Polarization contrast microscopy

Notes E = excellent G = good F = fair SALS, small angle light scattering PCM, polarized contrast microscopy TOA, thermal oxidative analysis. Other abbreviations are listed in Section 2.12. 

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... 

The use of a single polar is compatible with phase contrast microscopy. Crossed polars produce a dark field in which fine fibers will not be seen. If a compensator such as a first order red plate is also used, most of the fine fibers will be seen provided the light source (31) is sufficiently intense. 

In phase contrast microscopy when particles are viewed in brightfield, i.e., without the use of crossed polars, if particles have an n less than n of the medium, the particles appear very white unless the particles have a strong absorbance color. If n of the particles is close to n of the medium, the particles will appear faint blue. If n of the particles is greater than n of the medium, the particles will show sharp contrast. Edges and surface features will be easily seen. 

Smooth muscles derive their name from their appearance when viewed in polarized light microscopy in contrast to cardiac and skeletal muscles, which have striations (appearanee of parallel bands or lines), smooth muscle is unstriated. Striations result from the pattern of the myofilaments, actin and myosin, which line the myofibrils within each muscle cell. When many myofilaments align along the length of a muscle cell, light and dark regions create the striated appearance. This microscopic view of muscle reveals some hint of how muscles alter their shape to induce movement. Because muscle cells tend to be elongated, they are often called muscle fibers. Muscle cells are distinct from other cells in the body in shape, protein composition, and in the fact that they are multi-nucleated (have more than one nucleus per cell). 

In contrast to polarized optical microscopy, SALS can measure crystal structures of a smaller size (Figure 9.1c) in the range of 0.05 pm to several microns. Additionally, SALS transmission measurements can be used to obtain real-time crystallizahon kinetics since density fluctuations in the material increase with time. This technique may also be used for the detection of an induction period in crystallization. 

Figure 2.4 Phase contrast microscopy of native (a), gelatinized (c) and destwcturized potato starch (e). Polarized optical microscopy of native (b), gelatinized (d) and destructurized (0 potato starch.

In contrast to specimens that were not prepared by extrusion or injection molding but were heated and pressed without appreciable shear stress, there is no significant contrast of the LC-poor and LC-rich phases in SEM of broken samples. This is true, independent of the composition. The existence of different phases, however, can be shown with polarized light microscopy (see below). 

Optical microscopy (OM), polarized light microscopy (PLM), phase contrast microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM) are the methods normally used for identification and quantification of the trace amounts of asbestos fibers that are encountered in the environment and lung tissue. Energy-dispersive X-ray spectrometry (EDXS) is used in both SEM and TEM for chemical analysis of individual particles, while selected-area electron diffraction (SAED) pattern analysis in TEM can provide details of the cell unit of individual particles of mass down to 10 g. It helps to differentiate between antigorite and chrysotile. Secondary ion mass spectrometry, laser microprobe mass spectrometry (EMMS), electron probe X-ray microanalysis (EPXMA), and X-ray photoelectron spectroscopy (XPS) are also analytical techniques used for asbestos chemical characterization. 

Then, microscopic examinations follow optical research microscopes allow to determine the number, thickness, and color sequence of layers in paint fragments, and to recognize the textures as well as fundamental features of pigment and extender mixtures. Bright field and dark field illuminations, polarized light microscopy (incident and transmitted), particularly the differential interference contrast (DIC) procedure, and fluorescence microscopy are necessary for paint examinations (see Figure 3(A)-3(E)). 

---