Specimen preparation method optical microscopy

The increased use of optical and electron microscopy applied to polymer research has been the result of widespread acceptance of the techniques and extended property requirements of the polymer materials. It is known that the structures present in a polymer reflect the process variables, and further that they greatly influence the physical and mechanical properties. Thus, the properties of polymer materials are influenced by their chemical composition, process history and the resulting morphology. Morphological study involves two aspects prior to the study itself selection of instrumental techniques and development of specimen preparation methods. Structural observations must be correlated with the properties of the material in order to develop an understanding of the material. 

Just as important as the proper use of the microscope is the specimen preparation. When using transmitted-light microscopy, it is necessary to prepare thin samples, about 5-50 pm thick. This is also true even for transparent polymers because of the small depth of field of an optical microscope. If information is required about an inner part of the material, the only course of action is to cut a thin section with a microtome. Melt-pressed films can be prepared by melting the polymer and squeezing it between two glass slides to make it thin. Many of the generally known specimen preparation methods are applicable to polymers. A recent overview of all methods as a useful tool for polymers is given in [Ij. 

Once the objective of the experiment is known and the specimens selected for study, the next major step is the selection of the microscopy techniques and the specimen preparation methods required to image the polymer structures of interest (Table 6.2). If lamellar crystals must be evaluated, for instance, there is no point in considering most optical techniques as they will only provide an overview of these structures. Comparisons are made in this section regarding the various techniques, in both the text and tables, as an aid in this selection process. Observations of... 

The methods of specimen preparation for optical microscopy are various. In fundamental polymer studies, thin films of polymers can be crystallized between a slide and cover slip. In an apparatus such as a hot stage attached to a microscope, the crystallization process can be followed as it occurs. However, two features must be taken into account, firstly that in specimens where large spherulites form, their centres are confined to a narrow plane and are not distributed in depth as they would in a bulk specimen. Also, nucleation of crystal growth may be enhanced on the surface of the slide and cover slip, and transcrystalline layers, rather than the spherulitic structure of the bulk material, may form. 

Replication is one of the oldest methods used for the production of thin TEM specimens and it is also used for specimen preparation for optical microscopy and SEM. The procedure was first introduced by Bradley [426, 427], and it is well documented in texts on specimen preparation [428, 429]. Replicas have the surface characteristics or topography of the original specimen without the need to directly image beam sensitive materials. Reflected light microscopy of polymer surfaces is often difficult because glare from the surface limits visible detail, although... 

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