C2: Material choices

Important properties include:

• Melting point
• Strength in tension
• Strength in compression
• Stiffness 
• Hardness 
• Durability

The effectiveness and durability of a product depends on the properties of its materials. A product that is durable lasts for a long time before breaking or rotting.

• Crude oil is mainly a mix of hydrocarbon molecules of different lengths.
• Hydrocarbon molecules are made from hydrogen and carbon only.

• Fractional distillation is carried out to separate crude oil into fractions.
• Fraction - Mixture of hydrocarbon molecules with similar boiling points.
• Crude oil is heated in a furnace, Its coumpounds evaporate and become gases.
• The gases enter the tower, as they move up, they cool down.
• Different fractions condense at different levels:
• Compounds with small molecules have low boiling points, the forces between the molecules are weak, little energy is needed for them to break.
• Compounds with bigger molecule have higher boiling points.
• Different fractions have different uses: Fuel, Lubricants, Raw materials to make new materials in chemical synthesis.

• Polymers- Very long molecules made up of small molecules (Monomers).
• Polymerisation- When Monomers join together to form Polymers.

• Their properties depend on how their molecules are arranged and held together.

Wax has shorter molecules than polythene. This means that:

• Polythene is stronger- its molecules are tangled and difficult to separate.
• Polythene melts at higher temperatures- there are stronger forces between long polythene molecules than between shorter wax molecules.

• Making chains longer - Makes it stronger.
• Adding cross-links - Makes it Harder, Stronger, Less flexible.
• Adding Plasticisers - Makes it Softer, More Flexible.
• Increasing Crystallinity by lining up polymer molecules - Makes it Stronger, Denser.

• Nanotechnology- the use and control of tiny structures.
• Nanoparticles are about 1-100 nanomertres across.
• They have different properties compared with larger particles of the same material.
• Nanoparticles have bigger surface area compared to their volume.
• Nanoparticles can occur:

-Naturally, in sea spray.

-By design:

Silver nanoparticles give fibres antibacterial properties, in medical dressings.

Adding nanoparticles to plastics for sports equipment such as tennis rackets make them stronger.

Nanoparticles may have harmful effects on health. Some think these effects should be studied more closely before using more nanoparticles.