Nanotechnology and Human Health

Nanotechnology Revisited

Now that we have a grasp of the structure of matter, and how atoms and molecules fit into that structure, let's revisit nanotechnology. Nanotechnology is a new field of scientific study that involves manipulating individual atoms and molecules to create new things on an extremely small scale. It builds things from the bottom up-atom by atom, and molecule by molecule. The ability to control how atoms and molecules are put together in order to precisely control the characteristics of what you are making is the basis of nanotechnology. You might ask yourself how the manipulation of atoms or molecules affects the characteristics of a substance. Carbon provides a good example of how the differences in the ways atoms are assembled can result in materials with different characteristics. The differences in these characteristics exemplifies that molecules have size and shape: in addition, the shape of a molecule affects its properties. To date, scientists are aware of the following different physical forms (or allotropes) of carbon: graphite, coal, diamond, buckyballs, and carbon nanotubes, all of which occur in the natural environment. Graphite, coal, and diamond exist at the macro scale or the scale that we can see things with our naked eye. Buckyballs and nanotubes exist at the nanoscale and can only be seen with powerful microscopes. In each of these forms, the carbon atoms interact with each other differently, resulting in materials that exhibit different properties.

Graphite

Graphite has a layered flat structure. The structure itself is rather complex, but it is primarily in a 2 dimensional plane and the atoms of carbon are arranged in a pattern similar to chicken wire. In graphite, each carbon atom bonds to three other carbon atoms and form single layers of hexagonal-shaped carbon atom rings. These hexagonal shaped rings stack on top of each other in sheets. The material graphite is relatively soft, because the structure consists of these flat sheets that can slide across each other. Think of playing cards, if you stand them on their edge they are reasonably strong but when laid flat they will slide over other cards and will bend or break if too much force or pressure is used. Soft, light, and flexible, this is the form of carbon we commonly find in the lead of a pencil; it is also the basic substance in coal. When we write with a graphite pencil small pieces of the graphite rub off onto the paper by friction and then stick to the paper, forming whatever letters or shapes were drawn. Graphite molecules within the sheets are held together through covalent bonding. Each atom uses three of its electrons to form simple bonds with its three closest neighbors. Graphite has the sensation of a slippery powder and is often used as a dry lubricant on locks and athletic equipment. Some of the properties of graphite include a high melting point, insolubility in water and organic solvents, and good conduction of electricity. ¹⁹

Diamond

Diamond atoms are arranged into a 3 dimensional solid structure, also formed through covalent bonding. The structure is an extended 3-D network in which one carbon atom is covalently bonded to four other carbon atoms. Diamond's crystal structure makes it extremely hard, suitable for cutting and grinding through industrial steel and other heavy-duty, industrial-strength manufactured materials. It is the hardest known solid. Diamond has a very high melting point and is not soluble in water or other organic solvents because of its strong carbon-carbon covalent bond. In addition, it does not conduct electricity because all of the electrons are packed tightly between the atoms and cannot move easily throughout the solid; diamond consequently is an insulator. When we think of diamonds we think of them as precious gems with a magnificent brilliance and shine. Scientists, on the other hand, think of diamonds with respect to their range of phenomenal and exceptional properties. In addition to being the hardest known material to date, it is also the stiffest and least compressible. Diamonds are the best thermal conductors with very low thermal expansion. They do not react with most acids or bases. ²⁰

Buckminsterfullerene (Buckyballs)

In 1985 a team of three chemists, Robert Curl Jr., Sir Harold Kroto, and Richard Smalley discovered a new form of carbon made up of 60 carbon atoms. The newly discovered carbon molecule was given the official name Buckminsterfullerene; the name given to the new carbon family was fullerenes. Fullerenes are three-dimensional cage-like spheres that closely resemble a soccer ball consisting of a spherical pattern of hexagons and pentagons. ²¹ Individual buckyballs are hard, possibly harder than diamonds. As a bulk substance, however, they are relatively soft, because every buckyball can move with respect to all of the others. Potential applications for buckyballs currently being investigated include its use as a lubricant or superconductor. ²²

(Note: A good activity to introduce here is one that involves cutting and folding a net (a truncated icosahedron) resulting in a buckyball-like structure.)

Carbon Nanotube

In 1991, six years after scientists discovered, or should I say recognized the buckyball structure, Sumio Lijima, a Japanese physicist, recognized a different form of carbon. He noticed nano-sized threads in a smear of soot. These threads turned out to be very thin threads of pure carbon only a few nanometers in diameter but many nanometers long. Carbon nanotubes are long tubular molecules of carbon structurally similar to buckyballs. They can be described as cylindrical fullerenes that have an extended structure resembling a tube of chicken-wire fencing. A carbon nanotube can carry an electrical current and, therefore, may be thought of as the world's smallest wire. ²³ Carbon nanotubes can act as semiconductors, which is a substance that will conduct electricity under certain environmental circumstances and not under others. This property makes them good materials for controlling electrical current, which is important for the manufacture of computer chips because they can act like small switches turning on and off determined by whether they are allowing electrons to flow or not. Carbon nanotubes are incredibly strong, stronger than steel, very lightweight, and flexible. They are one of the strongest and most rigid materials known to date and possibly the strongest material known. They are currently being used in tennis rackets and bicycles, making these items very strong and extremely lightweight. (An activity involving the construction of different molecules based on a set of materials is a good illustration of this concept.)