Carbon and making a model Buckyball
Studying material science allows new products to be made with greater efficiency and lower costs. The choice of material for a new product depends on the function of the new product and how its properties will enhance the product. A famous example is reinforced concrete. Concrete itself is strong under compression but weak under tension and steel is strong under tension but weak under compression. Put the two together and you have a very strong building material. Of course cost is also a consideration. Silver is a much better electrical conductor than copper but copper is considerably cheaper. So the choice of materials is a balance between properties, performance, cost and convenience, amongst other things.
Nanomaterial properties differ from their large scale properties because they have a greater surface-area-to-volume-ratio and if they are free to move then there is a greater chance of random motion (Brownian motion). They are likely to have greater reaction rates and may even be different colours from their large scale counterparts.
Carbon is the chemical element with symbol C and atomic number 6. It is non-metallic and tetravalent — making four electrons available to form covalent chemical bonds. There are three naturally occurring isotopes, with 12C and 13C being stable, while 14C is radioactive, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity.
Carbon has two main allotropes, graphite (of which graphene can be produced) and diamond. The allotropes occur because of carbon’s ability to form structures with different types of bonds. In diamond, a central carbon atom bonds to four different carbon atoms. A three-dimensional structure is produced by the bonding pairs of electrons repelling each other to form a tetrahedron shape. In diamond each carbon forms four single carbon bonds.
Properties of carbon
Diamond is very hard and difficult to chip or break. This is because the carbon atoms are tightly bonded to each other in all directions. A large number of covalent bonds have to be broken to chip diamond.
Diamond behaves as an insulator because all the electrons in the outer shell of the diamond atom are involved in bonding. There are no ‘free’ conduction electrons.
Graphite, e.g. pencil lead, is soft. The graphite sheets are weakly bonded by Van der Waals forces layer to layer. These bonds are easy to break, allowing sheets of graphite to be removed and the material appears soft.
Graphite is a conductor because the electrons in the delocalised double bond are not confined to a particular atom.
Graphene is very strong because the bonding between carbon atoms is reinforced by the partial double bond nature. It is one of the strongest materials tested. Measurements have shown that graphene has a breaking strength 200 times greater than steel.
Graphene is an excellent conductor of electricity and a very promising candidate for future electronic applications.
Graphene is impermeable. Not even a helium atom can penetrate a sheet of graphene (but it is not impermeable to H2).
The above right is a TEM of graphene.
Graphene is pure carbon in the form of a very thin, nearly transparent sheet, one atom thick. It is remarkably strong for its very low weight (100 times stronger than steel) and it conducts heat and electricity with great efficiency. While scientists had theorized about graphene for decades, it was first produced in the lab in 2004. Andre Geim and Konstantin Novoselov at the University of Manchester won the Nobel Prize in Physics in 2010 “for groundbreaking experiments regarding the two-dimensional material graphene”
The above image shows a lump of graphite, a graphene transistor and a tape dispenser which was donated to the Nobel Museum in Stockholm by Andre Geim and Konstantin Novoselov in 2010.
Single-atom-thick crystallites were extracted from bulk graphite by lifting graphene layers from graphite with adhesive tape then transferring them onto a silicon wafer.
Applications of graphene
In 2010 IBM scientists demonstrated the world’s fastest transistor made using graphene. Electrons travel at higher speed in graphene than in silicon.
Graphene has high optical transparency and high electrical conductivity so is an ideal candidate for electrodes for touchscreens, liquid crystal displays, organic photovoltaic cells and organic light emitting diodes (OLED). Graphene could replace the indium based electrodes in OLEDs, making them easier to recycle.
Due to its impermeability, graphene may be ideal as a sensor, detecting single molecules. Graphene could be coated with a thin layer of a polymer which absorbs molecules. The molecule absorption introduces a local change in electrical resistance of graphene, allowing detection of single molecules, making a very sensitive sensor.
Due to its great strength, graphene could potentially be used as a reinforcing material for composites from household plastics to building materials.
Another suggestion is to use a single layer of graphene to create a metamaterial covering to alter the scattered light from an object, so making an invisibility cloak.
Usable quantities of graphene are tricky to make and even trickier to handle. The process of separating it from graphite, where it occurs naturally, is difficult and will require technological development before it is economical enough to be used in industrial processes. Some progress has been made. In 2009 Professor Jonathan Coleman described a technique for separating graphite into graphene and coating the graphene sheets with soap molecules to prevent them returning to graphite. With its high yield and throughput this is an ideal method for industrial production of graphene.
Some researchers claim to have grown single layers of graphene. Graphene in the gas phase is absorbed on to copper and then on to a polymer to form a flexible screen.
Graphene can be rolled up to form nanotubes but it is not an easy process. By adding it to other materials it can change their conducting properties and tensile strength. Some laboratories are trying to extrude graphene.
In graphite a central carbon atom bonds to three different carbon atoms. To obey the octet rule (a chemical rule of thumb which states that atoms tend to combine in such a way that they each have eight electrons in their outermost shells) would suggest a double bond in the graphite structure. However the lengths of the bonds in graphite have been measured and found to be identical to each other, intermediate between a single and a double bond. This bonding is the same as is present in benzene.
The bonds in graphite are not confined to particular atoms but are shared by the carbons. This delocalised double bond makes the carbon atoms more strongly bonded to each other. For simplicity, the carbon atoms can be considered as bonded by strong single bonds.
The bonds in graphite repel each other to be as far away from each other as possible. This repulsion causes the carbon atoms in graphite to form a 2-dimensional structure called trigonal planar – one atom at the centre with three atoms at the corner of a triangle. Each atom forms 3 covalent bonds but consequence of this is the presence of delocalised electrons which give graphite is good conducting properties.
