold(I) complexes (26) have been prepared recently [38]. The derivatives with one alkoxy chain show monotropic SmC mesophases at or close to room temperature. In contrast, the complexes with three alkoxy chains behave as monotropic (n = 4) or enantiotropic (n > 4) LCs. The structure of the mesophases could not be fully eluddated because X-ray diffraction studies in the mesophase were unsuccessful and mesophase characterization was made only on the basis of polarized optical microscopy. These complexes are luminescent not only in the solid state and in solution, but also in the mesophase and in the isotropic liquid state at moderate temperatures. The emission spectra of 26a with n=12 were... 

Preliminary room temperature x-ray data of 0.65 Me4C00-PECH indicates that the sample presents a highly ordered smectic mesophase which was not yet completely assigned. The textures seen by polarized optical microscopy are also typical of smectic phases. Due to the very high molecular weights involved, textures specific to mesophase in thermodynamic equilibrium could not be developed within a reasonable amount of time by annealing. 

Mesomorphic dendrimers containing electroactive units have potential for construction of dendrimer based molecular switches. Deschenaux et al. reported [154] the synthesis and liquid-crystalline properties of a novel dendrimer containing six mesomorphic ferrocene units. Apart from exhibiting a broad enantiotropic smectic A phase as determined by polarized optical microscopy, DSC, and XRD studies, thermogravimetry revealed the excellent thermal stability of the macromolecule. 

In the case of extended chain crystals, we showed that a single crystal is easily formed even for Mn higher than 105. An ECSC shows a cigar-like and tapered shape morphology, observed by polarizing optical microscopy [22] and by transmission electron microscopy [48]. 

POM Polarized optical microscopy PPDX Poly(p-dioxanone)... 

The melt mixed 80/20 PS/iPP blend displays a set of exotherms, where the amount of the iPP component that was heterogeneously nucleated is substantially reduced as indicated by the decrease of the crystallization enthalpy in the temperature region where the iPP crystallizes in bulk, i.e., at 109-111 °C (exotherm labeled A). This effect is due to the confinement of iPP into a large number of droplets. If the number of droplets of iPP as a dispersed phase is greater than the number of heterogeneities present in the system, fractionated crystallization occurs. The number of droplets for this composition is known (by scanning electron microscopy observations) to be of the order of 1011 particles cm-3 and polarized optical microscopy (POM) experiments have shown that this iPP contains approximately 9 x 106 heterogeneities cm-3. In fact, it can be seen in Fig. 1 that the fractionated crystallization of the iPP compon-... 

The fiber fragment length can be measured using a conventional optical microscope for transparent matrix composites, notably those containing thermoset polymer matrices. The photoelastic technique along with polarized optical microscopy allows the spatial distribution of stresses to be evaluated in the matrix around the fiber and near its broken ends. 

Oligoester Diols. The physical properties of LC oligoester diols la-lg measured by GPC, VPO, DSC, and polarizing optical microscopy are summarized in Table I. 

With respect to the higher temperature transition at 445 °C, there are two conflicting views of this transition, namely that the phase above 445 °C is a smectic C and the other that it is nematic. Based on high temperature X-ray diffraction studies, Yoon et al. have concluded that it is a smectic C (see Fig. 4) [28], Thus, in Fig. 4, the disappearance of the 211 peak indicates that the nematic E structure is converting to a nematic C. In our work, using polarizing optical microscopy, we have observed a nematic texture for high molar mass specimens heated rapidly to 480 °C, sheared, and then quenched. In the case of a... 

In this paper we describe two types of observations on egg-yolk lecithin. We present the results of our study of homeotropically oriented samples of La phases by polarizing optical microscopy. This study provides evidence, amid apparently nonsimilar aspects, of the existence of an elementary typical object which we have interpreted as a dislocation. We also studied thin samples of stained lecithin in the high vacuum of the electron microscope. In addition to the defects that are typical of this type of sample, we observed the same elementary object as in La lecithin. 

The mesophase of 105 could not be clearly identified due to missing X-ray experiments but it was considered to be a columnar phase as deduced from polarizing optical microscopy. It was found that complexation with LiC104 and NaC104 leads to a decrease of the melting and clearing point but increasing the... 

A cholesteric, or chiral nematic (N ) phase. This is a positionally disordered fluid in which the constituent molecules align on average their axes along a common direction called the nematic director. Being the DNA helices chiral, the orientational order develops an additional macro-helical superstructure with the twist axis perpendicular to the local director. The phase thus consists of local nematic layers continuously twisted with respect to each other, with periodicity p/2 (where p is the cholesteric pitch see Fig. 8a) [27,28]. For 150-bp helices, the N phase appears at a concentration around 150 mg/mL in 100 mM monovalent salt conditions. This LC phase is easily observed in polarized optical microscopy. Since the N pitch extends to tens of micrometers (that is, across... 

Polarization, and NLO properties, 12, 102 Polarized optical microscopy, metallomesogen mesophase characterization, 12, 208 Polar monomers, polymerization, 1, 147 Polar polyolefins, co-polymerizations, 11, 723 Polyacetylenes... 

While FTIR images are similar to those that can be generated with polarized optical microscopy, the utility of fast FTIR imaging to the study of semicrystalline systems becomes apparent in the examination of blend systems. 

One might expect the nodule diameter of pure LDPE to be the same as that in the amorphous rubber/LDPE blend. This could result if the same proportion of LDPE nucleated the crystals and if no amorphous EPDM lay inside the LDPE crystallites. However, the concentration of crystallites would be lower in the blend. It is impossible for us to measure the concentration of crystallites in this blend. The resolution is inadequate and the etching depth is not accurately known. We will have to look at blends containing less LDPE to see if the crystallite concentration decreases. No spherulites are seen in these blends by polarized optical microscopy. However, these nodules are too small for optical resolution, and may indeed be spherulites or aggregates of lamellae. 

DSC differential scanning calorimetry SEC size exclusion chromatography POM polarized optical microscopy... 

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