Polarized light microscopy applied

Starch can be destructurized using extrusion technologies in specific conditions. Sufficient work, heat and time have to be applied to a cereal-based starch product in the presence of plasticizers to destructurize it. The best plasticizer for starch is water in quantities lower than 45%. Other plasticizers are glycols such as glycerol and sorbitol. Whereas thermoplastic starch can contain a certain amount of granular residue and a few Maltese crosses can be detected in polarized light microscopy, destructurized starch is substantially free from those features. 

W. C. McCrone, L. B. McCrone, and J. G. Delly, Applied Polarized Light Microscopy, Ann Arbor Science Publishers, Ann Arbor, Mich., 1978. 

A wide range of microscopy techniques are applied to the characterization of engineering resins and plastics. For example, crystalline polymers are viewed by polarized light microscopy to reveal the size and distribution of spherulites and the nature of the local orientation. Surface details, such as wear and abrasion are best viewed by SEM. For example, Vaziri et al. 

Soft crystal phases are more difficult to identify only by polarized light microscopy, because changes in the aspect of optical textures are very few. To determine the transitions between different phases of a soft crystal, the differential scanning calorimetry technique should be applied, while the structure, and the soft crystal type can be identified by X-ray diffraction. 

In a nematic liquid the director field is not uniform unless an external field of electric, magnetic or mechanical nature is applied. The director may vary in a smooth continuous way around certain points called disclinations, or more abruptly as in domain walls. Characteristic of the nematic structure are the so-called schlieren textures which are readily observed by polarized light microscopy (Fig. 6.23). The dark bands meet at certain points, the disclinations. It should be noted that a dark region indicates that the local molecular director of the optically anisotropic region is parallel to the polarizer or to the analyser, or that the region is optically isotropic. 

In the study of spherulites formed in poly(ester urethane) multiblock copolymer [51], FTIR imaging was used to reveal valuable information about both the orientation of the polymer chain and the composition of the spherulites. This information was not available from the measurements obtained from atomic force microscopy or polarized light microscopy. A separate study has also demonstrated that linear polarized FTIR imaging is a powerful tool for the investigation of the crystalline and amorphous structures and chain orientation of spherulites of PHB and isotactic poly(propylene oxide) [52]. Recently, a novel multipolarization calculation method has been proposed and applied to obtain FTIR images showing band structure in poly(L-lactic acid) and PHB spherulites with the indication of local molecular chain orientation [53]. 

Homo-FRET is a useful tool to study the interactions in living cells that can be detected by the decrease in anisotropy [106, 107]. Since commonly the donor and acceptor dipoles are not perfectly aligned in space, the energy transfer results in depolarization of acceptor emission. Imaging in polarized light can be provided both in confocal and time-resolved microscopies. However, a decrease of steady-state anisotropy can be observed not only due to homo-FRET, but also due to rotation of the fluorescence emitter. The only possibility of discriminating them in an unknown system is to use the variation of excitation wavelength and apply the... 

Scanning-angle reflectometry (SAR) together with Brew-ster-angle microscopy (BAM) [1,2] are powerful tools for the investigation of very thin layers of nanoparticles deposited or spread on the surface of a bulk material. Both reflectance methods are nondestructive and can be applied in situ, and can be realized by the same optical setup. They use the special property of p-polarized light waves that the reflectance of a perfectly abrupt, smooth interface between the medium of incidence and a... 

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