Solid samples, electron micrographs

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. 

Figure 5. Scanning-electron micrograph of the solid sample drawn off the reaction mixture at the end of the crystallization process from the gel aged for tQ = 5 d tc = 6.5 h, fy = O- B,...

The distribution of TPA molecules over the radius of the beads of PVA-PEG was measured using a Philips Model 505 scanning electron microscope with energy dispersive X-ray analysis (EDAX) system. The secondary electron micrographs of selected solid samples were obtained. 

Figure 1.9 Scanning electron micrographs of (a) 915 nm monodisperse particles of PI, (b) crystalline sample of 420 nm monodisperse particles of P2, (c) a CP particle P3 covered with aminated silica particles attached via EDC-NHS coupling to the carboxylic acid moiety of P3, and (d) 517 nm monodisperse particles of P4. Scale bars are 2 pm except for (c) where it is 200 nm. (e) Fluorescence spectra of dispersions of PI (left curve), P2 (middle, solid line curve), P3 (dashed middle, dashed line curve), and P4 (right curve) particles, (f) Photographs of fluorescent dispersions of P1-P4 (left to right) in water. Reprinted from [279] with permission from NPG.

Lastly, the effect of the casting solvent on the domain structure of the block copolymer in the solid state was investigated. GBG-4 membrane cast from CF includes rather fine cylindrical domains (Figure 9-H), while an electron micrograph reveals more coarce domains for the same sample membrane cast from benzene (Figure 9-1). 

Latex mixtures I and II were ion-exchanged with AMBERLITE Monobed MB-1 resin 200 g of 0.2% solids latex was shaken with 20 g resin in the separatory funnel and sampled at 16, 24, and 40 hours. Figure 1 shows the electron micrographs for mixture I. The proportion of the smaller particles decreased steadily with shaking time so that only a few were seen at 24 hours. The larger particles were visible at all times, but were aggregated to a greater extent at 40... 

---