C. Structure and Properties of Matter · Structure and Properties of MatterMaterials by Design: Kevlar, Composites, Superconductors and Nanomaterials
C1 C2.5 A1.9About 70 minutes
Learning goals- I can explain how the structure and bonding of specialized materials give them their useful properties.
- I can describe uses of Kevlar, composites, superglue, superconductors, nanomaterials and optical fibres.
- I can evaluate the benefits and environmental impact of a material using life-cycle thinking.
- I can propose ways to reduce the environmental impact of a product.
Words to know
polymer
A large molecule made of many repeating units (monomers) joined by covalent bonds.
composite
A material made of two or more different materials combined to give improved properties.
superconductor
A material that has zero electrical resistance below its critical temperature.
critical temperature
The temperature below which a material becomes superconducting.
nanomaterial
A material with at least one dimension between about 1 and 100 nm.
life-cycle assessment
An evaluation of a product's environmental impact from raw materials to disposal.
Materials made to order
The bulletproof vest of a police officer, the carbon-fibre hockey stick of a Canadian Olympian, the optical fibre carrying this lesson to your screen, and the superconducting magnet in an MRI scanner were all designed using knowledge of structure and bonding. Materials science asks: if we arrange atoms and bonds in a certain way, what properties will we get?
In this lesson you will explain how the structures of some specialized materials give them their properties, and evaluate their benefits to society and their environmental impact.
Kevlar
Kevlar was invented in 1965 by Stephanie Kwolek, a chemist at the DuPont company. It is a polymer (a polyamide, related to nylon) whose chains contain flat benzene rings, which make them rigid and straight. When the polymer is spun into fibres, the chains line up side by side, and the N–H group of one chain forms hydrogen bonds with the C=O group of the next. Millions of these hydrogen bonds plus the strong covalent chains make fibres that are several times stronger than steel of the same mass, heat-resistant and light.
Uses: protective vests and helmets, cut-resistant gloves, firefighters' gear, tires, ropes, sports equipment. Environmental issues: made from petroleum-based chemicals with energy-intensive processing; very durable and hard to recycle or break down, so worn-out items usually go to landfill.
Polymer composites
A composite combines two materials to get the best of both. Carbon-fibre reinforced polymer embeds strong, stiff carbon fibres (graphite-like sheets running along each fibre) in a tough plastic resin. It is used in aircraft such as the Boeing 787, whose structure is about half composites by weight, as well as in bicycles, hockey sticks and wind-turbine blades. Lighter aircraft burn less fuel. Environmental issues: making carbon fibre takes a lot of energy, and because the fibres and resin are bonded together, composites are hard to recycle; researchers are developing ways to recover the fibres.
Superglue
Cyanoacrylate glue is a small molecule with a C=C double bond and polar groups. Traces of water on almost any surface start a rapid addition polymerization (the double bonds open and link into long chains), so the glue sets in seconds. Medical versions are used to close some cuts. Issues: it bonds skin instantly, so it needs careful handling, and its vapour can irritate eyes.
Superconductors
A superconductor carries electric current with zero resistance below a critical temperature. Ordinary superconducting metals and alloys (such as the niobium-titanium in MRI magnets) must be cooled with liquid helium (about 4 K, −269 °C). In 1986 to 1987 scientists discovered ceramic superconductors such as YBCO (yttrium barium copper oxide), which superconduct below about 93 K, so they can be cooled with much cheaper liquid nitrogen (77 K, −196 °C).
Uses: MRI magnets, particle accelerators, some experimental magnetic-levitation trains, and power cables that lose no energy as heat. Issues: cooling costs and energy, helium scarcity, and ceramics that are brittle and hard to make into wires.
Nanomaterials
A nanomaterial has at least one dimension between about 1 and 100 nanometres. At this scale, properties can change because so many atoms are at the surface.
- Graphene, a single layer of graphite, is extremely strong for its thickness and conducts electricity very well. Andre Geim and Konstantin Novoselov isolated it in 2004 using sticky tape, and won the 2010 Nobel Prize in Physics.
- Carbon nanotubes are graphene sheets rolled into tubes, being developed for strong, light materials and electronics.
- Nanoparticles of titanium dioxide and zinc oxide in sunscreens block UV light while looking clear on the skin, and silver nanoparticles in some fabrics kill bacteria that cause odours.
