9d Flashcards
The size of nanoparticles
Tiny particles are often measured in nanometres (nm) or micrometres (µm).
1 nanometre (nm) = 1 x 10^-9 m
1 micrometre (um) = 1 x 10^-6 m
Nanoparticles are really tiny particles that have diameters between 1 nm and 100 nm. Nanoparticles contain only a few hundred atoms. A typical atom has a diameter of about 0.1 nm and small molecules generally have diameters less than 1 nm, so nanoparticles are between about 10 and 1000 times bigger across than single atoms and up to 100 times bigger than small molecules.
Surface area of nanoparticles
Nanoparticles have a very high surface area to volume ratio the surface area is very large compared to the volume. this means
surface area to volume ratio = surface area : volume
As particles decrease in size, the size of their surface area increases in relation to their volume assuming they stay a similar shape. This causes the surface area to volume ratio to increase. Cubes are a simple way to show that this is true as their side length decreases by a factor of 10, the surface area to volume ratio always increases by a factor of 10.
Uses of nanoparticles
Nanoscience is the study of nanoparticles and is becoming an increasingly advanced area of science. Scientists are always trying to find new ways to use nanoparticles. The particular properties of a nanoparticle will decide what it can be used for. Below are some applications that nanoparticles are already being used for.
As catalysts
Because reactions take place on the surface of catalysts, the bigger the surface area, the more collisions there will be and so the faster the rate of reaction. Nanoparticles have a high surface area to volume ratio, so they can make good catalysts.
Platinum is typically used as the catalyst in fuels cells. It’s really expensive, but because platinum nanoparticles have a huge surface area to volume ratio, only a tiny quantity of them are needed. Alternatively, other types of nanoparticles can be used instead of the expensive platinum
In nanomedicine
This is a hot topic. The idea is that tiny particles (such as fullerenes see page 63) are absorbed more easily by the body than most particles. This means they could deliver drugs right into the cells where they’re needed.
In electronics
Some nanoparticles conduct electricity, so they can be used in electronics. For example, they can be used to make really thin, light display screens for devices or really tiny memory chips that hold a vast amount of data.
In sunscreens
Nanoparticles are being used in sunscreen as they have been shown to be better than the materials in traditional sunscreens at protecting skin from harmful UV rays. They also give better skin coverage than traditional sunscreens and don’t leave white marks on the skin.
In deodorants
Silver nanoparticles are added to some deodorants as they have antibacterial properties.
In cosmetics
Nanoparticles are being used in cosmetics. For example, they’re used to improve moisturisers without making them really oily, and to deliver active ingredients to lower layers of skin in anti-aging creams.
In sports equipment
Nanoparticles are added to materials used in sports equipment, e.g. tennis rackets, golf clubs and golf balls. They can make the material much stronger and more durable.
Disadvantages of nanoparticles
It’s not yet clear whether the nanoparticles from sunscreens can get into your body and, if they do, whether they might damage cells. The same risks exist with cosmetics and deodorants that contain nanoparticles. Nanoparticles in sun creams may also have damaging effects if they’re washed away into the environment.
When antibacterial fabric is washed, some of the silver nanoparticles end up in the waste water. They don’t degrade and so end up in rivers. Some studies have shown that silver nanoparticles can be toxic to fish.
Some nanoparticles used in medicine don’t break down easily so they could start to build up in cells. They could also cause problems such as lung inflammation if they’re breathed in.
Polymers
Polymers are very large molecules formed when many small molecules, called monomers, join together. Strong covalent bonds hold the atoms together in long chains
Most polymers are insulators of heat and electricity, they can be flexible (they can be bent without breaking) and are easily moulded. They’re often cheaper than most other materials, and they also tend to be less dense than most metals or ceramics, so are often used for products that need to have a low mass.
There are lots of different monomers that can be used to make polymers. This means that the properties of different polymers are varied resulting in loads of applications.
Ceramics
Ceramics are non-metallic solids with high melting points that aren’t made from carbon-based compounds.
Ceramics are excellent insulators of heat and electricity. They tend to be very brittle (not very flexible and break easily) and stiff, but also strong and hardwearing. They don’t degrade or corrode like other materials can, so they can last a lot longer.
Example - Porcelain plates or bowls are excellent at insulating heat. This is why you can carry hot food in them without hurting your hand. However, porcelain shatters easily if dropped, as it’s brittle
Examples of the uses of polymers
Polyesters are used in clothing due to their ability to stretch and dry quickly making them an ideal substitute for cotton in clothing such as t-shirts.
High-density poly(ethene) is used to make water pipes as it’s strong and rigid.
Light, stretchy polymers such as low-density poly(ethene) are used for plastic bags and squeezy bottles.
Poly(styrene) foam is used in packaging to protect breakable things, and as a thermal insulator.
Heat-resistant polymers such as melamine resin and poly(propene) are used to make plastic kettles.
Polymers can degrade and break down over time, so polymer products don’t always last as long as those made from other materials.
- Clay ceramics
Clay is a mineral formed from weathered and decomposed rock. It’s a soft material when by it’s dug out of the ground, so it can be moulded into different shapes. When it’s fired at high temperatures, it hardens to form a clay ceramic.
As clay can be moulded when wet and then be hardened, it’s ideal for making pottery and bricks. As clay bricks are hard they can withstand the weight of lots more bricks on top of them.
Composites
Composites are made of one material embedded in another. Fibres or fragments of a material (known as the reinforcement) are surrounded by a matrix acting as a binder.
The properties of composites depend on the matrix/binder and the reinforcement used to make them, so they have many different uses.
