Physics of microparticles

This review of the chemistry and physics of microparticles and their characterization is by no means comprehensive, for the very large range of masses that can be studied with the electrodynamic balance makes it possible to explore the spectroscopy of atomic ions. This field is a large one, and Nobel laureates Hans Dehmelt and Wolfgang Paul have labored long in that fruitful scientific garden. The application of particle levitation to atmospheric aerosols, to studies of Knudsen aerosol phenomena, and to heat and mass transfer in the free-molecule regime would require as much space as this survey. 

Wagner, P. E., in Topics in Current Physics Vol. 29 Aerosol Microphysics II Chemical Physics of Microparticles. W. H. Marlow, ed., Springer-Verlag, Berlin, 1982. 

B. Berne In Aerosol Micro-physics II Chemical Physics of Microparticles ed. by W.H. Marlow, Topics in Current Physics (Springer, Berlin, Heidelberg, New York, in preparation... 

Binders. To create needed physical strength in catalysts, materials called binders are added (51) they bond the catalyst. A common binder material is a clay mineral such as kaolinite. The clay is added to the mixture of microparticles as they are formed into the desired particle shape, for example, by extmsion. Then the support is heated to remove water and possibly burnout material and then subjected to a high temperature, possibly 1500°C, to cause vitrification of the clay this is a conversion of the clay into a glasslike form that spreads over the microparticles of the support and binds them together. 

The production of fine particles that are either desirable (polymer colloids, ceramic precursors, etc.) or undesirable (soot, condensed matter from stack gases, etc.) involves chemical reactions, transport processes, thermodynamics, and physical processes of concern to the chemical engineer. The optimization and control of such processes and the assurance of the quality of the product requires an understanding of the fundamentals of microparticles. 

There has been much less work done in the area of microparticle chemistry compared with studies of the physics of small particles, but this is an area of considerable interest to chemical engineers. The work of Matijevic and his colleagues on polymeric aerosols and of Rubel and Gentry on gas/droplet reactions was mentioned earlier, as was the application of fluorophores by Ward et al. (1987) to explore microparticle polymerization. The recent development of microparticle spectroscopic techniques makes it possible to follow chemical reactions between a reactive gas and a microparticle. 

A type I process that considers the motion of microparticles occurring with a velodty Vj = v this velocity is induced by the surrounding flowing fluid (physically this type of process corresponds to the non-deposition of the microparticle) ... 

Many other tests could have been included to demonstrate the value of in vitro tests in quality control. Some, such as multistage impingers for aerosols, can be predictive of in vivo behaviour, or at least give an assurance of consistency of effect. An interesting test system for evaluating inhaled nasal delivery systems (Fig. 12.18) combines a physical device with cultured cells so that the interaction of microparticles with living cells can be studied directly. As new delivery systems appear, new tests will be required - as will ingenuity. 

Domenech, A., Domenech, M.T., and Vazquez, M.L. 2006c. Dehydroindigo A new piece into the Maya blue puzzle from the voltammetry of microparticles approach. Journal of Physical Chemistry B 110, 6027-6039. 

H.M. Hertz, Standing-wave acoustic trap for nonintrusive positioning of microparticles, Journal of Applied Physics, 78(8), 4845 849 (1995). 

Poly-L-Lactic acid is a physical adjunct that is an injectable implant of microparticles of poly-L-lactic acid. It is indicated in restoration and/or correction of signs of facial fat loss (lipoatrophy) in people with HIV. 

A microparticle is defined as a physical object whose wave properties can be registered. This class includes elementary particles, atomic nuclei, atoms (atomic ions), molecules (molecular ions) and more complex assemblies (like clusters and macromolecules). Some properties of microparticles belong to the universal physical constants (energy, mass, linear momentum, angular momentum, electric charge, magnetic moment) some, on the contrary, are exclusively specific for microparticles (spin, parity, life-time). Macroscopic state properties (such as temperature, pressure, volume, entropy, etc.) are irrelevant for a single microparticle. 

An alternative to dielectrophoretic or magnetic force manipulation of microparticles in suspension is the use of acoustic standing wave forces, which also have served as the basis for particle and cell manipulation in microfluidic devices. Historical work by Kundt demonstrated early on the ability to move cork particles in a standing wave pattern. The fundamental acousto-physical principles have been well researched and described in the literature by King and Gorkov. ... 

Another complication is the possibility of mass-transfer limitations on the reaction rate. And, because the polymer layer grows, mass transfer resistance will increase during a heterogeneous polymerization it is quite possible that the polymerization will start out reaction-limited and change to mass transfer-limited as the conversion increases. To polymerize, monomer must first diffuse from the bulk fluid surrounding the macroparticles, where its concentration is [M ], to the catalytic surface within the microparticles, where its concentration is [MJ. Where the inherent rate of reaction on the catalytic surface and/or the resistance to diffusion are high, the overall reaction rate can be determined by the physics of diffusion rather than the chemistry of the reaction. 

Vijayaraghavan,M., Stolnik,S.,Howdle, S. M.,Ilium,L. (2013). Suitability of polymer materials for production of pulmonary microparticles using a PGSS supercritical fluid technique Preparation of microparticles using PEG, fatty acids and physical or chemicals blends of PEG and fatty acids, Int J. Pharm., 441,580-588. 

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