Nonspecific Properties of Materials

The pyrotechnist s relation to the pyrochemically active materials in a formula depends on the specific purpose For the production to prescribed specifications of a standardized item, he is mainly concerned with obtaining the materials promptly From commercial sources and in the verification of compliance of the ddivered materials with the specifications, In a developmental effort the emphasis is on the experimental study of different grades of known and proven materials in varying proportions. Final y, in research as well as in development of new types of devices, he may also consider substances formerly not regarded as useful for pyrotechnics. 

Most chemicals, such as metal powders, other elements, and metal oxides, are far from being of highest purity in the form in which they are offered in the trade for pyrotechnic purposes. Such materials are mostly well suited though, exceptionally, some impurities in a commercial product can be detrimental. 

Impurities are somewhat more important in the water-soluble salts such as nitrates, chlorates, and perchlorates. Commercial potassium salts are generally of adequately high purity because of the ease with which they can be recrystallized, being little soluble in cold water and much more soluble in hot, and the same applies to barium nitrate. This is fortunate for the production of colored H ts where even traces of sodium, a common impurity, would influence adversely the creation of a blue, green, or red effect. Sodium nitrate is less hygroscopic (to a point) the purer it is. Obviously the manufacturer must decide whether his product can tolerate the somewhat more hygroscopic grade or if he has to use the more expensive purer material. 

No property of the ingredients of a pyrotechnic formula is more critical than what is loosely called particle size, and none is at times more elusive and baffling. Our discussion will concentrate on metal powders, these being literally the focal points of most compositions (the Latin word focus means hearth or fireplace). Particle size or. 

If metal powders could be bought as one buys ball-bearings—i.e. as truly spherical entities all of the same diameter and of a true smooth surface area, approaching the geometrical surface as much as is practically possible—the problem of reproducibility would barely exist (Perhaps such a powder would be unignitible, but that is another problem ) 

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The precise stereogeometry of molecules is important in determining the physical properties of a material and is critical in determining the biological properties of materials. Most synthetic and nonspecific natural polymers are a mix of stereoshapes with numerous stereocenters along the polymer chain. For polypropylene, every other backbone carbon is most likely a stereocenter. Even polyethylene has stereochemical sites wherever there is branching. The imprecise structures of most natural nonspecific polymers such as the polyisoprenes and polysaccharides have stereocenters at each branch. 

Preparation of Solid Phase Antibody. There are many chemical and physical methods by which antibodies may be linked to different solid phase materials. Unfortunately relatively little work has been carried out to investigate systematically the properties of the different methods and materials. The main desirable characteristics are (a) convenience of handling and standardization both in preparation and in utilization b) adequate amount of antibody bound and stability of the preparation both in terms of the binding to solid phase and on storage (c) a low degree of nonspecific binding on the subsequent addition of antigen and labeled antibody. 

The biomimetic membranes represent a special group of carrier membranes. They are artificial membranes based on biomembrane mimicking, i.e., imitation of the essential features bio membranes use for separation. Nitrocellulose filters impregnated with fatty acids, their esters, and other lipid-like substances may be used— in other words, an imitation of many nonspecific barrier properties of biomembranes. The transport of gas through these membranes will essentially be according to facilitated transport (see Section 4.2). Biomimetic membranes for CO2 capture will transport the gas as HCO3. Development of these materials may be expected for selected applications. 

Microchip substrate is open to a variety of materials. Silicon wafer is a good material to build up microstructures if fabrication facilities are available. Glass has good chemical and optical properties, and some polymers are cost effective for mass production. The surface treatment of the microchannel is critically important for all materials. This is because of the nonspecific adsorption of the analytes and antibodies to the channel wall that will result in considerable analytical error. It is very important to modify the surface with some blocking reagents or other materials to prevent protein adsorption before experiments. Therefore, we must choose a material of which, surface chemistry is well understood. 

It is well described that materials in contact with biofluids are irmnediately coated with proteins. Protein adsorption is influenced by the underlying substrate surface properties including surface chemistry, charge, and free energy. After cell adhesion on top of this primary protein layer, the formation of secondary protein layers can take place due to nonspecific adsorption of ceU-secreted proteins (Fig. 4.27). 

WulflF sees the polydispersity of the imprinted receptor sites, nonspecific binding problems and the poor mass transfer properties of typical imprinted materials as key problems. He has recently published work on imprinting using strong noncovalent interactions to achieve near-stoichiometric association of templates and functional monomers in an attempt to improve the homogeneity of receptor sites and minimize the fraction of functional monomers dispersed non-specifically in the polymer structure. Continuation of this work, along with related work from other groups, will no doubt lead to further advances in this area. 

The unique properties of zeohtes for application in ion exchange, sorption, and catalysis are related to the fact that (1) the diameters of the micropores are in the range of the kinetic diameters of potential reactants (see Fig. 1) and (2) the surface functional groups having acid-base or redox properties are an integral part of the crystal structure. Thus, the nonspecific interactions between these materials and the reactant molecules are typically very strong and, therefore, the sorption properties markedly influence the catalytic activity. 

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