# Nanotechnology

is the use and control of very small structures that are 1 to 100 nanometres in size.

The small size of means that it is possible that they can penetrate into the body. This could bring medical benefits but it could also be a risk to human health.

Nanotechnology does bring possible risks to both the environment and human health. Many of these risks are not yet fully known. Money has been invested into researching the uses of nanoparticles. It will take time and more money to fully research the risks, including the effect of nanoparticles on the human body.

Judgements on whether to use nanotechnology relies on balancing the benefits against the possible risks.

## Key properties

Nanoparticles have distinctive properties, including:

• very small size
• high surface area to volume ratios

## Properties and uses

### Very small size

Nanoparticles are so small that they can enter biological tissue.

They can be mixed into other materials to form with improved properties.

Nanoparticulate materials are used in some paints, cosmetics and sunscreens. Sunscreens block harmful from the sun reaching the skin. Zinc oxide blocks ultraviolet light, so it is used in sunscreens. Bulk zinc oxide is white, but nanoparticulate zinc oxide cannot be seen when it is spread on the skin. Many people prefer nanoparticulate sunscreen because it is not obvious that they are wearing it.

Nanoparticles of silver are added to a special type of sock. These silver nanoparticles kill the bacteria that lead to smelly feet.

### High surface area to volume ratios

speed up reactions. The reactions take place on the surface of the catalyst. The greater the surface area of the catalyst compared with the volume of the catalyst, the more effective the catalyst will be at speeding up the reaction.

Nanoparticles have a very high surface area to volume ratio and make excellent catalysts.

Self-cleaning window panes have nanoparticulate coatings. When light hits these coatings, they break down dirt on the glass.

### Example

Question

A cube has a side length of 10 nm. Calculate its surface area to volume ratio.

The surface area of 1 face = 10 × 10 = 100 nm

The cube has 6 faces

The total surface area of the cube = 6 × 100 = 600 nm2

The volume = 10 × 10 × 10 = 1,000 nm3

Surface area to volume ratio = $$\frac{600}{1000}$$

= 0.6

Question

A cube has edges of length 2 nm. Calculate its surface area to volume ratio.

How does this compare with the larger cube?

Surface area of 1 face = 2 × 2 = 4 nm2

Total surface area of cube = 6 × 4 = 24 nm2

Volume = 2 × 2 × 2 = 8 nm3

Surface area to volume ratio = $$\frac{24}{8}$$

= 3

The surface area to volume ratio is greater than the ratio for the larger cube.