Lycra® is a stretchy artificial fibre. It is used to make sports clothing such as wetsuits, and with other fibres to make comfortable clothing with a snug fit. Its molecules have a stretchy section that make it soft and rubbery, and a rigid section that makes it tougher than rubber. Lycra® is lightweight but doesn't get damaged by sunlight, sweat or detergents - all of which can make other materials wear out.

Thinsulate® fibres are much thinner than most other artificial fibres. They form a dense tangled web of fibres that trap a lot of air and reflect heat. This reduces heat loss, so clothes containing this material keep you very warm. The fibres also absorb very little water, so they still keep you warm if the clothes get wet.

Carbon fibres

Carbon in the form of graphite is soft, slippery and easily broken. But very thin filaments of carbon are very stiff. These carbon fibres are useful for reinforcing other materials to make them tougher. They are embedded in strong plastics to make composite materials. These are usually very strong but lightweight, so they are used for skateboards, boat hulls and high performance sports equipment.

Kevlar®

Kevlar® is a very strong artificial fibre. It is woven to make a material that is used for light and flexible body armour. It is strong and tough because:

• its molecules can pack closely together
• there are chemical bonds between adjacent molecules

Teflon®

Teflon® is the trade name for a polymer called polytetrafluoroethene or PTFE. It is very slippery so it is used to make non-stick coatings for pans. It is also used in clothing to make it difficult for dirt to stick, and it is used in Gore-Tex®. PTFE is also unreactive, so it is used to make pipes and containers for chemicals.

A section of a Teflon® molecule

Gore-Tex®

Gore-Tex® fabric

Gore-Tex® is a fabric that is designed to keep you dry in the rain without getting sweaty. It contains a layer of plastic based on PTFE. This contains very many tiny holes called pores. There are around 14 million pores per square millimetre. Each one is too small for water droplets to pass through, but big enough to let water molecules from sweat go through. This makes a 'breathable' fabric which can also be combined with insulation such as Thinsulate® to make outdoor clothing that keeps you dry and warm.

Gore-Tex® fabric is a sandwich of materials

Beer and wine are alcoholic drinks made by fermentation reactions that use yeast to convert sugars into ethanol. There are harmful effects and social problems because of ethanol in drinks.

Intelligent packaging keeps food fresh by removing water from the food, or stopping it reacting with oxygen.

Emulsifiers have a 'water-loving' head and a 'water-hating' tail. These substances allow oil and water to mix so they can become emulsions such as mayonnaise.

Making beer and wine

Ethanol

Ethanol is the type of alcohol found in alcoholic drinks such as wine and beer.

Structure of ethanol

formulachemical structureball-and-stick model C₂H₅OH

Sugar from plant material is converted into ethanol and carbon dioxide by fermentation. The enzymes found in single-celled fungi - yeast - are the natural catalysts that can make this process happen. Here are the word and balanced formulae equations:

sugar → ethanol + carbon dioxide

C₆H₁₂O₆ 2C₂H₅OH + 2CO₂

Fermentation usually works best at around 37ºC. It is a slow process and several weeks or more are usually needed to produce an acceptable alcoholic drink.

Beer

The sugars for beer-making come from boiling barley in water. Hops are added to adjust the flavour of the beer.

Wine

The sugars for wine-making come from grape juice. Different varieties of grapes are used to produce wines with different flavours. Wine contains a higher proportion of ethanol than beer does, because grape juice contains a higher concentration of sugars than barley in water.

Problems with alcoholic drinks

Alcoholic drinks

Ethanol is a depressant - it slows down signals in the nerves and brain. Small amounts of alcohol help people to relax, but greater amounts lead to a lack of self-control and loss of judgement. Drinkers may put themselves in dangerous situations, and may not realise how much they are drinking. They may fall ill, or become unconscious.

Ethanol is also toxic. Yeast are actually killed by the ethanol they produce. Long-term effects of drinking excessive amounts of alcoholic drinks include damage to the liver and brain. It may also cause weight gain, and is addictive.

Social issues

People suffering from 'hangovers' after drinking alcoholic drinks may be unable to function normally the next day. This puts strain on their family and their colleagues, and can lead to family problems, lost work and missed business.

Health issues

Ethanol causes damage to the liver, and leads to a risk of stroke or heart disease. This causes problems both for the drinker, and for those around them. Such diseases require the resources of the Health Service, which means it has less to spend on treating other illnesses.

