Nanomaterials are applications with morphological features smaller than a one tenth of a micrometre in at least one dimension. Despite the fact that there is no consensus upon the minimum or maximum size of nanomaterials, with some authors restricting their size to as low as to nm, a logical definition would situate the nanoscale between microscale . micrometre and atomicmolecular scale about . nanometers. See Figure Classification of nanostructured materials.In physics, a quantum plural quanta is an indivisible entity of a quantity that has the same units as the Planck constant and is related to both energy and momentum of elementary particles of matter called fermions and of photons and other bosons. The word comes from the Latin quantus, for how much. Behind this, one finds the fundamental notion that a physical property may be quantized, referred to as quantization. This means that the magnitude can take on only certain discrete numerical values, rather than any value, at least within a range. There is a related term of quantum number.
A photon is often referred to as a light quantum. The energy of an electron bound to an atom at rest is said to be quantized, which results in the stability of atoms, and of matter in general. But these terms can be a little misleading, because what is quantized is this Plancks constant quantity whose units can be viewed as either energy multiplied by time or momentum multiplied by distance.Usually referred to as quantum mechanics, it is regarded by virtually every professional physicist as the most fundamental framework we have for understanding and describing nature at the infinitesimal level, for the very practical reason that it works. It is in the nature of things, not a more or less arbitrary human preference.Quantum theory, the branch of physics which is based on quantization, began in when Max Planck published his theory explaining the emission spectrum of black bodies. In that paper Planck used the Natural system of units he invented the previous year. The consequences of the differences between classical and quantum mechanics quickly became obvious. But it was not until , by the work of Werner Heisenberg, Erwin Schrödinger, and others, that quantum mechanics became correctly formulated and understood mathematically. Despite tremendous experimental success, the philosophical interpretations of quantum theory are still widely debated.
FUNDAMENTAL CONCEPTS
An aspect of nanotechnology is the vastly increased ratio of surface area to volume present in many nanoscale materials which makes possible new quantum mechanical effects, for example the “quantum size effect” where the electronic properties of solids are altered with great reductions in particle size. This effect does not come into play by going from macro to micro dimensions. However, it becomes pronounced when the nanometer size range is reached. A certain number of physical properties also alter with the change from macroscopic systems. Novel mechanical properties of nanomaterials is a subject of nanomechanics research. Catalytic activities also reveal new behaviour in the interaction with biomaterials.Nanotechnology can be thought of as extensions of traditional disciplines towards the explicit consideration of these properties. Additionally, traditional disciplines can be reinterpreted as specific applications of nanotechnology. This dynamic reciprocation of ideas and concepts contributes to the modern understanding of the field. Broadly speaking, nanotechnology is the synthesis and application of ideas from science and engineering towards the understanding and production of novel materials and devices. These products generally make copious use of physical properties associated with small scales.
As mentioned above, materials reduced to the nanoscale can suddenly show very different properties compared to what they exhibit on a macroscale, enabling unique applications. For instance, opaque substances become transparent copper inert materials attain catalytic properties platinum stable materials turn combustible aluminum solids turn into liquids at room temperature gold insulators become conductors silicon. Materials such as gold, which is chemically inert at normal scales, can serve as a potent chemical catalyst at nanoscales. Much of the fascination with nanotechnology stems from these unique quantum and surface phenomena that matter exhibits at the nanoscale.Nanosize powder particles a few nanometres in diameter, also called nanoparticles are potentially important in ceramics, powder metallurgy, the achievement of uniform nanoporosity and similar applications. The strong tendency of small particles to form clumps agglomerates is a serious technological problem that impedes such applications. However, a number of dispersants such as ammonium citrate aqueous and imidazoline or oleyl alcohol nonaqueous are promising solutions as possible additives for deagglomeration.
SIZE CONCERNS
Another concern is that the volume of an object decreases as the third power of its linear dimensions, but the surface area only decreases as its second power. This somewhat subtle and unavoidable principle has huge ramifications. For example the power of a drill or any other machine is proportional to the volume, while the friction of the drills bearings and gears is proportional to their surface area. For a normalsized drill, the power of the device is enough to handily overcome any friction. However, scaling its length down by a factor of , for example, decreases its power by a factor of a billion while reducing the friction by only a factor of only a million. Proportionally it has times less power per unit friction than the original drill. If the original frictiontopower ratio was, say, , that implies the smaller drill will have times as much friction as power. The drill is useless.For this reason, while superminiature electronic integrated circuits are fully functional, the same technology cannot be used to make working mechanical devices beyond the scales where frictional forces start to exceed the available power. So even though you may see microphotographs of delicately etched silicon gears, such devices are currently little more than curiosities with limited real world applications, for example in moving mirrors and shutters.
