Nanoscale particles, materials systems

There is great interest in the electrical and optical properties of materials confined within small particles known as nanoparticles. These are materials made up of clusters (of atoms or molecules) that are small enough to have material properties very different from the bulk. Most of the atoms or molecules are near the surface and have different environments from those in the interior—indeed, the properties vary with the nanoparticle s actual size. These are key players in what is hoped to be the nanoscience revolution. There is still very active work to learn how to make nanoscale particles of defined size and composition, to measure their properties, and to understand how their special properties depend on particle size. One vision of this revolution includes the possibility of making tiny machines that can imitate many of the processes we see in single-cell organisms, that possess much of the information content of biological systems, and that have the ability to form tiny computer components and enable the design of much faster computers. However, like truisms of the past, nanoparticles are such an unknown area of chemical materials that predictions of their possible uses will evolve and expand rapidly in the future. 

The advent of a new class of materials systems based on nanoscale particles dispersed or suspended in carrier and/or binders has captured the attention of the microelectronics technical community. These materials provide the opportunity to use inexpensive solution processing equipment versus expensive vacuum deposition equipment commonly used in the microelectronics manufacturing industry. Experts in the microelectronics industry have suggested that over the course of the next live years, the industry will experience a paradigm shift in manufacturing and, more importantly, will enjoy revenue streams created from never-before-seen products based on printed electronics. 

Another possibility mentioned above is the addition of nanoscale particles to a liquid matrix system where the nanoscale particles are grown outside of the system. Experiments have been carried out with boehmite in a matrix derived from Si(OR)4/Al(OR)3 and glycidyloxypropyl triethoxy silane (GTPS) [22]. Even the addition of 5 % by volume of y-alumina or boehmite leads to systems which show a remarkably increased scratch-resistance compared to the unfilled material. The optical transparency is not influenced if the particle size of the boehmite is below 20 or 30 nm. In Fig. 21 the scratch resistance by the Vickers diamond test of the unfilled system is compared to the filled system and, as one can see, the scratch resistance is increased remarkably. 

We find that a layer model analysis can adequately describe the Pt NMR spectrum of nanoscale electrode materials. The shifts of the surface and sub-surface peaks of Pt NMR spectra correlate well with the electronegativity of various adsorbates, while the Knight shift of the adsorbate varies linearly with the f-LDOS of the clean metal surface. The Pt NMR response of Pt atoms from the innermost layers of the nanoparticles does not show any influence of the adsorbate present on the surface. This provides experimental evidence, which extends the applicability of the Friedel-Heine invariance theorem to the case of metal nanoparticles. Further, a spatially-resolved oscillation in the s-like E( -LDOS was observed via Pt NMR of a carbon-supported Pt catalyst sample. The data indicate that much of the observed broadening of the bulk-like peak in Pt NMR spectra of such systems can be attributed to spatial variations of the A( f). The oscillatory variation in A(A) beyond 0.4 nm indicates that the influence of the metal surface goes at least three layers inside the particles, in contrast to the predictions based on the Tellium model. 

The pol5mier nanocomposite field has been studied heavily in the past decade. However, polymier nanocomposite technology has been around for quite some time in the form of latex paints, carbon-black filled tires, and other pol5mier systems filled with nanoscale particles. However, the nanoscale interface nature of these materials was not truly understood and elucidated until recently [2 7]. Today, there are excellent works that cover the entire field of polymer nanocomposite research, including applications, with a wide range of nanofillers such as layered silicates (clays), carbon nanotubes/nanofibers, colloidal oxides, double-layered hydroxides, quantum dots, nanocrystalline metals, and so on. The majority of the research conducted to date has been with organically treated, layered silicates or organoclays. 

It has ako become apparent that nanoscale particles and clusters, especially those with principal size dimensions of less than 10 nm, are more active catalyti-cally than are larger sizes of the same materials. This is leading to the development of a new generation of catalyst systems of higher performance. 

Once the particle sizes are diminished down to the nanoscale (< 100 nm), the wear performance of these nanocomposites differs significantly from that of micron particle-filled systems. Polymers filled with nanoparticles are recently under discussion because of some excellent properties they have shown under various testing conditions. Some results were achieved in various studies, suggesting that this method is also promising for new processing routes of wear resistant materials. For instance, Xue et al. found that various kinds of SiC particles, i.e., nano, micron and whisker, could reduce the friction and wear when incorporated into a PEEK matrix at a constant filler content, e.g., 10 wt.% ( 4 vol.%). However, nanoparticles resulted in the most effective reduction. Nanoparticles were observed to be of help to the formation of a thin, uniform, and tenacious transfer film, which led to this improvement. The variation of Zr02 nanoparticles from 10 to 100 nm was conducted by Wang et al. The results showed a similar trend as most of the micron particles, i.e., the smaller the particles, the better was the wear resistance of the composites. 

Although SEMs or ESEMs are very powerful in imaging nanoscale materials or particles, caution should be taken to avoid electron beam damage to specimen. This is particularly important when a nanomanipulation system with a force measurement device is to be used to characterise the mechanical properties of particles. Ren et al. (2007, 2008) identified that such damage depended on the electron dose and exposure time, as well as the type of materials under test, and it is extremely important to find a time window in which the damage is negligible to obtain reliable mechanical property data. 

The hydrogen-bond mediated self-assembly of nanoparticles and polymers provides a versatile and effective method to control interparticle distances, assembly shapes, sizes, and anisotropic ordering of the resultant nanocomposites. This approach presents the bottom-up strategy to fabricate nanomaterials from molecular building blocks, which have great potential for assembling and integrating nanoscale materials and particles into advanced structures, systems, and devices. 

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