Issues: scientists are still studying how nanoparticles behave in the environment and in the body. For example, silver nanoparticles washed out of clothing can reach wastewater and may harm beneficial microorganisms. Health Canada and other regulators are developing rules for nanomaterials.
Optical fibres
An optical fibre is a thread of very pure silica glass (SiO₂, an amorphous covalent network) that carries light by total internal reflection. Fibres carry internet and phone signals over huge distances with little loss, and use far less copper (a mined metal) than electrical cables. They are hard to recycle, but last for decades.
Evaluating a material: life-cycle thinking
To judge a material's overall impact, scientists use a life-cycle assessment: consider every stage from raw materials (mining, petroleum), manufacturing (energy, waste, emissions), use (benefits, safety, energy saved) to end of life (reuse, recycling, landfill, pollution). A material can be both helpful and harmful; a good evaluation weighs both and suggests ways to reduce the harm (designing for recycling, using renewable energy in manufacturing, safe disposal).
Worked exampleExample 1: Structure explains a property
Explain, using bonding, why Kevlar fibres are so strong while a bag of Kevlar powder (unaligned chains) would not be.
- Strength along a fibre comes from the covalent bonds in each chain and the hydrogen bonds between neighbouring chains.
- In a fibre, rigid chains are aligned, so each chain forms many hydrogen bonds with its neighbours along its whole length, and a load is shared by many chains.
- In a powder, chains are randomly arranged, with few contacts between them, so the particles separate easily.
The fibre's strength depends on chain alignment, which allows a huge number of hydrogen bonds between chains.
Worked exampleExample 2: Why liquid nitrogen matters
Convert the critical temperature of YBCO (93 K) and the boiling point of liquid nitrogen (77 K) to °C, and explain why this discovery was important.
- °C = K − 273: 93 K = −180 °C; 77 K = −196 °C.
- Liquid nitrogen is colder than YBCO's critical temperature, so it can keep YBCO superconducting.
- Liquid nitrogen is made from air and is far cheaper and more plentiful than liquid helium (needed for older superconductors near 4 K).
93 K = −180 °C, 77 K = −196 °C. Cheap liquid-nitrogen cooling made practical superconductor applications much more affordable.
Worked exampleExample 3: A balanced evaluation
Evaluate silver-nanoparticle anti-odour socks in three sentences.
- Benefit: silver nanoparticles kill odour-causing bacteria, so the socks can be washed less often, saving water and energy.
- Cost: some nanoparticles wash out into wastewater and may harm beneficial bacteria at treatment plants or in rivers; long-term effects are still being studied.
- Judgement: the benefit is modest (comfort) compared with an uncertain environmental risk, so ordinary socks washed normally may be the more responsible choice.
A strong evaluation names a specific benefit, a specific risk and a justified judgement.
Just for funSuperglue was discovered by accident, twice. In 1942 Harry Coover was trying to make clear plastic gun sights, and the cyanoacrylates he made stuck to everything, so he rejected them. In 1951 he met them again while working on heat-resistant aircraft canopies, realized "sticks to everything" might be a feature, not a bug, and superglue went on sale in 1958.
Hands-on activityLife-cycle assessment of an everyday product
You need: an everyday product made from a specialized material, such as a hockey stick (carbon fibre or wood), a bicycle helmet, a phone screen, a fleece jacket, a sunscreen bottle or a non-stick pan; paper and pencil; internet or library access for a little research.
- Draw a four-box flowchart: Raw materials → Manufacturing → Use → End of life.
- In each box, write what you know or can find out: the materials and where they come from, energy and waste in production, benefits and risks during use, and what happens when it is thrown away.
- Identify the structure-property link: which bonding or structure gives the product its key property? (Example: a composite stick is stiff and light because of aligned carbon fibres in resin.)
- Score each stage from 1 (low impact) to 5 (high impact) and justify each score in one sentence.
- Propose two realistic ways to reduce the product's environmental impact (for example, buy used, choose a recyclable alternative, extend its life, return it to a take-back program).
What to look for: a thoughtful assessment links structure to property, gives specific impacts at each stage rather than general statements, and suggests realistic actions. There is no single right score; the reasoning is what matters.
Your turn
1What two types of bonding give Kevlar fibres their strength?
Covalent bonds along each polymer chain and hydrogen bonds between neighbouring chains.
2What is a superconductor?
A material with zero electrical resistance below its critical temperature.
3Why was the discovery of YBCO important?
