Optical and Electron Microscopy

Transmission electron microscopy (TEM) can resolve features down to about 1 nm and allows the use of electron diffraction to characterize the structure. Since electrons must pass through the sample however, the technique is limited to thin films. One cryoelectron microscopic study of fatty-acid Langmuir films on vitrified water [13] showed faceted crystals. The application of TEM to Langmuir-Blodgett films is discussed in Chapter XV. 

Colloidal particles are often too small to permit direct microscopic observation. The resolving power of an optical microscope (i.e. the smallest distance by which two objects may be separated and yet remain distinguishable from each other) is limited mainly by the wavelength A of the light used for illumination. The limit of resolution 8 is given by the expression 

Owing to its large numerical aperture, the depth of focus of an optical microscope is relatively small (c. 10 /xm at x 100 magnification and c. 1 /xm at x 1000 magnification). This is not always a 

Particle sizes as measured by optical microscopy are likely to be in serious error for diameters less than c. 2 pm, although the limit of resolution is some ten times better than this (see Table 3.1). 

In addition to the question of resolving power, the visibility of an object may be limited owing to lack of optical contrast between the object and its surrounding background. 

Two techniques for overcoming the limitations of optical microscopy are of particular value in the study of colloidal systems. They are electron microscopy36-37, in which the limit of resolution is greatly extended, and dark-field microscopy, in which the minimum observable contrast is greatly reduced. 

A similar Pake line-shape would arise for a pair of like spins interacting by magnetic dipole coupling, as shown by equation (2.9), but in this case observed lines are usually broadened even in the absenee of motion because each spin in a solid does not interact with only one neighbouring spin but with a large number of surrounding spins. 

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The specific surface area of a solid is one of the first things that must be determined if any detailed physical chemical interpretation of its behavior as an adsorbent is to be possible. Such a determination can be made through adsorption studies themselves, and this aspect is taken up in the next chapter there are a number of other methods, however, that are summarized in the following material. Space does not permit a full discussion, and, in particular, the methods that really amount to a particle or pore size determination, such as optical and electron microscopy, x-ray or neutron diffraction, and permeability studies are largely omitted. 

Pohl D W 1991 Soanning near-field optioal miorosoopy (SNOM) Advances/n Optical and Electron Microscopy yo 12, ed R Barer and V E Cosslett (London Aoademio)... 

In order to define the extent of emissions from automotive brakes and clutches, a study was carried out in which specially designed wear debris collectors were built for the dmm brake, the disk brake, and the clutch of a popular U.S. vehicle (1). The vehicle was driven through various test cycles to determine the extent and type of brake emissions generated under all driving conditions. Typical original equipment and aftermarket friction materials were evaluated. Brake relines were made to simulate consumer practices. The wear debris was analyzed by a combination of optical and electron microscopy to ascertain the asbestos content and its particle size distribution. It was found that more than 99.7% of the asbestos was converted to a nonfibrous form and... 

C. Colliex. In Advances in Optical and Electron Microscopy. (R. Barer and V.E. Cosslett, eds.) Academic Press, 1984, Volume 9. This chapter contains a concise, but detailed, treatment of EELS with significant references to the major studies done. 

The techniques, instrumentation and underlying theory of optical microscopy for materials scientists have been well surveyed by Telle and Petzow (1992). One of the last published surveys including metallographic techniques of all kinds, optical and electronic microscopy and also techniques such as microhardness testing, was a fine book by Phillips (1971). 

The study of filler distribution by the methods of optical and electronic microscopy has shown that in all compositions obtained by method 4 the filler is distributed rather uniformly as in an individual polymer. In the mixtures of incompatible polymers, obtained by methods 1 and 2, the filler is distributed nonuniformly and there are zones of high concentration of the filler and almost empty ones. The size of such zones is close to the size of polymer regions known for mixtures of thermodynamically incompatible polymers — 1 to 10 p. 

