2.4 Bulk and surface properties of matter including nanoparticles

2.4 Bulk and surface properties of matter including nanoparticles

2.4.1 Sizes of particles and their properties

- Nanoparticles are structures that are 1–100 nm in size, of the order of a few hundred atoms.
- They are smaller than fine particles (PM2.5). Fine particles are particles with diameters between 100 and 2500 nm, and are commonly referred to as "particulates" in a pollution context.
- Coarse particles (PM10) have diameters between 1 × 10-5 m and 2.5 × 10-6 m. Coarse particles are often referred to as dust.

Comparison of particle sizes

Type of Particle Typical Size Range Example / Context
Nanoparticles 1 – 100 nm Medicines, catalysts, sunscreen
Fine Particles (PM2.5) 100 – 2500 nm (0.1 – 2.5 μm) Air pollution particulates
Coarse Particles (PM10) 2.5 – 10 μm (2.5 × 10-6 m to 1 × 10-5 m) Dust, pollen

Surface area to volume ratio

- The surface area to volume ratio (SA:V) becomes larger as the size of the particle decreases.
- For a cube of side length L:

This means that nanoparticles, being extremely small, have a much greater SA:V ratio compared to bulk material. A large surface area relative to volume makes them highly reactive and useful for applications such as:

Worked example: SA:V for cubes at different scales

Object Side length, L (m) Surface area, 6L2 (m2) Volume, L3 (m3) SA:V, 6/L (m-1)
1 cm cube 1.0 × 10-2 6.0 × 10-4 1.0 × 10-6 6.0 × 102
10 nm cube 1.0 × 10-8 6.0 × 10-16 1.0 × 10-24 6.0 × 108

Moving from a 1 cm cube to a 10 nm cube increases SA:V by a factor of 106 (one million), because SA:V scales as 1/ L.


2.4.2 Uses of nanoparticles

- Nanoparticles have many applications in medicine, in electronics, in cosmetics and sun creams, as deodorants, and as catalysts.
- New applications of nanoparticles is an important area of research.

Advantages and disadvantages of nanoparticles

Advantages Disadvantages
  • Useful in medicine (e.g. targeted drug delivery, tumour treatment).
  • High surface area to volume ratio → very effective as catalysts.
  • Transparent coatings (e.g. in suncreams, self-cleaning glass).
  • Can improve strength, durability and functionality of materials (e.g. clothing, sports equipment).
  • Potentially toxic to humans and the environment (can enter cells easily).
  • Uncertain long-term health effects due to their small size and reactivity.
  • Expensive and difficult to manufacture in bulk.
  • Some may bopaccumulate in the environment if not disposed of properly.