Nanoparticles and Polymers
Nanoparticles
Nanoparticles are particles that have dimensions between 1 and 100 nanometres (nm). A nanometre is one billionth of a metre (1 nm = 1 × 10⁻⁹ m, or 0.000000001 m).
For comparison:
- A typical atom is about 0.1–0.3 nm across
- Nanoparticles contain a few hundred to a few thousand atoms
- Fine particles (dust) are 100–2500 nm (1 × 10⁻⁴ to 2.5 × 10⁻³ mm)
- Coarse particles (PM₁₀) are 2500–10000 nm
Surface Area to Volume Ratio
As particles get smaller, their surface area to volume ratio increases dramatically. This is the key property that makes nanoparticles special.
A cube of side 1 cm has:
- Surface area = 6 cm²
- Volume = 1 cm³
- SA:V = 6:1
If that same volume is divided into nano-sized cubes, the total surface area becomes enormously larger while the total volume stays the same.
This high surface area to volume ratio means nanoparticles have different properties from the same material in bulk, including:
- Different colours — gold nanoparticles can appear red or purple
- Higher reactivity — more surface atoms available for reactions
- Better catalytic activity — more surface sites
- Different electrical properties
Uses of Nanoparticles
| Application | Nanoparticle | Why |
|---|---|---|
| Sunscreen | Titanium dioxide | Absorbs UV, transparent (not white) |
| Medicine | Silver | Antibacterial coatings on wounds |
| Drug delivery | Various | Can carry drugs to specific cells |
| Catalysts | Metal nanoparticles | High surface area, less material needed |
| Electronics | Carbon nanotubes | Conduct electricity, tiny circuits |
| Self-cleaning glass | Titanium dioxide | Breaks down dirt in sunlight |
| Deodorants | Silver | Kills bacteria causing odour |
Concerns About Nanoparticles
Because nanoparticles are a relatively new technology, there are concerns about their safety:
- Health effects are not fully understood — they are small enough to enter cells and even cross the blood-brain barrier
- They may be toxic in ways that the bulk material is not
- Environmental impact is unknown — they could accumulate in ecosystems
- Workers manufacturing nanoparticles may face inhalation risks
- More research is needed before we fully understand the long-term risks
Polymers
Polymers are very large molecules made by joining many small molecules called monomers together in a repeating chain.
The word comes from Greek: poly (many) + mer (part).
Structure of Polymers
A polymer chain can contain thousands or even millions of monomer units. The properties of a polymer depend on:
- What monomer it is made from
- The length of the chains
- The forces between chains (intermolecular forces)
- Whether the chains are cross-linked
Types of Polymers (Overview)
There are two main types of polymerisation (covered in detail in the Organic Chemistry topic):
1. Addition polymerisation — alkene monomers join together; no other product formed
2. Condensation polymerisation — monomers join with the loss of a small molecule (usually water)
Properties and Uses
| Polymer | Monomer | Use | Properties |
|---|---|---|---|
| Poly(ethene) — polyethylene | Ethene | Plastic bags, bottles | Flexible, waterproof |
| Poly(propene) — polypropylene | Propene | Crates, ropes | Strong, rigid |
| Poly(chloroethene) — PVC | Chloroethene | Window frames, pipes | Rigid, durable |
| Poly(tetrafluoroethene) — PTFE | Tetrafluoroethene | Non-stick coatings | Very low friction |
Thermosoftening and Thermosetting Polymers
Thermosoftening polymers (thermoplastics):
- Soften and melt when heated, harden when cooled
- Can be remoulded repeatedly
- Polymer chains are held together by weak intermolecular forces that are easily overcome by heating
- Examples: poly(ethene), PVC, polystyrene
Thermosetting polymers (thermosets):
- Do not soften when heated — they char and decompose
- Cannot be remoulded
- Polymer chains are held together by strong covalent cross-links between chains
- These cross-links cannot be broken without destroying the polymer
- Examples: Bakelite, melamine, epoxy resins
Disposing of Polymers
Most polymers are not biodegradable — they are not broken down by microorganisms. This causes environmental problems:
- They fill up landfill sites
- If burned (incineration), they can release toxic gases (e.g. hydrogen chloride from PVC)
- They can harm wildlife if they enter the environment
Solutions include:
- Recycling — sorting and reprocessing thermosoftening polymers
- Developing biodegradable polymers — made from plant-based materials like starch
- Reducing use — using alternatives or less packaging
Exam Tips
- Know the size range for nanoparticles: 1–100 nm
- Be able to explain why nanoparticles have different properties: high surface area to volume ratio
- Understand the difference between thermosoftening and thermosetting in terms of bonding between chains
- Be able to discuss both benefits and risks of nanoparticles — a balanced answer is needed for 6-mark questions