Influential properties

The reinforcement of rubber by the presence of active fillers is a complex phenomenon that depends on the characteristics of the elastomer network and the properties of the fillers. The influential properties are the particle size, the morphology of particle aggregates, and the surface properties. The role of the geometrical characteristics of the tiller is well understood, whereas the significance of the surface properties is more difficult to analyze. This situation stems essentially from the lack of adequate methods to analyze the surface of such small particles and from the fact that fillers differ from each other and need to be considered individually. 

Occasionally in component design, transparency can be a very influential property. Total, glass-like clarity can only be found in amorphous thermoplastics. The most widely used of these are PC, PMMA, SAN (styrene... 

The above phenomena and descriptions indicate the importance of dust properties and characterisation. Current trends and experiences indicate the following major influential properties ... 

As we saw in Chapter 3, the founding text of modern materials science was Frederick Seitz s The Modern Theory of Solids (1940) an updated version of this, also very influential in its day, was Charles Wert and Robb Thomson s Physies of Solids (1964). Alan Cottrell s Theoretical Structural Metallurgy appeared in 1948 (see Chapter 5) although devoted to metals, this book was in many ways a true precursor of materials science texts. Richard Weiss brought out Solid State Physics for Metallurgists in 1963. Several books such as Properties of Matter (1970), by Mendoza and Flowers, were on the borders of physics and materials science. Another key precursor book, still cited today, was Darken and Gurry s book. Physical Chemistry of Metals (1953), followed by Swalin s Thermodynamics of Solids. 

The surface of the substrate, the silicone/substrate interface, and the bulk properties of silicones all play significant and influential roles that affect practical adhesion and performance of the silicone. The design of silicone adhesives, sealants, coatings, encapsulants or any products where adhesion property is needed requires the development chemist to have a thorough understanding of both silicone chemistry and adhesion phenomena. 

The mechanical properties of ionomers can be appreciably altered by the manner in which the ionomer is prepared and treated prior to testing. Some of the factors that are influential are the degree of conversion (neutralization) from the acid form to the salt form, the nature of the thermal treatment or aging, the type of counterion that is introduced, the solvent that is used for preparation of thin films, and the presence and nature of any plasticizers or additives that may be present. In the scope of this chapter, it is not possible to provide a complete description of the influence of each of these variables on the wide variety of ionomers that are now commercially available or produced in the laboratory. Instead, one or more examples of the changes in properties that may be induced by each of the processing variables is presented and discussed. 

The problem-solving approach that ties the processing variables to products properties includes considering melt orientation, polymer degradation, free volume/molecular packing and relaxation, cooling stresses, and other such factors. The most influential of these four conditions is melt orientation, which can be related to molded-in stress or strain. 

While a number of introductory or comprehensive texts dealing with polymer chemistry were written, the most influential was probably Paul J. Flory s textbook "Principles of Polymer Chemistry", published in 1954. No prior knowledge of polymers was assumed with particular chapters directed at the beginner. It also contained much information useful to the experienced investigator. A wealth of experimental data was included to illustrate the applicability of the presented concepts and conclusions. Admittedly missing are topics related to the mechanical properties of polymers and to the application of polymers in industry - i.e. fabrication, synthesis, etc. Even so Flory s text is a landmark book in science. 

Niels Bohr was a physicist, not a chemist. I devote a chapter to his life because he was the scientist who explained why Mendeleev s periodic table had the properties it did. Widely known as a soccer player in his youth, Bohr became the most influential physicist of the first half of the twentieth century. His life, too, was touched by political events. A Jew living in occupied Denmark, Bohr had to flee the country to avoid arrest by the Nazis. In 1939 Bohr discovered a theory that explained nuclear fission, and suggested that uranium 235 could be used to make a bomb. Though he played only a minor role in the American atomic bomb project, Bohr was the first to ponder the political implications of the bomb. 

Nitrenium ions (or imidonium ions in the contemporaneous nomenclature) were described in a 1964 review of nitrene chemistry by Abramovitch and Davis. A later review by Lansbury in 1970 focused primarily on vinylidine nitrenium ions. Gassmann s ° 1970 review was particularly influential in that it described the application of detailed mechanistic methods to the question of the formation of nitrenium ions as discrete intermediates. McClelland" reviewed kinetic and lifetime properties of nitrenium ions, with a particular emphasis on those studied by laser flash photolysis (LFP). The role of singlet and triplet states in the reactions of nitrenium ions was reviewed in 1999. Photochemical routes to nitrenium ions were discussed in a 2000 review. Finally, a noteworthy review of arylnitrenium ion chemistry by Novak and Rajagopal " has recently appeared. 

Of the three general categories of transport processes, heat transport gets the most attention for several reasons. First, unlike momentum transfer, it occurs in both the liquid and solid states of a material. Second, it is important not only in the processing and production of materials, but in their application and use. Ultimately, the thermal properties of a material may be the most influential design parameters in selecting a material for a specific application. In the description of heat transport properties, let us limit ourselves to conduction as the primary means of transfer, while recognizing that for some processes, convection or radiation may play a more important role. Finally, we will limit the discussion here to theoretical and empirical correlations and trends in heat transport properties. Tabulated values of thermal conductivities for a variety of materials can be found in Appendix 5. 

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