Polarizing microscopy, textures

The textures in homeotropic lamellar phases of lecithin are studied in lecithin-water phases by polarizing microscopy and in dried phases by electron microscopy. In the former, we observe the La phase (the chains are liquid, the polar heads disordered)—the texture displays classical FriedeVs oily streaks, which we interpret as clusters of parallel dislocations whose core is split in two disclinations of opposite sign, with a transversal instability of the confocal domain type. In the latter case, the nature of the lamellar phase is less understood. However, the elementary defects (negative staining) are quenched from the La phase they are dislocations or Grandjean terraces, where the same transversal instability can occur. We also observed dislocations with an extended core these defects seem typical of the phase in the electron microscope. 

We studied samples of La lecithin with 16-29% water at room temperature. The samples were prepared between two microscope glass slides that were first treated with a sulfochromic solution, then carefully rinsed with distilled water and dried. They were observed by transmission polarizing microscopy. Just after deposition between the slides, the samples present a highly disordered texture which strongly diffuses light. After compression (squeezing) and/or shearing parallel to the plates, one obtains an overall homeotropic orientation that is perturbed by defects. The thickness of the samples is in the order of 20/. ... 

A dispersion of spherulitic liquid crystalline particles in brine exists between 0.8 gm/dl NaCl (Figure 2(a), first sample on the left) and 1.2 gm/dl. As the salinity is increased to about 1.4 gm/dl NaCl, the amount of liquid crystals as well as the birefringence increase, and the texture observed using PLS is intermediate between those of the spherulite (S) and lamellar (L) structures. The aqueous solution is a homogeneous lamellar phase between 1.6 and 1.8 gm/dl NaCl. The surfactant molecules form bilayers with their polar heads toward the brine. Figure 3(a) shows the lamellar structure as observed by polarized microscopy at 1.6 gm/dl salt and without any polymer. The bands represent "oily streaks" in a planar background. 

The dynamics of polymer-induced phase separation have been observed with polarized microscopy. Figures 3(b) and 3(c) show the textures when 750 ppm Xanthan gum was added to the system of 3(a). Figure 3(b) was observed one day after addition of polymer, and Figure 3(c) a week later. As expected, the polymer phase represented by the darker region has separated out to a greater extent after a week. 

Figure 4 Texture of the highly mobile, photosensitive nematic phase Np of the title compound measured by polarization microscopy (scale 1 340).

The N + I biphase finds its origin in polydispersity in chain length coupled with polydispersity in chain flexibility and is observed within a temperature range delineated by and T. Polarizing microscopy observation of the biphase in Pi (n = 10, M = 18 700) is illustrated in Figures 6.5a-c for three different conditions of thermal history [42]. It is apparent that textures and biphase width both depend on sample thermal treatment. 

Moreover, in direct correspondence between structure, energy flow, and photophysics, pure PA exhibits minimal or no fluorescence, whereas functionalized acetylenes [206,207] or phenylacetylenes [208] can be highly emissive with some derivatives exhibiting photoluminescent yields that approach unity. Liquid crystallinity is often observed with the formation of various nematic or smectic phases. These can be easily inferred through polarized microscopy and the appearance of Schlieren and related mesomorphic textures. Functionalization with chiral-branched substituents [209,210] leads to optically active polymers. 

The pleated sheet can also be observed with optical polarization microscopy [119, 133]. Fig. 15 demonstrates the origin of the various banded patterns in the polarizing microscope, which are seen on a longitudinal section of a fiber. In the dark areas the chains are aligned parallel to the analyzer or polarizer direction. Such a banded texture is often observed in films and fibers of lyotropic and thermotropic polymers. 

The optical polarizing microscopy analysis of these copolymers showed in all cases schlieren nematic textures, in contrast to the corresponding polyethers which present smectic type textures. All these copolyethers are soluble in aromatic and halogenated solvents. 

The low transition enthalpies of about 1.5 kJ/mol indicate mesophase transitions. This was confirmed by polarizing microscopy, which show,beside homeotropic domains,also focal conic textures. 

Observation by polarizing microscopy shows typical textures of the smectic A phase between and 7] for all samples. Clearing and transformation to the isotropic liquid are observed approximately 2-7 K above the melting points. The temperature interval within which the liquid crystalline phase exists, AT, is narrow, and this interval decreases linearly as the chain length of catanionics increases, according to the equation... 

TFAA-methylene chloride mixture results in the formation of similar textures that indicated the formation of an XRD-detectable nematic liquid crystal. Thus, the deformation of CBS solutions leads to the change of an LC type from cholesteric to nematic. When the deformed solutions were studied by the method of polarization microscopy, the development of striped textures was observed (fig. 4). This fact is indicative of the formation of the domain supramolecular structure (Papkov Kulichikhin, 1977, Aharoni Walsh, 1979). Since, compared to cholesteric liquid crystals, nematic liquid crystals exist at higher temperatures, the temperature-concentration region corresponding to the existence of anisotropac solutions under the mechanical field should change. 

Polarization microscopy studies revealed a striped texture of HPC and CEC solutions treated in magnetic field (fig. 7), thus suggesting formation of large supramolecular structures—domains. A similar phenomenon was reported for other polymer-solvent systems (Papkov Kuhchikhin, 1977). 

Fig. 3.13. Texture of the hexagonal (a) and lamellar phase (b) obtained using polarizing microscopy.

The identification of the Nc and Nd phases can be archived by polarization microscopy based on their different textures which are presented in Fig. 11.28 a and 11.28 b. H-NMR spectroscopic studies and orientation experiments on the nematic phases in a magnetic field are suitable for their detection, especially if SANS measurements are done on oriented samples. For these experiments the phases have to be prepared with D2O instead of H2O. This... 

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