Microscope sizing optical

The optical microscope is a valuable tool in the laboratory and has numerous applications in most industries. Depending on the type of data that is required to solve a particular problem, optical microscopy can provide information on particle size, particle morphology, color, appearance, birefringence, etc. There are many accessories and techniques for optical microscopy that may be employed for the characterization of the physical properties of materials and the identification of unknowns, etc. Utilization of a hot-stage accessory on the microscope for the characterization of materials, including pharmaceutical solids (drug substances, excipients, formulations, etc.), can be extremely valuable. As with any instrument, there are many experimental conditions and techniques for the hot-stage microscope that may be used to collect different types of data. Often, various microscope objectives, optical filters, ramp rates, immersion media, sample preparation techniques, microchemical tests, fusion methods, etc., can be utilized. 

Before the application of the small-angle X-ray diffraction and the electron optical methods of study to collagen, there existed a largely unfilled gap between the histological or microscopic size range and the molecular or chemical level. This intermediate region, which may be termed colloidal, was then represented by extensions of ordinary light optics beyond true resolution, i.e. by the indirect optical methods of ultramicroscopy and polarization optics. 

Figure 9.21. (a) Hexagonal structure of coalesced film (b) contact size measuremenl of latex pailicles (c) electron microscope and optical measuiements confinniitg /KR theory fot latex. 

Unlike other particle sizers, the microscope gives the operator a clear visual outline of each individual particle being measured. In addition, the material may be presented in its normal form, dry or in a liquid medium. Particles that are aggregated can be identified and will not be measured as a single entity. Problems associated with microscopic sizing lie not only in the tedious nature of the technique but also in the slide sample preparation, optical resolution, and operator bias. 

Visual inspection of microscopical structure is an invaluable tool for a deep knowledge of filters. This is why the visualizing techniques were very early used to characterize them. Nevertheless, as the developed filters included relevant structures with submicron sizes, optical microscopy was no longer useful to achieve a... 

One of the most important uses of specific surface determination is for the estimation of the particles size of finely divided solids the inverse relationship between these two properties has already been dealt with at some length. The adsorption method is particularly relevant to powders having particle sizes below about 1 pm, where methods based on the optical microscope are inapplicable. If, as is usually the case, the powder has a raiige of particle sizes, the specific surface will lead to a mean particle size directly, whereas in any microscopic method, whether optical or electron-optical, a large number of particles, constituting a representative sample, would have to be examined and the mean size then calculated. 

Most tests of the validity of the BET area have been carried out with finely divided solids, where independent evaluation of the surface area can be made from optical microscopic or, more often, electron microscopic observations of particle size, provided the size distribution is fairly narrow. As already explained (Section 1.10) the specific surface obtained in this way is related to the mean projected diameter through the equation... 

Physical testing appHcations and methods for fibrous materials are reviewed in the Hterature (101—103) and are generally appHcable to polyester fibers. Microscopic analyses by optical or scanning electron microscopy are useful for evaluating fiber parameters including size, shape, uniformity, and surface characteristics. Computerized image analysis is often used to quantify and evaluate these parameters for quaUty control. 

Particle Morphology, Size, and Distribution. Many fillers have morphological and optical characteristics that allow these materials to be identified microscopically with great accuracy, even in a single particle. Photomicrographs, descriptions, and other aids to particle identification can be found (1). 

Microscopic identification models ate similar to the CMB methods except that additional information is used to distinguish the source of the aerosol. Such chemical or morphological data include particle size and individual particle composition and are often obtained by electron or optical microscopy. 

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