Scanning electron micrograph technique

Perhaps one obvious technique for evaluating pore structure is electron microscopy, and indeed numerous papers have been pubhshed showing visually attractive scanning electron micrographs (SEM). In fact these studies seldom provide... 

Fig. 11. Scanning electron micrographs of macroporous epoxies prepared via the CIPS technique with various amounts of 2,6-dimethyl-4-heptanone at constant curing temperature, T=40 °C...

Fig.18a-b. Scanning electron micrographs on cryo fractured surfaces of a macroporous epoxy prepared with 6 wt % hexane via the Cl PS technique showing a narrow size distribution b macroporous epoxy prepared with 7.5 wt % hexane via the CIPS technique showing a narrow size distribution. Reprinted from Polymer, 37(25). J. Kiefer, J.G. Hilborn and J.L. Hedrick, Chemically induced phase separation a new technique for the synthesis of macroporous epoxy networks p 5719, Copyright (1996), with permission from Elsevier Science... 

Precision and Accuracy. This preliminary stage was done to estimate the ways in which particle size distributions vary and to see how far they can be utilized in practical ways. The above technique was chosen to enable us to obtain some approximate results conveniently, without elaborate sample preparation. The scanning electron micrographs (Figures 6-15) show that too great an accuracy should not be expected at this stage, especially in view of the ill-dispersed nature of the particles in some cases (Figures 7 and 10). 

Most drugs and proteins are not soluble in commonly used supercritical fluids, and therefore are processed instead by the SC antisolvent technique,the most popularized being the SEDS, process which is illustrated in Fig. 9. SEDS-produced crystals can have extremely smooth surfaces, as shown by scanning electron microscopy and atomic force microscopy, and the surface may be more hydrophobic and less wettable than crystals grown under more polar conditions.A scanning electron micrograph of acetominophen crystals produced by the SEDS process is shown in Fig. 10. 

FIGURE 6 Scanning electron micrograph of the cross-section of a particle coated using a fluidized bed. Source Courtesy of Glatt Air Techniques, Inc. 

Stretched Membranes. Another relatively simple procedure for preparing microporous membranes is the stretching of a homogeneous polymer film of partial crystallinity. This technique is mainly employed with films of polyethylene or polytetrafluoroethylene which have been extruded from a polymer powder and then stretched perpendicular to the direction of extrusion.10 11 This leads to a partial fracture of the film and relatively uniform pores with diameters of 1 to 20jum. A typical stretched membrane prepared from tetrafluoroethylene is shown in the scanning electron micrograph of Figure 1.2. 

Figure 10. Scanning electron micrograph of particulates (left) and the computer-generated binary image (right). With computer control of the microscope stage and electron beam, the particles can be individually characterized as to composition and size distribution. With appropriate detector configurations, the computer can automatically identify the particles, size them, and control the SEM to determine the composition of the particulates. These methods are currently in common use only for separated dried particulates, although, in principle, similar techniques could be used for characterization of particulates in suspension.

Figure C2.17.3. Close-packed array of sub-micrometre silica nanoparticles. When nanoparticles are very monodisperse, they will spontaneously arrange into hexagonal close-packed structure. This scanning electron micrograph shows an example of this for very monodisperse silica nanoparticles of 250 nm diameter, prepared in a thin-film format following the techniques outlined in [236].

---