Nanotechnology and polymer nanocomposites — страница 7

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exfoliated PNCs, scientists must still conduct substantial fundamental research to provide a basic understanding of these materials to enable full exploitation of their nano-engineering potential. Despite the large number of combinations of matrices and potential reinforcing nanoelements with different chemistry, size, shape, and properties, all PNCs share common features with regard to fabrication methodologies, processing, morphology characterization, and fundamental physics. Developing an understanding of the characteristics of this interphase region, its dependence on nanoelement surface chemistry, the relative arrangement of constituents and, ultimately, its relationship to the PNC properties, is a current research frontier in nanocomposites. Equally important is the

development of a general understanding of the morphology-property relationships for mechanical, barrier, and thermal response of these systems. This necessitates the determination of the critical length and temporal scale with which continuum description of a physical process must give way to mesoscopic and atomistic view of these nanoscale systems—a current challenge for computational materials science. A rapidly growing area of nano-engineered materials is PNCs, providing lighter weight alternatives to conventional-filled plastics with additional functionality associated with nanoscale-specific value-added properties. If the promise and excitement surrounding layered silicates and carbon nanotubes are any indication, the future of PNC technology is truly boundless. The

opportunities to extend PNC concepts to other nanoelements and polymer hosts are immense, opening the way to provide tailor-made materials that circumvent current limitations and enable future concepts. PNC Framework The initial question when beginning to examine polymer nanocomposites is: how are these materials different from classic filled polymers or traditional composites? As anticipated, there is no simple answer; rather ‘they are related, but bring new opportunities, perspectives, and issues.’ Whether tubes (e.g. single- and multi-walled carbon nanotubes, SWNT and MWNTs, respectively) or plates (e.g. exfoliated graphite, layered silicates), the nanoscopic dimensions and extreme aspect ratios inherent in these nanofillers result in six interrelated characteristics

distinguishing the resultant PNCs from classic filled systems: q Low percolation threshold (~0.1-2 vol%); q Particle-particle correlation (orientation and position) arising at low volume fractions (φ C < 0.001); q Large number density of particles per particle volume (106-108 particles/µm3); q Extensive interfacial area per volume of particles (103-104 m2/ml); q Short distances between particles (10-50 nm at φ ~1-8 vol%); and q Comparable size scales among the rigid nanoparticle inclusion, distance between particles, and the relaxation volume of polymer chains. Properties And Applications of PNC’S Advantages of Nanosized Additions Researches have revealed clearly the property advantages that nanomaterial additives can provide in comparison to both their

conventional filler counterparts and base polymer. Properties which have been shown to undergo substantial improvements include: ·         Mechanical properties e.g. strength, modulus and dimensional stability ·         Decreased permeability to gases, water and hydrocarbons ·         Thermal stability and heat distortion temperature ·         Flame retardancy and reduced smoke emissions ·         Chemical resistance ·         Surface appearance ·         Electrical conductivity

·         Optical clarity in comparison to conventionally filled polymers Disadvantages of Nanosized Additions To date one of the few disadvantages associated with nanoparticle incorporation has concerned toughness and impact performance. Some of the data presented has suggested that nanoclay modification of polymers such as polyamides, could reduce impact performance. Clearly this is an issue which would require consideration for applications where impact loading events are likely. In addition, further research will be necessary to, for example, develop a better understanding of formulation/structure/property relationships, better routes to platelet exfoliation and dispersion etc. Particle Loadings In addition it is important to recognise