ABSTRACT
Acknowledgment...............................................................................................363 References .........................................................................................................363
The term “nanocomposites” was first coined by Roy et al. sometime during the period 1982 to 1983 to describe the major conceptual redirection of the sol-gel process, that is, using the solution sol-gel (SSG) process to create maximally heterogeneous instead of homogeneous materials.l-4 Di-and multiphasic nanoheterogeneous sol-gel materials were prepared and documented in 1984.1-4 Nanocomposites should be clearly differentiated from “nanocrystalline” and “nanophase” materials, which refer to single phases in the nanometer range. “Nanocomposites” refers to composites of more than 1 Gibbsian solid phase where at least one dimension is in the nanometer range and typically all solid phases are in the 1 to 100 nm range. The solid phases can be amorphous, semicrystalline, or crystalline, or combinations thereof. They can be inorganic, organic, or both, and essentially of any composition. The “nanocomposite” theme has now been widely and accurately copied and used worldwide. Although the term “nanocomposites” was coined only recently, nanocomposites are pervasive throughout biological systems (e.g., plants and bones). Only very few man-made materials, such as intercalation compounds (e.g., graphite intercalation compounds, pillared clays, and clay-organic complexes) and entrapment-type compounds (e.g., zeolite-organic complexes) have dealt with this size of material. In the biological world, plants form nanocomposites with the accumulation of significant amounts of inorganic components such as silicon, calcium, aluminum, etc. at the tissue and cellular level to deal with the mechanical and biophysical demands of their survival. In the animal world, bones, teeth, and shells consist of nanocomposites of inorganic and organic materials to achieve several key properties. The objective of this chapter, however, is to review the work on manmade nanocomposite materials and to identify areas where further developments are likely to occur.
