Techniques and Methods on Micrographs

As has already been shown, the method of preparation and the investigation technique for polymers can influence the appearance of morphology of the particular polymer. In addition, one must consider whether varying the preparation methods and microscopic techniques can improve or even deteriorate the visibility of structural details. Some examples of the practical importance of sample preparation and of microscopic technique that can strongly influence the visibility of structures in the micrographs are described in the following sections. 

---

In this introductory section of Part i, Sections 1.2 and 1.3 present basic connections between chemicai structure and morphoiogy with an overview of the hierarchicai structure of poiymers. Section 1.4 gives a brief characterization of the mechani-cai behavior of poiymers. For a better understanding of the micrographs, a short description of the different microscopic investigation techniques and the sample preparation methods is presented in Chapter 2 of this part (Sections 2.1 and 2.2). Techniques and methods to study deformation structures, micromechanicai mechanisms, and fracture details are the content of Section 2.3. Possibie influences on the morphoiogy due to sample preparation or microscopic investigation are considered in more detaii in Chapter 3. 

FIGURE 2.6 Effect of the type of the method of preparation on morphology and particle size of lipospheres. Optical micrographs of microspheres produced by (A) melt dispersion technique and (B) solvent evaporation technique. Lipospheres were constituted of tristearin glyceryl monostearate 2 1 (w/w) and prepared in the presence of 1% polyvinyl alcohol. Bar corresponds to 292 and 162 pm in panels A and B, respectively. (C) Frequency distribution plot of microspheres produced by melt dispersion (A) and solvent evaporation ( ) technique. Data are the mean of three different microsphere batches. 

Electron Microscopy The sample preparation was based on Kato s (10) osmium tetroxide staining technique and a two-step sectioning method. The specimens were exposed to O5O4 vapor and cut with a LKB ultratome III to get a 0.1 y slice. The electron micrographs were taken with an AEI 6B and a Phillips 300 transmitting electron microscope with a magnification of 95,000. 

Table 2. Comparison of volume fraction and inter pore distance, IPD, for macroporous epoxies prepared with 6 and 7.5 wt % hexane via the CIPS technique caicuiated either with the classical method from SEM micrographs or based on density measurements...

Transmission electron microscopy (TEM) can provide valuable information on particle size, shape, and structure, as well as on the presence of different types of colloidal structures within the dispersion. As a complication, however, all electron microscopic techniques applicable for solid lipid nanoparticles require more or less sophisticated specimen preparation procedures that may lead to artifacts. Considerable experience is often necessary to distinguish these artifacts from real structures and to decide whether the structures observed are representative of the sample. Moreover, most TEM techniques can give only a two-dimensional projection of the three-dimensional objects under investigation. Because it may be difficult to conclude the shape of the original object from electron micrographs, additional information derived from complementary characterization methods is often very helpful for the interpretation of electron microscopic data. 

Some of the more noteworthy EM techniques which were first described prior to 1990, deserve mention because of their contribution to the advancement of food structure knowledge. The utility of ciyo-SEM in food systems was clearly illustrated by Saigent [57] including over 40 micrographs of diverse food systems as visualized by ciyo-SEM techniques. Since that time numerous papers can be found in the literature utilizing ciyo-SEM methods. An ever expanding list of unique and novel applications to new foods has come from the papers of Heertje and his co-workers and is summarized by Heertje [58]. Here we must focus on the newer techniques which have been developed in recent years the first of these is environmental SEM. 

A transmission electron micrograph of a craze in a thin film of poly(styrene-acrylo-nitrile), shown in Fig. 1 a, will serve to introduce the principal microstructural features of crazes. The direction of the tensile stress is marked and it can be seen that the craze grows with the primary direction of its fibrils parallel to this tensUe stress and with the interfaces between the craze and the nearly undeformed polymer matrix normal to the stress. Since the overwhelming portion of the experiments to be reviewed here rely on the use of thin film deformation and transmission electron microscopy techniques, a brief review of the general methods of these experiments is in order. 

---