Polarized light microscopy fibers

Microscopy (qv) plays a key role in examining trace evidence owing to the small size of the evidence and a desire to use nondestmctive testing (qv) techniques whenever possible. Polarizing light microscopy (43,44) is a method of choice for crystalline materials. Microscopy and microchemical analysis techniques (45,46) work well on small samples, are relatively nondestmctive, and are fast. Evidence such as sod, minerals, synthetic fibers, explosive debris, foodstuff, cosmetics (qv), and the like, lend themselves to this technique as do comparison microscopy, refractive index, and density comparisons with known specimens. Other microscopic procedures involving infrared, visible, and ultraviolet spectroscopy (qv) also are used to examine many types of trace evidence. 

On the basis of this discussion, the mechanisms of mesophase carbon fiber formation are closely related to those of needle coke, the principal differences being the extent to which the deformation and relaxation mechanisms are able to act. Because delayed coking involves relatively gentle but random deformation processes by bubble percolation and the long dwell times in the coke drum afford opportunity for extensive disclination annihilation and micro-structural relaxation, the structure of needle coke can be well defined by polarized-light microscopy (2,36). 

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). 

Figure37. (a) Crystalline and right-handed helical fibersmadeofGlc-NC(12)CN-Glc (116, n= 12) observed using polarized light microscopy (at 25 C in water). Periodical structures of the fibers are denoted by arrows, (b) Polarized light micrographs of representative dehydrated and right-handed fibers from Glc-NC(12)CN-Glc (116, rt = 12), (top) photographed trough cross-polarized filters and (bottom) through plane-polarized filters. Reproduced from ref. 338 (Shimizu and Masuda, J. Am. Chem. Soc. 1997, 119,28)2) with permission of the American Chemical Society.

Polarized light microscopy of compression wood of spruce (Picea abies), image of helical cellulose fibers in adjacent cell walls (courtesy of Dr I. Burgert, Max Planck Institute of Colloids and Interfaces, Potsdam/Golm, Germany). 

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. 

Figure 5.24 Schematic representation of carbon fiber structures obtained from Courtelle precursor, (a) Isotropic center—with an outside skin of oriented crystalline material, (b) Double cross— with the outside showing a different orientation to that of the center, (c) Single cross—where the complete fiber shows one type of preferred orientation. Source Reprinted from Knibbs RH, The use of polarized light microscopy in examining the structure of carbon fibres, J Microscopy, 94(3), 273-281, 1971.

Nyo et examined PAN based Hitco carbon fibers using polarized light microscopy and found that high modulus fibers have a dual structure, with an onion skin like layer on the surface and a radial in the core (Figure 12.7). 

Presence of TCL changes the properties of crystalline matrix. Transcrystallization of isotactic polypropylene in the presence of different fibers has been thoroughly analyzed. Gray as the first one provided detailed description of isotactic polypropylene behavior in the presence of wood fibers using polarized light microscopy. He observed that when melted polymer is cooled down, it crystallizes in spherulite forms in nonisothermal and isothermal conditions, creating additionally a TCL. 

Observations of polypropylene crystallization by polarized light microscopy helped to understand phenomena on interphase of polymer-filler. When analyzing the influence of the filler, many researchers noted transciystallization of the polypropylene as a result of high enough nucleation density rai the filler s surface and also in the presence polypropylene fibers. The addition of both mineral substances and natural composites containing lignocellulosic material can induce formation of TCL. 

Waddon et al [315] have extensively studied the crystal texture of PEEK, PEK and PPS, including melt grown spherulites using polarized light microscopy. They formed thin films by heating the polymer and the fibers on microscope slides and pressing them or smearing between the slides and coverslips. Polymers were chosen... 

Polarized light microscopy has shown micrometer-sized domains in the thermotropic LCPs aligned along the fiber axis. The meander of the domains is consistent with their polarization colors (Fig. 5.87, color section). The domains... 

The collagen fiber alignment angles, obtained from polarized light microscopy (PLM) and diffusion-tensor imaging (DTI), were statistically compared in five samples of the bovine articular cartilage from five different... 

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