Nanoparticles (these are materials which are of size 10-9 m) consist of several tens or hundreds of atoms or molecules and may have a variety of sizes and morphologies
these can be:amorphous, crystalline, spherical, needles, etc…
Such nanoparticles are creating a new category of materials, which
:: is different either from conventional bulk materials or from atoms and,
:: are the smallest units of matter.
Nanoscale materials are used in electronic, magnetic optoelectronic,biomedical,pharmaceutical, andmaterials applications.
Relative sizes of physical bodies
Nanoparticles are small clusters of atoms about 1 to 100 nanometers long.
'Nano' derives from the Greek word "nanos", which means dwarf or extremely small. It can be used as a prefix for any unit like a second or a liter to mean a billionth of that unit. A nanosecond is a billionth of a second. A nanoliter is a billionth of a liter. And therefore a nanometer is a billionth of a meter or 10-9 m.
A brief intro
In nanotechnology, a particle is defined as a small object that behaves as a whole unit in terms of its transport and properties. Particles are further classified according to size: in terms of diameter, fine particles cover a range between 100 and 2500 nanometers. On the other hand, ultrafine particles are sized between 1 and 100 nanometers.
Particles and comparisons
Similar to ultrafine particles, nanoparticles are sized between 1 and 100 nanometers. The reason for this double name of the same object is that, during the 1970-80's, when the first large-scale projects were running with "nanoparticles" in the USA and Japan, they were called "ultrafine particles" (UFP).
High surface area is critical factor in performance of catalysis and structures such as electrodes allowing imporvement in such technologies as fuel cells or batteries.
The large surface area of nano particles also results in a lot of interactions between the intermixed materials in nano composites leading to special properties such as increased strength and increased chemical or heat resistance.
Nanoparticles are often defined as particles of less than 100nm in diameter
There is an increase in ratio of surface area to volume.
The increase in surface to volume ratio which is the gradual progression as the particle get smaller leads to an increase dominance of the behaviour of atoms on the surface of particles over that those in the interior of the particles
Nanoparticles are the smallest identifiable pieces of a material or substance. These particles can be taken from any material, however the size of any one particle cannot exceed one nanometer in size. Their size is indicated in the "nano" prefix, meaning one billionth so one nanometer is approximately one billionth of a meter. Something this small is not visible to the human eye, so high-powered microscopes are required to work with these materials. Their unusually small size opens up a whole new world of science and discovery.
They have been used for very long time.Probably the early use being in glazes for
early dynasty chinese porcelain.A roman cup called the Lycurgus cup, used
nanosized gold clusters to create different colors depending on whether It as illuminated from the forth or back.
The cause of the effect was not known to those who exploited this.
Carbon black is the most famous exmaple of nanoparticle which has been produced in huge quantitiy for decades.
Roughly 1.5 billion tons are poduced every year.
Nano paticles are currently made up of many materials. The most common is ceramics which are best split in to metal oxides ceramices such as titanum, aluminium, zinc, metal
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 nano-scale size-dependent properties are often observed.
Thus, the properties of materials change as their size approaches the nanoscale and as the percentage of atoms at the surface of a material becomes significant.
For bulk materials larger than one micrometer
(or micron), the percentage of atoms at the
surface is insignificant in relation to the
number of atoms in the bulk of the material.
The interesting and sometimes unexpected
properties of nanoparticles are therefore
largely due to the large surface area of the
material, which dominates the contributions
made by the small bulk of the material.
Other size-dependent property changes include quantum confinement in semiconductor particles, surface plasmon resonance in some metal particles and superparamagnetism in magnetic materials. Ironically, the changes in physical properties are not always desirable.
Ferroelectric materials smaller than 10 nm can switch their magnetisation direction using room temperature thermal energy, thus making them unsuitable for memory storage.
Suspensions of nanoparticles are possible since the interaction of the particle surface with the solvent is strong enough to overcome density differences, which otherwise usually result in a material either sinking or floating in a liquid.
Nanoparticles also often possess unexpected optical properties as they are small enough to confine their electrons and produce quantum effects. For example gold nanoparticles appear deep red to black in solution.