Other alcohol-related problems include:

• accidents caused by people who drive or use machinery while drunk
• vandalism, fighting and other forms of anti-social behaviour
• family violence and breakdown

Keeping food fresh

Food goes off because of:

• bacteria and fungi that grow on or in the food
• chemical reactions that take place in the food, such as fats reacting with oxygen to make rancid products

Food is also spoiled if it gets damaged or crushed.

Stopping microbes

Bacteria and fungi are living organisms. They need water and oxygen - as well as the food itself - to grow and reproduce. If one or both of these is taken away, the microbes are unable to survive and the food will last longer.

Water can be removed by drying the food. Modern ‘freeze-drying' methods allow many food items to be dried so that they last longer. Freeze drying is popular for instant drinks, packet soups and fruit pieces in breakfast cereals

Oxygen can be restricted just by packaging the food in plastic, or sealing it in an air-tight container. However, the food itself contains some oxygen, and microbes can still survive in it. The air in modern packaging is often replaced by gases such as nitrogen. This restricts the amount of oxygen available, so microbes cannot grow and reproduce. There are other benefits to this method, too:

• fats in the food cannot react with oxygen to produce substances with rancid smells and flavours
• substances in sliced fruit and vegetables cannot oxidise and turn the food brown
• crisps and other easily damaged foods are protected from being crushed

Immiscible liquids

Immiscible liquids do not mix together. For example, if you add oil to water, the oil floats on the surface of the water. And if you shake the two together then leave them to stand, tiny droplets of oil float upwards. They join together until eventually the oil is floating on the water again. To stop the two liquids separating, we need a substance called an emulsifier.

Emulsifiers

Emulsifiers are molecules that have two different ends:

• a hydrophilic end - water-loving - that forms chemical bonds with water but not with oils
• a hydrophobic end - water-hating - that forms chemical bonds with oils but not with water

Lecithin is an emulsifier commonly used in foods. It is obtained from oil seeds and is a mixture of different substances. A molecular model of one of these substances is seen in the diagram.

Emulsifier molecules

The hydrophilic 'head' dissolves in the water and the hydrophobic 'tail' dissolves in the oil. In this way, the water and oil droplets become unable to separate out. The mixture formed is called an emulsion.

Emulsions

Mayonnaise and emulsion paints are emulsions, but there are others - such as the two in the table.

Components of emulsions

emulsionmajor componentminor component butter fat water milk water fat

Nanoparticles range in size from 100 nm to 1 nm and are far too small to see with a microscope. They have remarkable properties that are different from the same substance in bulk. They are already being used in consumer products but there are some uncertainties about their safety.

Measurements

The table shows some of the units used for measuring length. As you go down the table, each unit is one thousand times smaller than the one above it.

Some of the units used for measuring length

Unit nameUnit symbolMeaning gigametre Gm one billion metres megametre Mm one million metres kilometre km one thousand metres metre m one metre millimetre mm one thousandth of a metre micrometre µm one millionth of a metre nanometre nm one billionth of a metre

Nanoparticles

Nanotubes like this could be used to make tiny mechanical devices, molecular computers or extremely strong materials

Some uses of nanoparticles

Special properties

Nanoparticles are so small that they have different properties than the same substance in normal-sized pieces. For example, pieces of gold are, fairly obviously, gold-coloured. But gold nanoparticles are deep red or even black when mixed with water. Such different properties are very useful.

Some uses

Titanium dioxide is a white solid used in house paint and certain candy-coated chocolates. Titanium dioxide nanoparticles are so small that they do not reflect visible light, so they cannot be seen. They are used in sunblock creams because they block harmful ultraviolet light from the Sun without appearing white on the skin.

Some cosmetics contain 'liposomes', which are fatty nanoparticles. Liposomes also have great potential in the pharmaceutical industry, as they can deliver tiny doses of medicines direct to cells.

Some worries

Since the properties of a given nanoparticle are not easily predicted by studying the substance from which it is made, there are worries that nanoparticles may have undiscovered side-effects.

Nanoparticles have a very large surface area compared to their volume, so they are often able to react very quickly. This makes them useful as catalysts to speed up reactions. For example, they can be used in self-cleaning ovens and windows. However, there is also the possibility that they might speed up reactions in living things in unpredictable ways, perhaps causing illness or death