Osmium tetroxide vapor

The Smith technique consisted of fixing the smear in osmium tetroxide vapor, immersion in HCI, mordanting in dilute formaldehyde, and staining with aqueous basic fuchsin. The method was said to possess certain advantages over the procedure of Robinow. 

Stain embedded sections lightly in uranyl acetate and lead citrate (optional). Frozen sections may be stained with osmium tetroxide vapor. Staining with OSO4 or uranyl acetate may be conducted without obscuring the gold particles. Wash and examine under the electron microscope. 

The electron micrographs of the various ERL-4221-CTBN systems were prepared with the osmium tetroxide technique (3). The castings were stained by reaction with osmium tetroxide vapors for 24 hours. Ultrathin specimens, approximately 1000 A thick, were cut with the Reichert OMU2, ultramicrotome equipped with a diamond knife and were stained again for one hour. The osmium tetroxide selectivity stained the rubber phase, while the epoxy remained unaffected, revealing many structural features in the polyphase systems with excellent contrast and... 

Osmium tetroxide vapors Brown/black spots 3,95... 

Transmission electron microscopy (TEM) was used to study the morphology of the cross-linked matrix and to determine the size of the rubber domains. Specimens were microtomed and exposed to osmium tetroxide vapor to stain the rubber-rich portions of the network. The fracture surfaces of specimens were coated with gold and examined with a scanning electron microscope (SEM). 

Methods. Thin films of block copolymers were cast from their cyclohexane solutions at 20°C, and the films were observed under a polarizing microscope. Ultra thin films (50-500 nm) were cast from the same solutions onto sheet meshes at 20 °C and stained by osmium tetroxide vapor they were then observed under a Hitachi HU-11 electron microscope. 

Morphology. Ultrathin cast films of polystyrene and PTHF homopolymers stained by osmium tetroxide vapor were examined by electron microscopy. Only the PTHF was stained. 

Osmium tetroxide vapors are poisonous and result in damage to the respiratory tract and temporary damage to the eyes. 351 Use OSO4 powder only in a well-ventilated hood with extreme caution. 

Osmium tetroxide staining can be accomplished by exposing a sample to osmium tetroxide vapor for a week, or by soaking overnight in a 1 %... 

The acute toxicity of osmium tetroxide is high, and it is a severe irritant of the eyes and respiratory tract. Exposure to osmium tetroxide vapor can damage the cornea of the eye. 

Early results with cryomicrotomes were described by Cobbold and Mendelson [80]. Polyurethane elastomer, a blend of crystalline and noncrystalline polymers, showed spherulitic textures after sectioning at about -70°C. Injection molded polypropylene (PP) was also sectioned at about -70°C, while polytetrafluoroethylene (PTFE) was sectioned at much lower temperatures. The authors concluded that the technique, though difficult, had potential. Extruded styrene-butadiene-styrene (SBS) copolymer was prepared by cryosectioning with a diamond knife in liquid air at —85 to —115°C, followed by osmium tetroxide vapor staining for one hour [81]. This method revealed the alternating sequence of the polystyrene and polybutadiene lamellae. Odell et al. [82] prepared extruded triblock copolymer by first chemically hardening the polybutadiene, with osmium tetroxide, followed by cryoultramicrotomy to produce 30 nm thick sections which showed fine structure details. Parallel polystyrene rods were observed in the SBS copolymer. Ultramicrotomy and selective staining with osmium tetroxide was also used in the preparation of a binary blend of PP and thermoplastic rubber [83]. 

Some examples of osmium tetroxide staining are worthwhile to discuss as they describe staining methods for specific polymers. Osmium tetroxide vapor was used to stain and harden (3 days) a thin film of a two phase blend containing crystalline polychloroprene [91]. The spherulitic texture was observed, likely by a combination of staining due to the unsaturation present and due to differential absorption by the crystalline and amorphous regions in the spherulites as the crystalline... 

Figure 17.6a is a TEM image of an ultrathin section of the HIPS sample that had been stained with osmium tetroxide vapor [64]. The aim of such staining was to render the internal stracture of the HIPS visible by selectively depositing a heavy-metal component in the butadiene-rich phase (or in the component with C=C unsaturated bonds). The image showed the typical salami stmcture of the sample, while the butadiene-rich phase and the crazes appeared as dark areas. This imaging was especially important because it provided information as to how the crazes evolved, wandered, and were eventually stopped by the presence of the salami particles. 

Figure 17.8a is the TEM image of a styrene/butadiene star block copolymer containing 74% (by volume) styrene. The nanostmctured morphology arises from the fact that the constituents - that is, polystyrene (PS) and polybutadiene (PB) chains -are connected chemically by covalent bonds which do not permit a macroscopic segregation of the polymer chains. Due to the presence of a unique molecular architecture of the copolymer, the star block copolymer was found to show a cocontinuous arrangement of the nanostmctures [69-72]. The star block copolymer specimen was treated -with osmium tetroxide vapor prior to TEM imaging such treatment... 

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