Introducing Microstructure

The microstructure plays a pivotal role with respect to the chemical properties of a material. Accordingly, if one wishes to use atomistic models to explore the reactivity, then the microstructure must be captured within the atomistic model including the morphology and surfaces exposed, intrinsic and extrinsic point defects, dislocations and grain boundaries. In the following we use selected examples to describe how such features are introduced. 

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Embossing is another cheap technique for introducing microstructures into metal foils and is certainly particularly suitable for mass production (see Figure 10.11). 

All polymer molecules have unique features of one sort or another at the level of individual repeat units. Occasional head-to-head or tail-to-tail orientations, random branching, and the distinctiveness of chain ends are all examples of such details. In this chapter we shall focus attention on two other situations which introduce variation in structure into polymers at the level of the repeat unit the presence of two different monomers or the regulation of configuration of successive repeat units. In the former case copolymers are produced, and in the latter polymers with differences in tacticity. Although the products are quite different materials, their microstructure can be discussed in very similar terms. Hence it is convenient to discuss the two topics in the same chapter. 

And so, as you can see from the Contents list, the chapters are arranged in groups, with a group of chapters to describe each of the four classes of materials. In each group we first introduce the major families of materials that go to make up each materials class. We then outline the main microstructural features of the class, and show how to process or treat them to get the structures (really, in the end, the properties) that we want. Each group of chapters is illustrated by Case Studies designed to help you... 

J Electron microprobe analysis. The instrument which I shall introduce here is, in my view, the most important development in characterisation since the 1939-1945 War. It has completely transformed the study of microstructure in its compositional perspective. 

A quite different approach was introduced in the early 1980s [44-46], in which a dense solid electrode is fabricated which has a composite microstructure in which particles of the reactant phase are finely dispersed within a solid, electronically conducting matrix in which the electroactive species is also mobile. There is thus a large internal reactant/mixed-conductor matrix interfacial area. The electroactive species is transported through the solid matrix to this interfacial region, where it undergoes the chemical part of the electrode reaction. Since the matrix material is also an electronic conductor, it can also act as the electrode s current collector. The electrochemical part of the reaction takes place on the outer surface of the composite electrode. 

The present review shows how the microhardness technique can be used to elucidate the dependence of a variety of local deformational processes upon polymer texture and morphology. Microhardness is a rather elusive quantity, that is really a combination of other mechanical properties. It is most suitably defined in terms of the pyramid indentation test. Hardness is primarily taken as a measure of the irreversible deformation mechanisms which characterize a polymeric material, though it also involves elastic and time dependent effects which depend on microstructural details. In isotropic lamellar polymers a hardness depression from ideal values, due to the finite crystal thickness, occurs. The interlamellar non-crystalline layer introduces an additional weak component which contributes further to a lowering of the hardness value. Annealing effects and chemical etching are shown to produce, on the contrary, a significant hardening of the material. The prevalent mechanisms for plastic deformation are proposed. Anisotropy behaviour for several oriented materials is critically discussed. 

When the length scale approaches molecular dimensions, the inner spinning" of molecules will contribute to the lubrication performance. It should be borne in mind that it is not considered in the conventional theory of lubrication. The continuum fluid theories with microstructure were studied in the early 1960s by Stokes [22]. Two concepts were introduced couple stress and microstructure. The notion of couple stress stems from the assumption that the mechanical interaction between two parts of one body is composed of a force distribution and a moment distribution. And the microstructure is a kinematic one. The velocity field is no longer sufficient to determine the kinematic parameters the spin tensor and vorticity will appear. One simplified model of polar fluids is the micropolar theory, which assumes that the fluid particles are rigid and randomly ordered in viscous media. Thus, the viscous action, the effect of couple stress, and... 

The microheterogeneity coefficient was introduced only for the description of the microstructure of binary copolymers with symmetric units. At increased number of unit types and/or when account is taken of structural isomerism, the role of Km will be performed by other parameters analogous to it. A general strategy for the choice of these latter has been elaborated in detail [12], while their values have been measured via NMR spectroscopic techniques for a variety of polycondensation polymers [13]. 

In another approach, two cascaded microstructure-collapses on a photonic crystal fiber are intentionally introduced by C02 laser or electric arc heating31. In this way, the mismatch of core size along the fiber causes light coupling between the core and cladding modes. 

The fabrication procedure affects the product s microstructure including grain size, grain-boundary width, and porosity. In addition, different procedures introduce various amounts of impurities to the product. Therefore, the electrical conductivity and activation energy are affected by the fabrication procedure since, as mentioned above,... 

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