Polymer Nanocomposites with Particle and Carbon Nanotube Fillers
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Polymer nanocomposites are composites with a polymer matrix and a filler with at least one dimension less than 100 nm. The fillers can be plate-like (clays), high aspect ratio nanotubes, and lower aspect ratio or equiaxed nanoparticles. While some nanofilled composites (carbon black and fumed silica-filled polymers) have been used for over a century, in recent years the dedicated research and development of nanofilled polymers has greatly increased. This is due to our increased ability to synthesize and manipulate a broad range of nanofillers and significant investment by government and industry in this field.
Current interest in nanocomposites has been generated and maintained because nanoparticle and carbon nanotube-filled polymers exhibit unique combinations of properties not achievable with traditional composites. For example, the inclusion of equiaxed nanoparticles in thermoplastics, and particularly semicrystalline thermoplastics, increases the yield stress, the tensile strength, and Young's modulus compared to pure polymer. Other examples include scratch-resistant transparent amorphous thermoplastic coatings. These combinations of properties can be achieved because of the small size of the fillers, the large surface area the fillers provide, and in many cases the unique properties of the fillers themselves. As will be shown, in many cases these large changes in the material properties require small to modest nanofiller loadings. Unlike traditional micron-filled composites, these novel fillers often alter the properties of the entire polymer matrix while, at the same time, imparting new functionality because of their chemical composition and nanoscale size.
This article will give a general introduction to polymer nanocomposites and address what is unique to nanofillers compared to traditional micron-scale fillers. The second section will briefly address nanofiller surface modification and the third will provide specific examples of mechanical, electrical, and optical properties in nanoparticle-filled polymers. The last section provides a detailed description of the mechanical properties of nanotube-filled polymers and a brief description of some electrical and optical properties that have been reported.