C2 - Material Choices

C2 - Material Choices

1. Properties

   • Properties are the characteristics a material has. For example...
     • Density - mass per unit volume. Eg. g/cm3
     • Stiffness - a material that is good at not bending when force is applied.
     • Strength - how good a material is at resisting a force.
     • Hardness - how difficult a material is to cut in to.

2. Polymers

   • Polymer molecules are very, very long chains of atoms.
   • They can be natural and synthetic.
     • Natural polymers include wool, cotton, silk, rubber, fur and paper.
     • Synthetic polymers include polythene, PVC and polypropylene.
   • We use polymers for our basic needs - physical, bodily, social/emotional and needs of the mind.
   • Polymerisation is the process of making polymers.
   • A monomer is the smallest unit that joins to make a polymer.
     • AA polymer - repeating monomers.
     • AB polymer - two different monomers.
   • Longer chains of molecules, eg. polythene, are harder to break.
   • Shorter chains of molecules, eg. candles, are weaker.
   • In some polymers, the chains are jumbled, and are in a very irregular arrangement.
   • In some polymers, the chains are in neat lines. These are called crystalline polymers.
   • Changing the properties of polymers.
     • By increasing the crystallinity of polymers, it makes them stronger and denser.
       • The molecules will be closer together, meaning they are harder to seperate.
     • Vulcanisers can be used with rubber. These set up crosslinks which make the polymer more stiff and less flexible.
     • Plasticisiers are oily liquids that set up small molecules between the chains.
       • The chains are therefore further apart, and so less energy is needed to break them, and the polymer is more flexible.

3. We make items from all sorts of materials, like metals, polymers, ceramics and rocks.

4. Intermolecular forces are the forces between molecules.

   • The larger the molecule, the larger the intermolecular forces.

5. Hydrocarbons.

   • Hydrocarbons are substances made from only hydrogen and carbon.
     • Diesel contains hydrocarbons with longer chains.
     • Petrol has hydrocarbons with eight carbons.
     • Crude oil is a mix of hydrocarbons.
       • Over millions of years, high temperatures and pressure turns it in to crude oil.
       • Crude oil is useless straight from the ground, but it can be separated.
         • Fractional distillation.
           • This is the process of separating hydrocarbons in to groups with different boiling points. Hydrocarbons with similar lengths have similar boiling points.
           • Longer chains - bitumen (road surfaces) and lubricating oil.
           • Shorter chains - refinery gas and petrol.

6. Nanotechnology

   • The use and control of structures called nanoparticles.
   • Each nanometer is a billionth of a metre.
   • Nanoparticles are used in sports, because they are stronger and lighter.
   • Nanoparticles also have antibacterial properties.
   • We do not know the full effect of nanoparticles on health.