Chemical staining, thin sections

Fig. 21. Morphology of an injection-molded specimen of a star-block copolymer with a PS content of 74% with lamellar arrangement of PS and PB lamellae before and after deformation, (a) PS and PB lamellae before deformation (b) Plastically stretched PS and PB lamellae deformed in parallel direction to lamellar orientation (a, b tern micrc aphs of chemically stained thin sections, PB lamellae appear dark arrow shows direction of tension) Frequency distributions of thicknesses of PS lamellae (c) before and (d) after deformation. From Ref. 60.

Ductile behavior can be studied using a modification of Method 2, a bending experiment see Fig. 1.53. A bent specimen is illustrated in Fig. 1.53(a), and a result of deformed rubber-toughened PVC is shown in a TEM micrograph in Fig. 1.53(b). The sample from the loaded area is a chemically stained thin section prepared by ultramicrotomy, showing fibrillated crazes between the acrylic rubber particles (both stained dark). 

Transmission electron micrographs of HIPS (A) osmium-stained thin section showing salami structure, with polystyrene sub-inclusions embedded in (black) rubber phase, in a matrix of polystyrene (B) unstained thicker section stretched on the microscope stage. The unloaded specimen (A) has largely recovered, and shows compressed crazes. The stressed sample (B) shows extended craze fibrils and fibrillated rubber. (Micrographs by courtesy of R. C. Cieslinski, Dow Chemical USA.)... 

Fig. 2 Generation of spectroscopic FTIR images, a Native sample, here a thin section of biological tissue, b FTIR spectra are collected at every pixel of the native sample. Bad spectra, e.g. from areas outside the sample, have already been removed, c Good spectra have been subject to a chemometric cluster analysis. Pixels are color-coded according to the cluster membership (spectral staining). Slightest chemical differences across the sample are now clearly revealed...

In thin sections from the oil zone, we observe that calcite II is associated with oil staining. On the other hand, in the water zone type III calcite shows no association with oil. Below the water-oil contact, in zones where there is no or only scarce calcite cement development, mechanical and chemical compaction was the main diagenetic process responsible for porosity loss. 

Some aspects of morphology can be observed directly by transmission electron microscopy of stained and ultramicrotomed thin sections. The most successful staining method, developed by Kato, makes use of osmium tetroxide, which attacks the double bonds in diene type polymers. The OSO4 staining technique can also be used with other active groups, such as polyurethanes.Many saturated or nonreactive polymers are not easily studied by transmission electron microscopy, unfortunately, because they cannot be stained. Other aspects of morphology, such as phase continuity and interface characteristics, are best determined by combining chemical and dynamic mechanical spectroscopy methods with electron microscopy. 

Figure 21.8. Primary hBMSC chondrocyte (2 1 seeding ratio) responses inside chitosan-coated alginate capsules with chemically linked GRGD peptide at 28 days. The panel of images are thin sections of capsules that have been stained with alcian blue and Sirius red to indicate presence of collagen and proteoglycan extracellular matrix. GRGD induces a tissue formation response.

Figure 5.40. Transmission electron microscopy thin section of phosphotungstic acid stained cryosections of an as extruded (A) and deep drawn (B) coextruded film constructed of toughened nylon/barrier resin/tough-ened nylon. (From Wood [186] used with permission of the American Chemical Society Rubber Division.)...

The mostly used and most successful method to prepare polymers for TEM inspection is ultramicrotomy (including cryoultramicrotomy) in combination with chemical staining. It is the standard method for the preparation of ultrathin and semi-thin sections as well as very flat surfaces of plastics and biological and biomedical objects for various microscopic investigations. Improvements in preparation techniques over the past few decades have demonstrated that thin sections of different materials that are free from artefacts can be successfully prepared for electron microscopic investigations. 

Fig. 2.19 TEM micrographs of (a) a sphemlite centre in a thin film of high density polyethylene stained with RUO4, (b) section of polyethylene-atactic polypropylene block copolymer stained with RUO4. Reproduced with permission (a) from Figure 15 in Trent, Scheinbeim and Couchman, Macromolecules, 1983, 16 589-598 (Copyright 1983) American Chemical Society, (b) fi om Figure 3 in Hong, Copyright (2001) with permission from Elsevier...

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