Semithin sections

IV. Cutting Sections Ultramicrotomes are designed to cut ultrathin sections, semithin sections and ultrathin frozen sections if suitably... 

Epoxy resin-embedded semithin sections of 1-2 j,m may also be used following extraction of the resin with a sodium meth(et)hoxide treatment for 5-8 min. Sodium meth(et)hoxide is prepared by saturating methanol or ethanol with sodium hydroxide pellets. 

IGSS may also be performed on cryostat sections, which may then be plastic embedded for semithin sectioning (42). 

The contour of the loaded and unloaded craze was investigated by interference optics (Doll Kdnczdl, 1990 Kdnczdl et al, 1990). Additionally the structure of the crazes was investigated by high-voltage TEM. Sections of about 1 pm were microtomed for TEM observations. Structural inspection of the craze zone was done by TEM. The fibrillar structure of a craze zone in SAN is shown in Fig. 3.14. The microstructure of this craze created in a CT sample is similar to the structure investigated in situ in strained semithin sections (Michler, 1990). 

Ling, E. A., Paterson, J. A., Privat, A., Mori, S., and Leblond, C. P., Investigation of glial cells in semithin sections. I. Identification of glial cells in the brains of young rats, J. Comp. Neurol., 149, 43, 1973. 

Schmolke C, Fleischhauer K (1984) Morphological characteristics of neocortical laminae when studied in tangential semithin sections through the visual cortex of the rabbit. Anat Embryol 169 125-132. 

Fig. 45. Immunocytochemical localization of homocysteate (HCA) with polyclonal anti-HCA antibodies. A. Staining pattern in section close to that in Fig. 44B at higher magnification. Cell (asterisk) and capillary (circle) used as landmarks in A and B. B and C. Electron micrographs from ultrathin section immediately preceding semithin section in A. The HCA-immunoreactive varicosities indicated with arrows in (A) were identified as parts of the glial sheath surrounding Purkinje cell dendrites (d) in B and C. Bars 10//m in A, 5 //m in B, 1 /tm in C. Grandes et al. (1991).

Preparation of semithin sections (up to a few micrometers thick) by ultramicrotomy, and investigation of these sections in a 1000-kV, high-voltage electron microscope (HVEM) to reveal larger particles more precisely and, thus, the true particle-diameter distribution. 

Figure 15. Strained semithin sections of rubber-modified PA (HVEM images). The deformation direction is horizontal, (a) highly deformed particles with plastically deformed matrix material in between and (b) cavitation or microvoids inside particles.

Figure 6 initiation of high local plastic deformation by cavitated core-shell particles in modified PP semithin section, deformed and investigated in a 1000 kV HVEM. (a), (b) lower and higher magnification. 

Fig. 5. Structure of a craze in PS (deformed semithin section in HVEM). (a) Fully developed craze with a clearly pronoimced fibrillation (b) domain-like structure of a pre-craze ahead of the true craze.

The methods used to prepare surfaces are covered in the next Section 2.2.2, while those used to prepare ultrathin and semithin sections and thin films are reviewed in Section 2.2.3. These three groups of preparation methods are generally applicable to various polymers, but some are more convenient for some groups of polymers, while others are better for other polymers. Sometimes, one method alone does not work very successfully to reveal all of the structural details of a material, so it is necessary to apply several techniques. Additionally, not every one of these techniques enables the realization of the maximum attainable resolution of the microscope type. 

Ultramicrotomy (including cryo-ultramicrotomy) is a standard method for the preparation of ultrathin or semithin sections, as well as very flat surfaces for various microscopic investigations. Improvements in preparation techniques over the last few decades have demonstrated that thin sections of different materials that are free from artifacts can be successfully prepared for EM investigations. Therefore, successful sectioning now depends primarily on the experience of the experimentalist rather than on the instrumentation used [14]. 

Figure 1.50 Semithin section of HIPS tilted from +3 to -3° material deformed, stained with OSO4, and investigated in HEM, deformation direction vertical, tilting axis horizontal...

Ultrathin sections are somewhat difficult to prepare and reveal only a thin layer of the material, which gives more two-dimensional information on the morphology than a three-dimensional one. Thicker semithin sections often reveal much better the size and shape of particles in polymer blends, rubber-toughened polymers, and others. Additionally, semithin sections represent bulk-tike properties better than do ultrathin sections if they contain a representative volume of the material. 

Figure 1.58 Sohematio illustration showing the effeot that ultrathin sections include only small parts of particles in a matrix, whereas semithin sections contain a representative volume ...

Figure i.59 (bottom) Frequency distributions of rubber particles in sections of different thickness of HIPS (see Fig. 1.58, top) 0.1 pm ultrathin sections show only smaller cross sections of the particles, whereas the 4 pm thick semithin sections reveal the true average particle diameter... 

Figure 1.60 Cross section of a semithin section with thickness variation between 5.2 and 6.7 pm (selectively stained semithin section embedded in epoxy, sectioning perpendicular to the section plane, HEM)...

Figure 1.64 Electron beam irradiation-induced defects in a semithin section of gelatin in HEM a focused electron beam can draw patterns in the material ...

Figure 1.65 Semithin section of polyurethane with spherulites and radial arrangement of lamellae inside ...

Figure 1.68 Tilting a deformed semithin section of PS with deformation zones (precrazes) in front of a craze in HEM the original, untilted micrograph shows the precrazes as broad bands (at the top) after tilting of 5° and 10° in the microscope (middle and at the bottom) it becomes clear that the precrazes are very narrow bands thinner than 100 nm...

Figure 1.5 Interior of a craze in PS with clear fibrillation after stretching a semithin section in an HEM, deformation direction vertical ...

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