It superconducts below about 93 K, above the boiling point of liquid nitrogen (77 K), so it can be cooled cheaply instead of with liquid helium.
4What makes superglue set so quickly?
Traces of water start a rapid addition polymerization of the cyanoacrylate molecules.
5Define a nanomaterial and give one example.
A material with at least one dimension of about 1 to 100 nm; e.g., graphene, carbon nanotubes, TiO₂ or ZnO nanoparticles in sunscreen.
6Give one benefit and one environmental drawback of carbon-fibre composites in aircraft.
Benefit: lighter planes burn less fuel. Drawback: energy-intensive to make and hard to recycle.
7What type of solid is the glass in an optical fibre?
A covalent network of silicon and oxygen (amorphous SiO₂).
More practice: warm-up
Stephanie Kwolek (DuPont, 1965).
A material made by combining two or more materials to get better properties.
3At what temperature does liquid nitrogen boil, in kelvins?
5What are the four stages of a life-cycle assessment?
Raw materials, manufacturing, use, end of life.
More practice: on your own
1Explain why graphene conducts electricity, using hybridization.
Each carbon is sp² and bonded to three others; the fourth electron of each carbon is in an unhybridized p orbital, forming a delocalized π system across the sheet, so electrons move freely.
2Why do MRI scanners use superconducting magnets, and what is the trade-off?
Superconducting coils carry huge currents with no resistance, producing very strong steady fields without heat losses. The trade-off is the cost and supply of liquid helium for cooling.
3Give one benefit and one concern about zinc oxide nanoparticles in sunscreen.
Benefit: block UV while appearing clear, encouraging sunscreen use. Concern: possible effects of nanoparticles washing into lakes and oceans are still being studied.
4Suggest two ways to reduce the environmental impact of worn-out Kevlar vests.
Any two: recycle the fibres into lower-grade products (for example, as reinforcement or padding), design vests to be taken apart for recycling, extend service life where safe, return to take-back programs.
5Why is a composite hockey stick both stiff and light?
Aligned carbon fibres (strong covalent sheets along each fibre) carry the load, while a lightweight polymer resin holds them in place; the combination is stiffer and lighter than wood of the same strength.
Challenge
1A copper power cable loses about 5% of the energy it carries as heat. Explain why superconducting cables would remove this loss, and suggest why they are not yet used everywhere.
Heat loss in a wire comes from electrical resistance (P = I²R). A superconductor has R = 0, so no energy is lost as heat. They are not used everywhere because they must be kept below their critical temperature (cooling equipment and energy cost), the ceramics are brittle and hard to make into long wires, and installation is expensive.
2Kevlar and nylon are both polyamides. Kevlar's chains contain benzene rings; nylon's chains are flexible chains of CH₂ groups. Predict which is stiffer and explain.
Kevlar: benzene rings and amide groups make its chains rigid and straight, so they line up and form regular hydrogen bonds along their length. Nylon's flexible CH₂ chains can bend and coil, so they align less perfectly and the fibre is more stretchy.
3Write a short evaluation (3 to 5 sentences) of this claim: "Nanomaterials should be banned until they are proven completely safe."
Sample answer: No technology can be proven completely safe, so the standard is unrealistic. Nanomaterials give real benefits, such as clear UV-blocking sunscreens that reduce skin-cancer risk and stronger, lighter materials that save fuel. However, their environmental and health effects are not fully known, so they should be tested and regulated case by case, with labelling and limits on uses where nanoparticles are released easily (such as washing out of clothing). A precautionary, evidence-based approach is better than a blanket ban. (Look for a clear position, benefits and risks, and a reasoned conclusion.)
Quiz
1. What causes Kevlar's exceptional strength?
2. Below its critical temperature, a superconductor has:
3. Why are ceramic superconductors like YBCO cheaper to use than older ones?
5. Which is a major environmental challenge for carbon-fibre composites?
6. Which stage of a life-cycle assessment considers what happens when a product is thrown away?
Big idea (C1): knowledge of structure and bonding lets scientists design materials with specific properties, and every material should be judged on both its benefits and its environmental impact over its whole life cycle.
How to help: the life-cycle activity works with almost any household object. Encourage your teen to research from reliable sources and to give specific, justified judgements rather than "good" or "bad".
Common difficulties:
- Describing uses without linking them to structure and bonding.
- One-sided evaluations (all benefits or all harms).
- Confusing kelvin and Celsius (°C = K − 273).