C2: Material Choices

• The materials that we use are chemicals or mixtures of chemicals and include metals, polymers and ceramics.
• Some materials can be made or obtained from living things e.g.cotton, paper, silk, wood,etc.
• Synthetic materials, produced by chemical synthesis, can be made as alternatives to these.
• The raw materials may be taken from the Earth's crust.
• Crude Oil - When extracted its a thick, black, sticky liquid containing hydrocarbons which are chain molecules containing only hydrogen and carbon atoms.
• Different hydrocarbons have different boiling points, their molecular chains are different lengths
• The strength of the forces between the hydrocarbon molecules increases as the length of the molecule increases.
• More energy is needed to break the forces between the molecules in the liquid so that they can move freely as a gas. So, larger molecules have higher boiling points.
• This means that hydrocarbons can be separated by fractional distillation into groups of hydrocarbons with similar lengths.
• The petrochemical industry refines naturally occurring crude oil to produce fuels, lubricants and raw materials for chemical synthesis. Only a small proportion of crude oil is used in chemical synthesis, most of it is used for fuels.

• Unvulcanised Rubbers - Properties-low tensile strength, soft, flexible/elastic. Uses-erasers, rubber bands.
• Vulcanised Rubbers - Properties-high tensile strength, hard, flexible-elastic. Uses-car tyres, conveyer belts, shock absorbers.
• Plastic (Polythene) - Properties-light, flexible, easily moulded. Uses- plastic bags, clingfilm, water pipes.
• Plastic (Polystyrene) - Properties-light, insulation properties, water resistant. Uses-meat trays, egg cartons, coffee cups, packaging.
• Synthetic Fibres (Nylon) - Properties-lightweight, tough, blocks ultraviolet light. Uses-clothing, climbing ropes.
• Synthetic Fibres (Polyester) - Properties-lightweight, waterproof, tough. Uses-clothing, bottles.
• The properties of the materials used will affect the effectiveness of the end product, so manufacturers always test and assess them carefully beforehand.

• Polymerisation is an important chemical process in which small hydrocarbon molecules called monomers are joined together to make very long molecules called polymers.
• During a chemical reaction, the number of atoms of each element in the products must be the same as in the reactants so count the atoms.
• Polymerisation can be used to create a wide range of different materials that have different properties and therefore can be used for different purposes.
• Many traditional (natural) materials have been replaced by polymers because of their superior properties.
• Polymer - Polyethene. Monomer - Ethene. Use - Carrier bags. Traditional Material - Paper. Reason - Stronger; waterproof.
• Polymer - Polychloroethene PVC. Monomer - Chloroethene. Use - Window frames. Traditional Material - Wood. Reason - Unreactive; does not rot.

• The properties of solid materials depend on how the particles they are made from are arranged and held together.
• Natural rubber is very flexible. It consists of a tangled mass of long-chain molecules.
• Although the atoms in each molecule are held together by strong covalent bonds, there are very weak forces between the molecules so they can easily slide over one another, allowing the material to stretch.
• Rubber has a low melting point as little energy is needed to separate the molecules.
• Materials with strong forces between the molecules (covalent bonds or cross-linking bridges) have high melting points as lots of energy is needed to separate them.
• As the molecules cannot slide over one another, these materials are rigid and cannot be stretched.

Modifications can produce changes to the properties of polymers. These can include:

• increasing the chain length - longer molecules are stronger than shorter ones.
• cross-linking - cross-links are formed by atoms bonding between the polymer molecules, so they are no longer able to move. This makes for a harder material. An example of this is vulcanisation, when sulfur atoms form cross-links between rubber molecules. Vulcanised rubber is used to make car tyres and conveyer belts.
• plasticisers - adding plasticisers makes a polymer softer and more flexible. A plasticiser is a small molecule that sits between the molecules and forces the chains further apart. The forces between the chains are, therefore, weaker and so the molecules can move more easily. Plasticised PVC is used to make children's toys.

• A polymer can also be modified by packing the molecules more closely together to form a crystalline polymer. The intermolecular forces are slightly stronger so the polymer is stronger, more dense and has a slightly higher melting point.

• Nanoscience refers to the study of materials that are 1-100 nanometres in size, which is roughly the size of a few atoms. One nanometre is one billionth of a metre. (A human hair is around 20000nm in diameter and a microbe is around 200nm in diameter.)
• Nanotechnology is the science of building things on a very tiny scale. It is the understanding and control of matter at dimensions between approximately 1 and 100 nanometres. Nanotechnology is a growing industry.
• Nanoscale materials are not new. Naturally occuring materials, such as seaspray and liposomes,  have always existed. However, it was not until the early 1980s that they were identified by using scanning tunnelling microscopes.
• Nanoscale materials are designed to do specific jobs. For example, nanoparticles of titanium dioxide are added to sunscreen as they are very efficient at absorbing ultraviolet radiation. They are also being developed for use within medicine and dentistry, as well as in the car industry and product-specific catalysts.
• Some nanoscale materials are formed accidentally as a result of other chemical reactions, e.g. the smallest particles from the combustion of fuels.

• Nanotubes and buckyballs are nanoscale objects made of carbon atoms. They have been used in the manufacture of sports equipment, such as badminton rackets, for many years. In the future they are likely to play an important role in electronic systems.

• Nanoscale particles have different properties to larger particles of the same material. E.g. :
• nanoparticle electrons can move through an insulating layer of atoms
• nanoparticles are more sensitive to light, heat and magnetism
• nanoparticles in sunscreens and cosmetics absorb and reflect the harmful ultraviolet rays in sunlight
• nanoparticles can be added to glass to repel water and keep windows clean.

• Many of these properties can be explained by the much larger surface area of the nanoparticles compared to their volume.
• This means that nanoparticles can be used to modify the properties of existing materials, such as polymers, to make them stronger, stiffer, lighter, etc.

• In recent years a greater awareness of contact disease transmission and personal hygiene has led to the development of antibacterial fibres to protect wearers against the spread of bacteria and diseases. Researchers have found that silver nanoparticles can destroy many types of bacteria.
• Using this knowledge, scientists have developed antibacterial fibres containing silver nanoparticles that are woven into textiles and used to make clothes. Many leading sports-clothing manufacturers now use this silver oxide fibre technology. One of the special features of the clothing is that it has antibacterial properties, which keep garments fresh.
• Golf clubs are now much lighter, stronger and more efficient than they used to be, thanks to nanometal coatings. Nanometals have a crystalline structure and, although they are hundreds of times smaller than traditional metals, they are four times stronger. Golf balls are now treated with nanoscale properties that allow them to travel in straighter lines.
• Leading manufacturers of sports equipment have also started adding nanoscale silicon dioxide crystals to tennis rackets. The resulting polymer gives increased performance, without changing the weight.

• Nanotechnology is still in the early stages of development. New materials, with very useful properties, are being developed all the time.
• Nanotechnology has a variety of potential applications in biomedical, optical and electronic fields. For example, it could be used to create secure communication systems, detect and eradicate small tumours, help in the diagnosis of diseases and help in the development of microscopic surgery that would not leave scars.
• It is important to remember that nanoparticles can be dangerous in certain circumstances. For example, nanoparticles in wateer could be dangerous if they were consumed. Nanoparticles may have other harmful effects on health that are currently not known about.
• Some people and organisations are extremely concerned that products with nanoparticles are being introduced before they have been fully tested. It takes a long time to carry out a full investigation and any harmful health effects may be apparent for many years.
• Regulations for the development of new techniques and products do exist. A report by the Royal Society suggests that these regulations are adequate to deal with most of the nanotechnology products.