Size methods electron microscope

Porosity and surface area are routinely measured by nitrogen absorption-desorption, mercury intrusion, and low-angle X ray. The electron microscope (EM) provides direct visual evidence of pore size and pore-size distribution. Thus, a combination of EM and conventional methods of pore-size measurement should provide reliable information on the pore structure of polymers. 

Kaye, An Electron Microscope Method for the Determination of the Particle Size Distribution and Particle Shape of Colloidal and Ball-Milled Lead Azide , PATR 2133 (1955) 25a) A.T. 

The large size of CPOs allows their direct observation. For this purpose, scanning tunneling microscopy (STM) is the best method [32,34]. Electron microscopic analysis is used for phthalocyanine 3 and its derivatives however, most of the porphyrin derivatives are decomposed by electron beam irradiation. Presently, although only a limited number of researchers are able to perform atomic-scale resolution measurement, this powerful analytical method is expected to be used widely in the future. The author reported a summary of STM studies on porphyrins elsewhere [34]. 

Herein we briefly mention historical aspects on preparation of monometallic or bimetallic nanoparticles as science. In 1857, Faraday prepared dispersion solution of Au colloids by chemical reduction of aqueous solution of Au(III) ions with phosphorous [6]. One hundred and thirty-one years later, in 1988, Thomas confirmed that the colloids were composed of Au nanoparticles with 3-30 nm in particle size by means of electron microscope [7]. In 1941, Rampino and Nord prepared colloidal dispersion of Pd by reduction with hydrogen, protected the colloids by addition of synthetic pol5mer like polyvinylalcohol, applied to the catalysts for the first time [8-10]. In 1951, Turkevich et al. [11] reported an important paper on preparation method of Au nanoparticles. They prepared aqueous dispersions of Au nanoparticles by reducing Au(III) with phosphorous or carbon monoxide (CO), and characterized the nanoparticles by electron microscopy. They also prepared Au nanoparticles with quite narrow... 

J du Plessis, LR Tiedt, AF Kotze, CJ van Wyk, C Ackerman. A transmission electron microscope method for determination of droplet size in parenteral fat emulsions using negative staining. Int J Pharm 46, 1988. 

In addition to fluorescence methods, another study [27] developed a method to permit electron microscopic localization of Ras anchor domains on cytoplasmic membrane surfaces by immunogold labeling. The particle neighbor distances can be analyzed to obtain information about possible domain structure. Expressing H-Ras and K-Ras in baby hamster kidney cells, a nonrandom particle distribution was obtained from which the estimated mean raft size was 7.5-22 nm and about 35% of the membrane area consists of rafts. The same technique applied to cells that had been incubated with [3-cydodextrin to reduce cholesterol produced completely random distributions of H-Ras. This cholesterol dependence suggests some type of coupling of rafts across the inner and outer membrane leaflets. 

Microscopic examination permits measurement of the projected area of the particle and also enables an assessment to be made of its two-dimensional shape. In general, the third dimension cannot be determined except when using special stereomicroscopes. The apparent size of particle is compared with that of circles engraved on a graticule in the eyepiece as shown in Figure 1.3. Automatic methods of scanning have been developed. By using the electron microscope 7, the lower limit of size can be reduced to about 0.001 pan. 

Although it is sometimes possible to view pores with an electron microscope and to obtain a measure of their diameter, it is difficult by this means to measure the distribution of sizes and impossible to measure the associated surface area. Adsorptive methods are used instead, employing some of the theories of adsorption explained previously. 

Byers, R.L, Davis, J.W., White, E.W., and McMillan, R.E. (1971) A computerized method for size characterization of atmospheric aerosols by the scanning electron microscope. Environ. Sci. Technol, 5, 517-521. 

The diameters of the pores of the surface layer of Loeb-Sourlrajan-type cellulose acetate membranes have been reported by several authors (1-6). The reported values of the diameters cover the range between 10 A and 60 A. For electron microscopic observations, the replication method must be used. In order to obtain the excellently contrasted Images the surface of the sample Is shadowed with heavy metals In vacuum. In many cases the Pt-Pd alloy has been used as a pre-shadowlng metal. But the resolution of the Pt-Pd replica Is at the level of about 50 A, since the size of the evaporated particles Is between 20 X and AO X (7, 8, 9). If the pore sizes are In the range of the above-mentioned level, we cannot observe them. 

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. 

Fig. 9.4.7 Electron microscopic images of Mg small particles prepared by different methods and their size histograms. (A) Mg fine powders produced by a conventional gas-evaporation method with Ar at 4 kPa. (B) Mg fine particles produced by a matrix isolation method with Ar at 300 Pa in tetrahydrofuran. (C) Mg ultrafine particles produced by a matrix isolation method with He at 1.3 kPa in tetrahydrofuran. The scale bar for (C) is the same as for (B). Abscissa at top (n) is a rough estimate of the number of Mg atoms in a single particle whose diameter is represented by logarithm of diameter (nm) in the bottom scale. Ordinate (N ) is a normalized number of particles in a unit size width. (From Ref. 4.)...

The mean primary particle sizes of pigment blacks he in the range 10-100 nm specific surface areas are between 20 and 1000 m2/g. The specific surface area, determined by N2 adsorption and evaluation by the BET method [4.29], is often cited as a measure of the fineness of a black. Blacks with specific surface areas >150 m2/g are generally porous. The BET total specific surface area is larger than the geometric surface area measured in the electron microscope, the difference being due to the pore area resp. the pore volume. 

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