Chlorosulphonation, staining

Selective chemical staining of the rubber phase of the samples using chlorosulphonic acid and osmium tetroxide, preparation of ultrathin sections (about 0.1 xm thick) in a cryoultramicro-tome, and investigation of the sections by conventional transmission electron microscopy (TEM). 

The staining technique for TEM uses a material that absorbs electrons and preferentially attaches itself to or reacts with certain regions of the polymer rather than other regions. Materials frequently used are uranyl acetate and osmium tetroxide. For polyethylene the technique of chloro-sulphonation can be used. In this method, which involves immersing the sample in chlorosulphonic acid, the electron-absorbing material becomes attached to lamellar surfaces, so that lamellae (see section 3.4.2) with their planes parallel to the direction of the electron beam become outlined in black in the micrographs. 

Figure 3. Morphology by transmission electron microscopy of the VLDPE of Figs. 1 and 2, after staining/fixation by chlorosulphonation. The inset shows a 1.6 times magnified view of a more severely treated sample revealing the internal morphology of the CSDs.

Figure 10.15 Banded spherulite in low-density polyethylene after staining with chlorosulphonic acid. Although the lamellar structure is well resolved at the centre of the object, in other regions morphological detail is less distinct.

Figure 10.16 Structural details revealed by staining, in this case showing lamellar detail in cross-linked polyethylene (chlorosulphonation).

The staining ability of chlorosulphonic acid of the amorphous component of polyethylene was first reported by Kanig (1973). The strong acid diffuses... 

The lamellar structure is best studied using TEM. Let us take polyethylene. Two methods of preparation are commonly used staining with chlorosulphonic acid/uranyl acetate and etching with permanganic acid. 

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