Nanotechnology and polymer nanocomposites — страница 6

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associated excitement surrounding nanoscience and technology, affords unique opportunities to create these revolutionary material combinations. These new materials promise to enable the circumvention of classic material performance trade-offs by accessing new properties and exploiting unique synergisms between constituents that only occur when the length scale of the morphology and the critical length associated with the fundamental physics of a given property coincide. From a materials perspective, morphologies that exhibit nanoscopic features are necessary but far from sufficient – the key opportunities are afforded either when the physical size of the material’s constituents is engineered to coincide with the onset of nonbulk-like behavior, such as observed for the

size-dependent light emission of quantum dots (QDs), or when a structure-property relationship approaches a singularity or depends nonlinearly on aspects of the morphology, such as the internal interfacial area. Polymeric nanocomposites (PNCs) have been an area of intense industrial and academic research for the past 20 years. No matter the measure – articles, patents, or R&D funding – efforts in PNCs have been exponentially growing worldwide over the last ten years. PNCs represent a radical alternative to conventional filled polymers or polymer blends – a staple of the modern plastics industry. The reinforcement of polymers using fillers, whether inorganic or organic, is common in the production of modern plastics. Polymeric nanocomposites or polymer nanostructured

materials represent a radical alternative to conventional-filled polymers or polymer blends. In contrast to the conventional systems where the reinforcement is on the order of microns, discrete constituents on the order of a few nanometers (~10,000 times finer than a human hair) exemplify PNCs. Uniform dispersion of these nanoscopically sized filler particles (or nanoelements) produces ultra-large interfacial area per volume between the nanoelement and host polymer. This immense internal interfacial area and the nanoscopic dimensions between nanoelements fundamentally differentiate PNCs from traditional composites and filled plastics. Thus, new combinations of properties derived from the nanoscale structure of PNCs provide opportunities to circumvent traditional performance

trade-offs associated with conventional reinforced plastics, epitomizing the promise of nano-engineered materials. A literature search provides many examples of PNCs, demonstrating substantial improvements in mechanical and physical properties. However, the nanocomposite properties discussed are generally compared to unfilled and conventional-filled polymers, but are not compared to continuous fiber reinforced composites. Although PNCs may provide enhanced, multifunctional matrix resins, they should not be considered a potential one-for-one replacement for current state-of-the-art carbon-fiber reinforced composites. From both a commercial and military perspective, the value of PNC technology is not based solely on mechanical enhancements of the neat resin. Rather, it comes from

providing value-added properties not present in the neat resin, without sacrificing the inherent processibility and mechanical properties of the resin. Traditionally, blend or composite attempts at multifunctional materials require a trade-off between desired performance, mechanical properties, cost, and processibility. Considering the number of potential nanoelements, polymeric resins, and applications, the field of PNCs is immense. Development of multicomponent materials, whether microscale or nanoscale, must simultaneously balance four interdependent areas: constituent-selection, fabrication, processing, and performance. This is still in its infancy for PNCs, but ultimately scientists will develop many perspectives dictated by the final application of the PNC. Researchers

developed two main PNC fabrication methodologies: in-situ routes and exfoliation. Currently, researchers in industry, government, and academia worldwide are heavily investigating exfoliation of layered silicates, carbon nanofibers/nanotube-polymer nanocomposites, and high-performance resin PNCs. This picture shows the complex arrangement of the copper conductors in a computer chip. The smallest wires are less than a millionth of a meter in diameter. Copper is starting to replace aluminum in computer chips because it conducts electricity better (better performance!) and has a higher melting temperature (lasts longer!). It took many years of materials science research worldwide to figure out how to produce chips with copper conductors. Notwithstanding the considerable advances in