Nanotechnology is based on a unit of measure called a(n) _____.
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1 nm = 10-9 m (i) surface effects (i) top-down Nanolevel (Nanoscale)The SI3 unit of measurement of length is the metre which has been given the symbol m.Compared to the size of atoms and molecules, a metre is an enormous unit of length. So Chemists routinely use smaller units of measurement, such as the nanometre. The prefix "nano" indicates a billionth (a thousand millionth), that is, 1 divided by a 1,000,000,000, which is represented as: So 1 nanometre is 1 billionth of a metre, or,
For very small numbers like 0.000000001 scientists prefer to use scientific notation (exponential notation) to represent the number: 1 nanometre = 0.000000001 m = 1 × 10-9 m When using nanometres as a unit of measurement, nanometre is given the symbol nm: 1 nanometre = 1 nm The table below gives the names and abbreviations used for common measurements of length used in chemistry:
A nanoparticle has a diameter between 1 nm and 100 nm. 1 nm = 10-9m 100 nm = 100 × 10-9 m = 10-7 m So, a nanoparticle has a diameter between 10-9 m and 10-7 m and is not visible to the naked eye.
How many atoms could you place side by side to make up a linear nanoparticle with length of 1 nm ?
How many atoms could be placed in a line to make a line 100 nm long?
So scientists studying nanoparticles are studying very small particles that are not visible to the naked eye and are made up of a relatively small number of atoms. Surface EffectsAt the nanolevel, a nanoparticle has a greater proportion of its atoms at the surface compared to a larger particle made up of the same atoms.
Now atoms are usually modelled as spheres not cubes, and when atoms cluster together to form a nanoparticle it is also thought of as being spherical, so scientists usually talk about the ratio of the surface area of the spherical particle to its volume when they want to describe the proportion of atoms at the surface of the sphere:
A 3 nm particle has about 50% of all its atoms at the surface, but a particle tens time larger, a 30 nm particle, only has about 5% of all its atoms at the surface. Rate of reaction is increased by using nanoparticles rather than the bulk material. Silver is known to kill bacteria, but the cost of using bulk silver for this purpose is high. However, the antibacterial properties of silver are enhanced as the particle size decreases, so nanoparticles of silver can be cost effectively incorporated into medical dressings. The chemical activity of a substance can be enhanced so much at the nanoscale that a material we usually think of as being unreactive becomes reactive! Similarly, when you buy bulk flour at the supermarket you do not expect it to react spontaneously with air because the particles of flour are quite large, but, very fine flour "smoke" particles at the mill can ignite spontaneously in air. If you add silver as a bulk material such as a strip of silver foil to hydrochloric acid, you won't see bubbles of hydrogen gas given off, there is no apparent reaction. If, however, you grind down the bulk silver foil to produce silver nanoparticles you will find that the silver nanoparticles rapidly react with hydrochloric acid. Similarly, using nanoparticle-sized catalysts would improve the rate at which the catalyst converts reactants to products because it provides a greater surface area on which the reaction can take place. This means you could use less mass of expensive catalysts, reducing the costs of manufacturing a product. Cobalt nanoparticles are used in the production of adipic acid (hexanedioc acid) which is then used to produce the polymer nylon-6,6 on an industrial scale. It is hoped that the use of nanoparticle catalysts will improve the efficiency and cost effectiveness of future fuel cells. Since nanoparticles have a greater percentage of their atoms at the surface compared to the bulk material, it follows that nanoparticles have a greater proportion of their mass at the surface compared to the bulk material. Having a larger proportion of their atoms at the surface results in nanoparticles interacting more strongly with solvent molecules compared to interactions between bulk material and solvent. So, while a more dense bulk material will sink if added to a less dense solvent, nanoparticles of the same material interact strongly with the molecules making up a solvent so that even very dense nanoparticles can be suspended in a less dense solvent.5 Quantum EffectsNanoparticles are so small that their electrons are confined, resulting in what scientists refer to as quantum effects. At the nanolevel, properties such as melting point, fluorescence, electrical conductivity, and magnetic permeability, as well as chemical reactivity, change as a function of the size of the particle. Bulk gold, for example, melts at 1064oC, but 2.5 nm gold particles melt at the much lower temperature of approximately 300oC. Nanoparticles interact with light in a different way compared to the bulk material so that nanoparticles tend to absorb more solar radiation than the bulk material.One of the physical properties of bulk gold is its yellow colour. Zinc oxide in the bulk material is white, and is the main component in "zinc cream" that has