There are weak attractive forces between layers which is why graphite can be used to make marks on other materials. These marks are simply thin layers of graphite. Graphite is actually found in pencils and is used for writing or drawing. The weak force is called van der Waals force and is the sum of the attractive or repulsive forces between molecules (or between parts of the same molecule) other than those due to covalent bonds or the electrostatic interaction of ions with one another or with neutral molecules or charged molecules.
In mineralogy, diamond is a metastable allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centred cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at standard conditions. Diamond is renowned as a material with superlative physical qualities, most of which originate from the strong covalent bonding between its atoms. In particular, diamond has the highest hardness and thermal conductivity of any bulk material. Those properties determine the major industrial application of diamond in cutting and polishing tools and the scientific applications in diamond knives and diamond anvil cells.
Diamond has 4 strong covalent bonds
A fullerene is any molecule composed entirely of carbon, in the form of a hollow sphere, ellipsoid, tube, and many other shapes. Spherical fullerenes are also called buckyballs, and they resemble the balls used in football (soccer). Cylindrical ones are called carbon nanotubes or buckytubes. Fullerenes are similar in structure to graphite, which is composed of stacked graphene sheets of linked hexagonal rings; but they may also contain pentagonal (or sometimes heptagonal) rings
Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material. These cylindrical carbon molecules have unusual properties, which are valuable for nanotechnology, electronics, optics and other fields of materials science and technology. In particular, owing to their extraordinary thermal conductivity and mechanical (they have a high strength to weight ratio) and electrical properties, carbon nanotubes find applications as additives to various structural materials. For instance, nanotubes form a tiny portion of the material(s) in some (primarily carbon fibre) baseball bats, golf clubs, or car parts. They make ideal composites.
Nanotubes are members of the fullerene structural family. Their name is derived from their long, hollow structure with the walls formed by one-atom-thick sheets of carbon, called graphene. These sheets are rolled at specific and discrete (“chiral”) angles and the combination of the rolling angle and radius decides the nanotube properties; for example, whether the individual nanotube shell is a metal or semiconductor. Nanotubes are categorized as single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs). Individual nanotubes naturally align themselves into “ropes” held together by van der Waals forces, more specifically, pi-stacking.
Nanotubes can be imagined as a sheet of graphene rolled up and there are three different ways of rolling the sheet, giving the three different types of nanotube: armchair, chiral and zigzag. Although a nanotube appears to be a rolled up sheet it cannot be made that way. A common commercial technique is chemical vapour deposition (CVD) in which the atoms are deposited from hot gas.
The armchair configuration is a conductor of electricity while the chiral and zigzag forms are semiconductors. Electrons find it easier to flow in the armchair configuration than the other forms.
The armchair configuration of nanotubes is a conductor of electricity while the chiral and zigzag forms are semiconductors. Electrons find it easier to flow in the armchair configuration than the other forms.
Research is taking place into the use of nanotubes for drug delivery and their potential for energy storage, energy conversion devices, sensors and nanoscale semiconductor devices.
An object or a system is chiral if it is not identical to its mirror image, that is, it cannot be superposed onto it. A chiral object and its mirror image are called enantiomorphs or, when referring to molecules, enantiomers.
Buckminsterfullerene (or bucky-ball) is a spherical fullerene molecule with the formula C60. It has a cage-like fused-ring structure (truncated icosahedron) which resembles a soccer ball, made of twenty hexagons and twelve pentagons, with a carbon atom at each vertex of each polygon and a bond along each polygon edge.
It was first generated in 1985 by Harold Kroto, James R. Heath, Sean O’Brien, Robert Curl, and Richard Smalley at Rice University. Kroto, Curl and Smalley were awarded the 1996 Nobel Prize in Chemistry for their roles in the discovery of buckminsterfullerene and the related class of molecules, the fullerenes. The name is a reference to Buckminster Fuller, as C60 resembles his trademark geodesic domes. Buckminsterfullerene is the most common naturally occurring fullerene molecule, as it can be found in small quantities in soot. Solid and gaseous forms of the molecule have been detected in deep space.
Buckminsterfullerene is one of the largest objects to have been shown to exhibit wave–particle duality, as stated in the theory every object exhibits this behaviour. Its discovery led to the exploration of a new field of chemistry, involving the study of fullerenes.
Wave–particle duality is a theory that proposes that every elementary particle exhibits the properties of not only particles, but also waves. A central concept of quantum mechanics, this duality addresses the inability of the classical concepts “particle” or “wave” to fully describe the behaviour of quantum-scale objects. Einstein description: “It seems as though we must use sometimes the one theory and sometimes the other, while at times we may use either. We are faced with a new kind of difficulty. We have two contradictory pictures of reality; separately neither of them fully explains the phenomena of light, but together they do”.
Making a model Buckyball
This activity shows bonding and crystal structure. The curved ends of the nanotube contain pentagons; the walls are the normal hexagonal structure.
1) I had to unpack the parts and separate out the straws
2) I connected five black “atoms” with five of the red straws to make up a pentagon
3) I made 12 separate pentagons.
4) I started to join up the pentagons with white straws
5) I connected five pentagons around a central pentagon to form a sort of star.
6) I then continued to add straws to connect the five outer pentagons with each other. This will make the structure start to curve-up to form a bowl shape. It is half the Bucky Ball.
7) I made up two of these bowl shapes. Each had 6 pentagons and 5 hexagons
8) I started to join-up these two halves of the ball with more straws.
9) I continued to add straws to join up the model
My finished Buckyball