Extreme Microstructures

Nano-structures comments on an example of extreme microstructure In a chapter entitled Materials in Extreme States , Cahn (2001) dedicated several comments to the extreme microstructures and summed up principles and technology of nano-structured materials. Historical remarks were cited starting from the early recognition that working at the nano-scale is truly different from traditional material science. The chemical behaviour and electronic structure change when dimensions are comparable to the length scale of electronic wave functions. Quantum effects do become important at this scale, as predicted by Lifshitz and Kosevich (1953). As for their nomenclature, notice that a piece of semiconductor which is very small in one, two- or three-dimensions, that is a confined structure, is called a quantum well, a quantum wire or a quantum dot, respectively. 

The use of NMR spectroscopy to characterize copolymer microstructure takes advantage of this last ability to discern environmental effects which extend over the length of several repeat units. This capability is extremely valuable in analyzing the stereoregularity of a polymer, and we shall have more to say about it in that context in Sec. 7.11. 

The microstructure of commercial varistors is extremely complex, and commercial preparations also contain other dopants, mainly oxides of cobalt, manganese, chromium, and antimony, that are used to fine tune the varistor characteristics. The transition-metal dopants are chemically similar to Zn2+ and mainly form substitutional defects within the ZnO grains, such as CoZn, that modify the n-type behavior of the grain interior. (See also Chapter 8 for further discussion of the electronic... 

Very few of the references in Tables 1-3 attempt any quantitative modelling of their NMR data in terms of cell microstructure or composition. Such models would be extremely useful in choosing the optimum acquisition pulse sequences and for rationalising differences between sample batches, varieties and the effects of harvesting times and storage conditions. The Numerical Cell Model referred to earlier is a first step in this direction but more realistic cell morphologies could be tackled with finite element and Monte Carlo numerical methods. 

Another technological breakthrough in optical hber technology, however, allows one to upgrade established 100 fs-class laser systems for broadband applications and even surpass the bandwidth of dedicated short-pulse Ti sapphire lasers. Key to this is the use of novel microstructured optical hbers, which are designed to exhibit extremely high optical nonlinearities. If nanojoule femtosecond laser pulses are launched into such a hber, the combination of different nonlinear optical processes leads to the creation of new frequency components. Therefore, the laser bandwidth can be increased dramatically by orders of magnitude. 

The microstructure and imperfection content of coatings produced by atomistic deposition processes can be varied over a very wide range to produce structures and properties similar to or totally different from bulk processed materials. In the latter case, the deposited materials may have high intrinsic stress, high point-defect concentration, extremely fine grain size, oriented microstructure, metastable phases, incorporated impurities, and macro-and microporosity. All of these may affect the physical, chemical, and mechanical properties of the coating. 

Interfacial structure is known to be different from bulk structure, and in polymers filled with nanofillers possessing extremely high specific surface areas, most of the polymers is present near the interface, in spite of the small weight fraction of filler. This is one of the reasons why the nature of the reinforcement is different in nanocomposites and is manifested even at very low filler loadings (<10 wt%). Crucial parameters in determining the effect of fillers on the properties of composites are filler size, shape, aspect ratio, and filler-matrix interactions [2-5]. In the case of nanocomposites, the properties of the material are more tied to the interface. Thus, the control and manipulation of microstructural evolution is essential for the growth of a strong polymer-filler interface in such nanocomposites. 

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