Surface tension increases in much the same way, thus magnifying the tendency for very small objects to stick together. This could possibly make any kind of micro factory impractical even if robotic arms and hands could be scaled down, anything they pick up will tend to be impossible to put down. The above being said, molecular evolution has resulted in working cilia, flagella, muscle fibers and rotary motors in aqueous environments, all on the nanoscale. These machines exploit the increased frictional forces found at the micro or nanoscale. Unlike a paddle or a propeller which depends on normal frictional forces the frictional forces perpendicular to the surface to achieve propulsion, cilia develop motion from the exaggerated drag or laminar forces frictional forces parallel to the surface present at micro and nano dimensions. To build meaningful machines at the nanoscale, the relevant forces need to be considered. We are faced with the development and design of intrinsically pertinent machines rather than the simple reproductions of macroscopic ones.All scaling issues therefore need to be assessed thoroughly when evaluating nanotechnology for practical applications.
MATERIALS USED IN NANOTECHNOLOGY
Materials referred to as nanomaterials generally fall into two categories fullerenes, and inorganic nanoparticles. See also Nanomaterials in List of nanotechnology topics .The fullerenes are a class of allotropes of carbon which conceptually are graphene sheets rolled into tubes or spheres. These include the carbon nanotubes which are of interest both because of their mechanical strength and also because of their electrical properties.For the past decade, the chemical and physical properties of fullerenes have been a hot topic in the field of research and development, and are likely to continue to be for a long time. In April , fullerenes were under study for potential medicinal use binding specific antibiotics to the structure of resistant bacteria and even target certain types of cancer cells such as melanoma. The October issue of Chemistry and Biology contains an article describing the use of fullerenes as lightactivated antimicrobial agents. In the field of nanotechnology, heat resistance and superconductivity are among the properties attracting intense research.
A common method used to produce fullerenes is to send a large current between two nearby graphite electrodes in an inert atmosphere. The resulting carbon plasma arc between the electrodes cools into sooty residue from which many fullerenes can be isolated.There are many calculations that have been done using abinitio Quantum Methods applied to fullerenes. By DFT and TDDFT methods one can obtain IR, Raman and UV spectra. Results of such calculations can be compared with experimental results.Fullerene are a family of carbon allotropes, molecules composed entirely of carbon, in the form of a hollow sphere, ellipsoid, tube, or plane. Spherical fullerenes are also called buckyballs, and cylindrical ones are called carbon nanotubes or buckytubes. Graphene is an example of a planar fullerene sheet. Fullerenes are similar in structure to graphite, which is composed of stacked sheets of linked hexagonal rings, but may also contain pentagonal or sometimes heptagonal rings that would prevent a sheet from being planar.The fullerene was discovered in by Robert Curl, Harold Kroto and Richard Smalley at the University of Sussex and Rice University, who named it after Richard Buckminster Fuller, whose geodesic domes it resembles.
NANOPARTICLES
Nanoparticles or nanocrystals made of metals, semiconductors, or oxides are of particular interest for their mechanical, electrical, magnetic, optical, chemical and other properties. Nanoparticles have been used as quantum dots and as chemical catalysts.
Nanoparticles are of great scientific interest as they are effectively a bridge between bulk materials and atomic or molecular structures. A bulk material should have constant physical properties regardless of its size, but at the nanoscale this is often not the case. Sizedependent properties are observed such as quantum confinement in semiconductor particles, surface plasmon resonance in some metal particles and superparamagnetism in magnetic materials.Nanoparticles exhibit a number of special properties relative to bulk material. For example, the bending of bulk copper wire, ribbon, etc. occurs with movement of copper atomsclusters at about the nm scale. Copper nanoparticles smaller than nm are considered super hard materials that do not exhibit the same malleability and ductility as bulk copper.
The change in properties is not always desirable. Ferroelectric materials smaller than nm can switch their magnetisation direction using room temperature thermal energy, thus making them useless for memory storage. Suspensions of nanoparticles are possible because the interaction of the particle surface with the solvent is strong enough to overcome differences in density, which usually result in a material either sinking or floating in a liquid. Nanoparticles often have unexpected visual properties because they are small enough to confine their electrons and produce quantum effects. For example gold nanoparticles appear deep red to black in solution.The often very high surface area to volume ratio of nanoparticles provides a tremendous driving force for diffusion, especially at elevated temperatures. Sintering is possible at lower temperatures and over shorter durations than for larger particles. This theoretically does not affect the density of the final product, though flow difficulties and the tendency of nanoparticles to agglomerate do complicate matters. The surface effects of nanoparticles also reduces the incipient melting temperature.