Humphries, D.W. Mensuration Methods in Optical Microscopy, ADVANCES IN OPTICAL AND ELECTRON MICROSCOPY. Barer. R. and Coslett. V.6., Ed. 1969, 3, 33-95, Academic Press, New York. 

Until quite recently the very initial stages of metal deposition were difficult to characterize in detail by structure- and morphology-sensitive techniques. As a consequence and for practical purposes - multilayers were more useful for applications than monolayers - the main interest was focussed onto thick deposits. Optical and electron microscopy, ellipsometry and specular or diffuse reflectance spectroscopy were the classic tools, by which the emerging shape of the deposit was monitored [4-7],... 

A.W. Newman and H.G. Brittain, Optical and electron microscopies. In Physical Characterization of Pharmaceutical Solids, Marcel Dekker, New York, 1995, pp. 127-156 Chapter 5. 

In determination of health hazards due to exposure to fibre inhalation, the feasibility of using the inertial spectrometer (INSPEC) as a sampler that separates fibres according to their aerodynamic diameter was explored. Optical and electron microscopy demonstrated a satisfactory size separation of the fibres and alignment along the flow lines. 16 refs. 

In order to control the quantity of fullerene, contacting biological objects, FoS were obtained by evaporation of saturated solution of C60 in hexane introduced in the wells of 96-well culture plates ( Sarstedt ). Twenty-five microliters of solution was applied to each well and evaporated at 20-25 °C, after which the procedure was repeated several times to obtain a desirable concentration of fullerene (10, 20, and 30pg/cm2). Application of such volume allows obtaining a surface, covered with fullerene on the bottom and partly on the walls of a well at a high less than 2 mm. Microscopic investigations (optical and electronic microscopy) have shown that the surface was covered irregularly fullerene formed the isolated clusters, so that obtained fullerene films were not the real films, but rather isolated clusters of fullerene molecules (data not shown). However, it should be noted that their dimensions were smaller than those of cells and each cell covered several such clusters. 

Some examples of direct measurement of the crystal distortion during the reaction by optical and electron microscopy, IR absorption, and x-ray diffraction have been reported (see references in Ref. 311). The observed (anisotropic) changes in lattice parameters have been used for calculating the kinetic parameters of the transformations. For some reactions, it was possible to follow by x-ray diffraction the change in lattice parameters and also in atomic coordinates, so the relaxation could be observed at atomic level. 

Ballantyne et al. concluded that these experiments demonstrated a much greater degree of safety for CR and less (almost nonexistent) damage to the eye than CN. Colgrave et al. examined the fine structure of exposed rat lungs by optical and electron microscopy... 

Membrane filters are particularly useful when surface analytical techniques, such as optical and electron microscopy and X-ray fluorescence analysis, are to be used subsequent to collection, because most of the particles remain on the surface of the filter. 

Particle size measurement is one of the essential requirements in almost all uses of colloids. However, our discussion in Section 1.5 makes it clear that this is no easy task, especially since even the definition of particle size is difficult in many cases. A number of techniques have been developed for measuring particle size and are well documented in specialized monographs (e.g., Allen 1990). Optical and electron microscopy described in the previous section can be used when ex situ measurements are possible or can be acceptable, but we also touch on a few nonintrusive methods such as static and dynamic light scattering (Chapter 5) and field-flow fractionation (see Vignette II Chapter 2) in other chapters. 

The size distributions of the particles in cloud samples from three coral surface bursts and one silicate surface burst were determined by optical and electron microscopy. These distributions were approximately lognormal below about 3/x, but followed an inverse power law between 3 and ca. 60 or 70p. The exponent was not determined unequivocally, but it has a value between 3 and 4.5. Above 70fi the size frequency curve drops off rather sharply as a result of particles having been lost from the cloud by sedimentation. The effect of sedimentation was investigated theoretically. Correction factors to the size distribution were calculated as a function of particle size, and theoretical cutoff sizes were determined. The correction to the size frequency curve is less than 5% below about 70but it rises rather rapidly above this size. The corrections allow the correlation of the experimentally determined size distributions of the samples with those of the clouds, assuming cloud homogeneity. 

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