been keeping Australian's noses sun-burn free for decades by absorbing ultraviolet radiation. Similarly, titanium dioxide in the bulk material is a white solid and is commonly found in house paint because of its ability to reflect visible light. Nanoparticles made up of cadmium and selenium are used to produce quantum dots. Quantum dots6 are semiconducting fluorophores, that is, they absorb light at one wavelength and emit light of a different wavelength. The wavelength of the light emitted depends on the size of the quantum dot, a larger quantum dot emits light of a longer wavelength:
Because quantum dots produce monochromatic light, they have been used to improve the quality of the colour emitted by light-emitting diodes (LEDs) resulting in better television and computer screen displays. It is thought that in the future quantum dots will be able to increase the efficiency and reduce the cost of future photovoltaic cells. Bulk
material of carbon such as diamond is an electrical insulator, while graphite is conducts electricity in one direction. Carbon nanotubes, long tubes made of carbon but only a nanometre in diameter, are semiconductors, sometimes they conduct electricity and sometimes they don't, which means they could be used to act like switches on computer chips. NanomanufacturingThere are two main approaches to nanomanufacturing. These are known as:
The bottom-up approach to manufacturing was first demonstrated in 1989 by a group of IBM scientists who used a scanning probe microscope to move 35 individual xenon atoms around on a copper surface to spell out IBM,
demonstrating that it is possible for us to build up nanostructures one atom at a time. It took a whole day to this, so it was a very time-consuming demonstration! There is much interest in the idea of "self-assembly", a process in which molecular-scale components can be brought together and will spontaneously "self-assemble" from the bottom up into ordered structures. Safety of NanoparticlesAre nanoparticles harmful to us or to the environment?We don't really know... We do know that nanoparticles are small enough to pass through many of the biological membranes designed to exclude larger particles, but .... We have been exposed to nanoparticles our whole life, and our parents, and their parents, etc, were also exposed to nanoparticles. Nanoparticles are not new, only our scientific study of them is new. But it is entirely likely that during your lifetime you will be exposed to a greater concentration and variety of nanoparticles than your parents were. We know that the level of "harm" caused to us by bulk substances depends on a number of factors such as what the substance is made up of, what size and shape the particles are, and how the particles enter the body, but nanoparticles exhibit different properties to the bulk material. Particles can enter the human body when we eat, drink or breathe, and, because nanoparticles are so small they may also be absorbed through the skin. If we take in particles with our food and drink, what happens? We know that nanoparticles have a much greater reaction rate than bulk materials, will they speed up biochemical reactions in an unpredictable way? Or can they provide alternative biochemical pathways that result in toxic products? Nanoparticles will increasingly be ingested via the consumption of agricultural products because nanoparticles hold particular appeal for agriculture, the smaller the particles of the herbicides, pesticides, and fungicides used, the less the mass of these chemicals required would be, lowering the overall cost of agricultural production. Future of NanotechnologyWe are already seeing increased government and industrial spending on nanotechnology research and development.Nanotechnology as a science is still in its infancy, there are enormous opportunities for future scientific investigation not only of the properties of nanoparticles, but also the study of how to produce the nanoparticles, how to apply this knowledge to the production of engineered nanoparticles, and to the investigation of the biological and environmental effects of nanoparticles. 1 The term was coined in 1974 by Norio Taniguchi who referred to this as the ability to engineer materials preceisely at the nanometre scale. 2 You will also see the alternative spelling for metres as meters. In general, it is better to use "metre" when referring to the measurement, and "meter" for an instrument that measures (such as spectrometer or voltmeter) or for a word indicating a specified number of measures (such as diameter). 3 SI is the abbreviation for Système Internationale
d'Unités. It is a unified version of the metric system agreed upon by the General Conference of Weights and Measures in 1960 and is used world-wide. 4 In 1967 the 13th CGPM abolished the name "micron" in favour of the SI term "micrometre" (you will also see the alternative spelling micrometer). 5 This type of mixture is referred to as a colloidal dispersion, and is a two phase system. The nanoparticles are referred to as the "dispersed phase" and the liquid which we referred to as the solvent should technically be referred to as the dispersion medium. 6 The term "quantum dot" was coined n 1988 by Mark Reed and is often abbreviated to QD. 7 Janus, the Roman god of gates and beginnings, is shown with two faces, one on the front of his head and the other on the back of his head. 8 The term "surfactant" is a contraction of the term "surface active agent" and is commonly applied to the molecules responsible for the cleaning action of soaps and detergents. |