Specimen preparation ultrathin sectioning

It was not possible to prepare ultrathin sections with an ultramicrotome, even after osmium tetroxide fixation (24). The EO segment is hydrophilic, and therefore the specimens were too ductile for ultrathin sectioning. Furthermore, there was no suitable liquid which is a common poor solvent for both segments on which to float the ultrathin sections in order to mount them on the microscope mesh. 

In literature the following methods of preparation of polymer material specimen and studying their morphology are described methods of ultrathin section and films with contrasting of osmium tetroxide (10.11). method of replication of the brittle fractur-ed surface (11.12) oxygen and chemical etch of the polished surface or the fractured surface with the following replication for electron microscopy (11. 

For the observation of biological material in the electron microscope it is best to have a thin specimen with enough contrast. It was therefore of primary importance to make ultrathin sections (< 0.1 jam) of the material, which can only be done after a whole series of preparation techniques have been applied. Some specimens, however, are so thin that they need not be sectioned, but can be investigated by means of negative staining [1]. 

There are multiphase polymers where OM and SEM techniques cannot fully describe the microstructure due to a combination of small particle size (less than 0.5 /xm) and good adhesion between the dispersed phase and the matrix. Additionally, broad particle size distributions are often encountered, and in these cases a combination of techniques is required to describe the microstructure. TEM requires ultrathin specimens, about 50-500 nm or less in thickness, which are prepared by film casting or ultrathin sectioning. Films formed by casting or dipping methods provide a much easier specimen preparation method than ultrathin sectioning of bulk plastics. However, a major question in such studies is always whether the microstructure is the same as in bulk polymers of industrial interest. Specific stains are often required to provide contrast between the dispersed phase and the matrix pol)m[ier. 

Microscopy techniques can be used to evaluate the size and distribution of particles added to polymer fibers, such as metals that modify the physical, mechanical, or electrical properties. In general, ultrathin sections are examined in either STEM or TEM modes to reveal the particles within the polymer. Energy (EDS) and wavelength dispersive x-ray spectroscopy (WDS) methods are used to map for various elements in order to establish the relation between the particle morphology and chemical composition. A specimen preparation method for x-ray analysis in the SEM is to use a trimmed block face, which remains after cutting thin sections, or to study a thick section. An example of such a study is described below. 

Cellulose nitrate and cellulose acetate (CA) were among the first asymmetric, reverse osmosis membranes to be produced [121]. Plummer et al. [122] described 13 specimen preparation methods for observation of CA membrane structures. They pointed out the lack of contrast in epoxy embedded sections and that one of the best stains, osmium tetroxide, reacts with the polymer. Freeze fractured membranes were found by these authors to be of questionable value. In our experience, if care is taken, SEM study of fractured membranes can provide an informative view of the structure even though some structures collapse, and their sizes cannot be accurately determined. A method found acceptable was ultrathin sectioning of gelatin embedded wet membranes (TEM). The structure of CA membranes was shown by replication [123] and SEM [124]. 

Sample preparation Very critical. Ultrathin specimens needed (Section 9.3 Table 9.4). 

Finally, in order to verify molecular-length scale healing, an energy dispersive spectroscopy (EDS) (15 kV, super-ultrathin window (SUTW) Saphire detector, amplification process time (AMPT) of 25.6 ps) analysis was conducted using a Hitachi 3600 N scanning electron microscope equipped with an EDAX genesis detector. The rationale was that if the CP molecules diffused into the PSMP matrix, the chemical composition near the interface will show a certain gradient. In this study, a specially prepared EDS specimen was used. To prepare the EDS specimen, a SENB specimen made of pure PSMP was fractured and a very thin layer of CP was placed in between the fractured surfaces. Next, the EDS specimen was healed as described in Section 6.1.1. An EDS analysis was conducted at and around the healed interface of the EDS specimen. 

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