Suspensions and other properties
The high surface area to volume ratio of nanoparticles provides a tremendous driving force for diffusion, especially at elevated temperatures.
Sintering can take place at lower temperatures, over shorter time scales 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 complicates matters. Moreover, nanoparticles have been found to impart some extra properties to various day to day products.
There are variety of techniques for producing nanoparticles.
They fall in to three categoriesCondensation from a vaporChemical synthesisSolid sate processes such as millingParticles then can be coated with
hydrophilic substances or hydrophobic substances depending on desired use.
Used to make metallic and metal oxide ceramic nano particles.
It involves evaporation of solid metal followed by condensation of to form nano sized clusters that settles in the form of a powder
Various approaches to vaporize the metal can be used. And variation of medium in which or into which the vapor is to released affects the nature and size of the particles.
The main advantage of this technique is low contamination. Final particle size can be controlled by variation in temperature, gas environment and evaporation rate.
Most widely used chemical synthesis technique consist essentially of growing nanoparticles in a liquid medium containing various reactants. This is typified by sol gel approach and is also used to create this technique is better than the condensation technique for controlling the final shape of the nano particles.
These techniques are usually low cost and high volume but contamination from precursor chemical can be a problem.
Grinding and milling can be used to create nano particle
The milling material, milling time and atmospheric material affects resultant nano particles.
This approach is used to make nanoparticles from material that don’t readily lend them with previous two techniques.
Contamination from the parent material can be an issue.
Solid state processes
Nanoparticle research is currently an area of intense scientific research, due to a wide variety of potential applications in biomedical, optical, and electronic fields. Nanoparticles are of great scientific interest as they are effectively a bridge between bulk materials and atomic or molecular structures
Iron oxide nanoparticles can used to improve MRI images of cancer tumors. The nanoparticle is coated with a peptide that binds to a cancer tumor, once the nanoparticles are attached to the tumor the magnetic property of the iron oxide enhances the images from the Magnetic Resonance Imagining scanUsing gold nanoparticles embedded in a porous manganese oxide as a room temperature catalyst to breakdown volatile organic compounds in air.
USES OF DIFFERENT NANOPARTICLES
Nanoparticles coated with proteins that attach to damaged portions of arteries. This could allow delivery of drugs to the damaged regions of arteries to fight cardiovascular disease.
Magnetic nanoparticles that attach to cancer cells in the blood stream may allow the cancer cells to be removed before they establish new tumors.
A layer of closely spaced palladium nanoparticles that
detect hydrogen. When hydrogen is absorbed
the palladium nanoparticles swell, causing
shorts between nanoparticles which lowers the
resistance of the palladium layer.
Quantum Dots (crystalline nanoparticles) that
identify the location of cancer cells in the body.
Combining gold nanoparticles with organic molecules
to create a transistor known as a NOMFET
(Nanoparticle Organic Memory Field-Effect
Nanoparticles that deliver chemotherapy drugs directly to cancer cells.
Iron nanoparticles used to clean up carbon tetrachloride pollution in ground water.
Silicon nanoparticles coating anodes of lithium-ion batteries to increase battery power and reduce recharge time.
Silicate nanoparticles used to provide a barrier to gasses (for example oxygen), or moisture in a plastic film used for packaging. This could reduce the possibly of food spoiling or drying out.
Zinc oxide nanoparticles dispersed in industrial coatings to protect wood, plastic and textiles from exposure to UV rays.
Silver nanoparticles in fabric that kills bacteria making clothing odor-resistant.
The atomic force microscope (AFM) is ideally suited for characterizing nanoparticles. It offers the capability of 3D
visualization and both qualitative and quantitative information on many physical properties including size, morphology, surface texture and roughness. Statistical information, including size, surface area, and volume distributions, can be determined as well. A wide range of particle sizes can be characterized in the same scan, from 1 nanometer
AFM- ATOMIC FORCE MICROSCOPE
AFM can be performed in liquid or gas mediums. This capability can be very advantageous for nanoparticle characterization. For example, with combustion-generated nanoparticles, a major component of the particles are volatile components that are only present in ambient conditions.