In nanochemistry, the rules of bonding are extended from atoms and molecules to larger objects having the dimension of from 1 to 100 nanometers, where one nanometer is one-billionth of a meter. In this regime, new chemical and physical properties appear that depend on the size and shape of the particles. Nanochemistry undertakes the synthesis of precisely defined nanoparticles to achieve novel materials for specific applications in such fields as advanced catalysis, ultrathin films and membranes (separation and adsorption), storage devices, and optical and electronic devices. The nanometer regime is of particular interest because it is this region where phenomena associated with atomic and molecular interactions begin to be strongly influenced by the macroscopic properties of materials.
In mechanochemistry, individual chemical reactions at the molecular or atomic level are achieved by pressing the reactants together to overcome the normal reaction barriers. This requires positioning of the reactants on a nanometer scale to precisely bring the reactants together.
The fabrication of thin metallic wires, or nanowires, is a critical technology for communications technology. Methods that produce wires 20 times thinner, longer, and better-defined than conventional ones have been based on nanotechnology.
In gas phase condensation, the vapor evolved from an appropriate precursor undergoes a reaction that produces nanometer-sized particles.Indiumtinoxide particles made by this method are conductive, and can be processed to form transparent thin films that are antistatic. Other particles containing yttria and some lanthanides are phosphors that be processed to form light-emitting devices.
Nanostructured chip devices prepared from nanoscale materials (including complex oxides, carbides, borides and nitrides) have been successfully mass produced in kilogram quantities.
In the field of biology, biochemists have been studying vesicles, the small membrane sacs found within cells. Vesicles transport important molecules from cell to cell to keep cells functioning properly. Because vesicles are too small (from tens of nanometers to a few micrometers) to study by traditional chemical analysis, nanochemistry techniques have been employed to study these structures.
Surface scientists have been able to exploit atomic self-organization processes for the controlled fabrication of nanostructures at surfaces having well defined size and shape. This approach is based on a detailed understanding of the microscopic pathways of diffusion, nucleation and aggregation, processes governed by activation barriers for migrating atoms. The knowledge of the energetic hierarchy of the participating atomic diffusion events allows one to synthesize nanostructures of a desired size, dimension, and shape in large quantities by exploiting the laws of nature.
In nanocomposites, one of the constituent phases has dimensions—length, width, or thickness, in the nanometer range. Because the building blocks of the nanocomposite have the dimensions of nanometers, they have enormous surface areas and large interfaces with other phases. The properties of the nanocomposite result from interactions at these interfaces. In conventional composites where the building blocks have dimensions on the order of microns (one-millionth of a meter), there is less interfacial contact between phases, and consequently less effect by the interfaces on properties of the composite.
One naturally-occurring nanocomposite is bone. Bone consists to a large extent of nanoscale, platelike crystals of hydroxyapatite, Ca10(PO4)6(O H)2 dispersed in a matrix of collagen fibers. Conventional attempts to synthesize hydroxyapatite for artificial bone or bone implant materials have been fraught with difficulties, but scientists have found that these problems can be largely overcome if hydroxapatite is synthesized as a nanostructured material.
In the field of catalysis, chemists have been searching for catalysts that are stable at high temperatures. The complex oxide barium hexaaluminate (BHA), or BaO6Al2 O3, has been of interest it retains its catalytic activity at high temperatures. But conventional methods to synthesize BHA tend to reduce the material's surface area, and hence the activity. But when nanoparticles of BHA are prepared, a final grain size of 30 nanometers is achieved, and a large surface area and catalytic activity are achieved.
In organic/inorganic nanocomposites, a nanoscale inorganic filler is typically dispersed in an organic polymer matrix. The filler carries the load, and its large surface area in contact with the matrix reduces the mobility of the polymer chains.Nylon nanocomposites containing small amounts of clay that are capable of withstanding high temperature environments have been fashioned into automobile air intake covers.
Chemists have also been looking at carbon nanotubes (honeycomb graphite lattices rolled into cylinders having nanoscale thicknesses) as fillers in nanocomposites. The nanotubes, by virtual of their electrical conductivity, make the composite conductive as well. Nanotubes have been found by experiment to be stiffer than carbon fibers (which are thicker than 1 micron), but less brittle. Thus, nanocomposites containing carbon nanotubes are able to withstand much greater deformations before breaking than carbon fiber composites.
Nanochemistry, which is actually a branch of solid-state materials chemistry, is an emerging discipline with a promising future, and, as a consequence, many of the techniques employed are still evolving.
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