Biological colloids

Applications of Dielectrophoresis Over the past 20 years the use of DEP has grown rapidly to a point at which it is in use for biological, colloidal, and mineral materials studies and handfing. The effects of nonuniform elec tric fields are used for handling particulate matter far more often than is usually recognized. This includes the... 

Biologicals, colloids and macromolecules Membrane-impermeable gases and vapors Virtually all suspended and dissolved materials Dissolved and suspended materials with molecular weight >1,000 All non-ionic and macromolecular species ... 

Similar calculations can be given for oblate ellipsoids, but the errors will be larger than those for the prolate ellipsoids if an incorrect p value is used. In any case the flattened disc model rarely finds use in biological colloids. The same uncertainty has also been found in the use of Eq. (29b) and it will therefore not be discussed further. 

Towards the end of the chapter we point out the biological importance of an understanding of colloid chemistry and several examples of biological importance are covered. Pharmaceutical and biological colloids are often very... 

The influence of electrical charges on surfaces is very important to their physical chemistry. The Coulombic interaction between charged colloids is responsible for a myriad of behaviors from the formation of opals to the stability of biological cells. Although this is a broad subject involving both practical application and fundamental physics and chemistry, we must limit our discussion to those areas having direct implications for surface science. 

G. J. T. Tiddy, in Modem Treruis of Colloid Science in Chemistry and Biology, H. Eicke, ed., Birkhauser-Verlag, Basel, 1985 Phys. Rep., 57, 1 (1980). 

Evans D F and Wennerstrom H 1994 The Colloidal Domain—Where Physics, Chemistry, Biology, and Technology Meet (New York VCH) pp 12-16... 

J. N. Israelachvih, Intermolecular and Suface Forces, With Applications to Colloidal and Biological Systems, Academic Press, Inc., San Diego, 1985. 

Electroultrafiltration (EUF) combines forced-flow electrophoresis (see Electroseparations,electrophoresis) with ultrafiltration to control or eliminate the gel-polarization layer (45—47). Suspended colloidal particles have electrophoretic mobilities measured by a zeta potential (see Colloids Elotation). Most naturally occurring suspensoids (eg, clay, PVC latex, and biological systems), emulsions, and protein solutes are negatively charged. Placing an electric field across an ultrafiltration membrane faciUtates transport of retained species away from the membrane surface. Thus, the retention of partially rejected solutes can be dramatically improved (see Electrodialysis). 

T. Alan Hatton, Ph.D., Ralph Landau Professor and Director of the David H. Koch School of Chemical Engineering Practice, Massachusetts Institute of Technology Founding Fellow, American Institute of Medical and Biological Engineering Member, American Institute of Chemical Engineers, American Chemical Society, International Association of Colloid and Interface Scientists, American Association for the Advancement of Science, Neutron Scattering Society of America (Section 22, Alternative Separation Processes)... 

The numerous separations reported in the literature include surfactants, inorganic ions, enzymes, other proteins, other organics, biological cells, and various other particles and substances. The scale of the systems ranges from the simple Grits test for the presence of surfactants in water, which has been shown to operate by virtue of transient foam fractionation [Lemlich, J. Colloid Interface Sci., 37, 497 (1971)], to the natural adsubble processes that occur on a grand scale in the ocean [Wallace and Duce, Deep Sea Res., 25, 827 (1978)]. For further information see the reviews cited earlier. 

A lot of natural as well as technological objects of analytical control are colloidal systems, i.e. human blood, biological liquids, sol and suspension forming in different technological processes (ore-dressing, electrochemical deposition, catalysis and other), food, paint-and-lacquer materials, sewage water and other. 

The broader field of colloid science continues to attract overviews, the most recent being a book entitled The Colloidal Domain, Where Physics, Chemistry am Biology Meet (Evans and Wennestrdm 1999). 

Evans, D.F. and Wenneslrdm, H. (1999) The Colloidal Domain, Where Physics, Chemistry and Biology Meet (Wiley-VCH, Weinheim). 

Biological wastewater treatment processes also affect solids characteristics and hence solids separation. Activated sludge solids have been found to have a distinct bimodal distribution with one mode in the supracolloidal to settleable range and another near the border between the colloidal and supracolloidal fractions. The concentrations and size limits in each range are affected by conditions in the... 

Typically RO systems are preceded by pretreatment units to remove suspended solids/colloidal matter and add chemicals that control biological growth and reduce scaling. Membranes are typically made of synthetic polymers coated on a backing (skin). Examples of membrane materials include polyamides, cellulose acetate and sulfonated polysulfone. 

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