Microtomy films

The preparation, which is rapid if it concerns dispersing the crushed catalyst on an amorphous carbon film, may take several hours for microtomy. The analysis of a sample in transmission electron microscopy requires several hours of observation if the aim is to ensure that the results are representative. This is particularly important when subsequently seeking to determine particle size distribution histograms. Reliable values of the average size and of the width of the distribution can only be obtained taking into account a number of particles greater than 100. 

An extension to normal ultramicrotomy is cryouT tra-microtomy, in which, as the name suggests, the temperature of both the specimen and the knife is reduced. The temperature depends on the glass transition temperature of the material. A sample such as polymer film on aluminum substrate can be prepared only in this way, and Figure 5 shows the aluminum foil, an oxide layer, and the polymer coating. 

This method has been applied to experiments of multiple internal reflection infrared spectroscopy on thin films of commercial polyethylene [120]. It is known that optical microtomy can be achieved by changing the incidence angle of the incoming beam. Structural depth profiling has then be performed thus allowing to probe the ordered-disordered structure of such films (Figure 3-32). 

Specimen preparation for TEM generally in-voles the formation of a thin film of the material less than 100 nm thick. The methods used for this preparation depend upon the nature of the polymer and its physical form. In the case of thick or bulk specimens, microtomy is generally used. In the case of solutions, powders or particulates, simpler methods can provide a thin, dispersed form of the material. Three types of simple preparations will be described later in this section dispersion, disintegration and film casting. The more complex methods such as microtomy, replication, etching and staining will be described in other sections of this chapter. 

Specimens for microtomy must either be cut to fit in the chuck of the microtome and be self supporting, or they must be embedded in a supporting medium. Pieces of molded or extruded plastics are trimmed to fit the chuck using small saws and razor blades. In the case of films and fibers, however, the samples must be embedded in a resin for both support and... 

Sectioning is one of the most widely used methods in the preparation of polymers for electron microscopy. Microtomy permits the observation of the actual structure in a bulk material which is not possible by methods such as thin film casting or surface replication. Polymers (in common with biological tissues) require care in handling, embedding in resins for support and addition of stains to enhance contrast in the TEM. 

Model cast films are made with no possibility of damage or deformation during specimen preparation by microtomy or fracture. 

A study of a PS-PB block copolymer showed variation in craze behavior as a result of rubber particles added to modify the otherwise brittle, glassy polymers. Such copolymers were studied under the high strain of physical laboratory testing where the polybutadiene in the copol)mier was stained with osmium tetroxide prior to microtomy [333]. The brittle behavior of the glassy polymers was shown by TEM and STEM to be modified by the rubber particles which provide toughening by control of the craze behavior. In a study of the craze behavior in isotactic polystyrene [146], films of polystyrene were drawn from dichlorobenzene solution and cast onto glass microscope slides, followed by... 

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