Osmium tetraoxide staining

Electron Microscopy. For morphological characterization electron microscopy was extensively used in conjunction with the osmium tetraoxide staining method. 

Figure 41 TEM of osmium tetraoxide stained clusters presented on a grid. This sample was obtained from the high molecular weight fraction of methanol soluble decantate.

The blends are frozen in liquid nitrogen and then microtomed and stained with osmium tetraoxide, which stains only unsaturated elastomers. 

Visualization of the micromorphology with transmission-electron microscopy (TEM) on ultrathin cuts after staining with osmium tetraoxide... 

Moreover, in the 76 19 5 wt% blend, TEM reveals at the interface a black layer due to SEBS stained by reaction with osmium tetraoxide (Figure 20.6a). In the 72 18 10 wt% blend (Figure 20.6b) the excess of SEBS forms inclusions into HDPE. It is likely that crystallization of sPS, which occurs at 225 CC, forces SEBS to segregate from the sPS domain, thus favoring its inclusion in the HDPE phase. 

Measurements of particle size in the final product can be done with a Coulter Counter or electron microscopy by using osmium tetraoxide to stain the rubber particles. This staining also allows visual observation of the rubber morphology as shown for HIPS and ABS in Figure 5. The polybutadiene rubber is stained dark with osmium tetroxide and the continuous polystyrene phase is the light background. What is observed is somewhat circular rubber particles with polystyrene occlusions. These occlusions extend the effective rubber phase volume for better use of the rubber. Particle size varies as well as the density of the rubber particle. 

Figure 5 depicts the complementary hydrogen bonding structure of 20 and 21 that was predicted from the x-ray diffiaction data. The TEM photograph of a dilute ethylacetate gel (stained by osmium tetraoxide) that used the same mixture is shown in Fig. 6. It shows occasional necking-like patterns. This necking is probably caused by the twisting of the tape-like assembly formed by supplemental hydrogen bonding.

Osmium (VIII) tetraoxide (Os + 40 —> OsO ) is a yellow crystal and probably the most important compound used as an oxidizing agent, as a biological stain in microscopy, and to detect fingerprints. 

---