Nanoparticles, Materials and Composites

What Are Nanoparticles?

Nanoparticles are structures that measure between 1 and 100 nanometres (nm) in at least one dimension. One nanometre is 10^-9 m — far smaller than a human hair (~80 000 nm wide). By comparison, fine particles (used in older applications such as talcum powder) are typically 100 nm–2500 nm, and bulk materials are larger still.

Nanoparticles are not a new phenomenon: soot from candles and carbon black in ancient ink contain nanoparticles. What is new is the ability to engineer them precisely and exploit their unusual properties.

Surface Area to Volume Ratio

The key reason nanoparticles behave differently from bulk materials is their very high surface area to volume ratio. As a particle is made smaller, the proportion of atoms on the surface compared to those in the interior increases dramatically. Surface atoms are more reactive because they have unsatisfied bonds — so a higher surface area to volume ratio means greater chemical reactivity.

Imagine cutting a large cube into tiny cubes: the total surface area increases while the total volume stays the same. This principle is why nanoparticles of gold, silver, and titanium dioxide behave very differently from the same substances in their visible (bulk) forms.

Applications of Nanoparticles

Nanoparticles are exploited across many fields because of their enhanced properties:

• Sunscreen: titanium dioxide and zinc oxide nanoparticles absorb and scatter ultraviolet radiation more effectively than bulk particles of the same materials. Their tiny size also makes them transparent on skin rather than leaving a white film.
• Medicine: nanoparticles can be engineered to carry drugs directly to cancer cells, reducing side effects compared with conventional chemotherapy. Silver nanoparticles have antimicrobial properties and are incorporated into wound dressings and clothing.
• Electronics: nanoparticles enable smaller, faster components. Carbon nanotubes have very high tensile strength and electrical conductivity, making them valuable in advanced electronics and structural materials.
• Catalysis: nanoparticle catalysts (e.g. platinum nanoparticles in catalytic converters) provide a much larger surface area for reactions to occur, improving efficiency.

Risks and the Precautionary Principle

The same properties that make nanoparticles useful also raise concerns. Their tiny size means they can penetrate biological barriers — entering cells, crossing the blood–brain barrier, or accumulating in organs — in ways that larger particles of the same material cannot. The long-term health effects are still being researched, and some nanoparticles have been shown to cause inflammation or cellular damage in laboratory studies.

Because the full risks are not yet understood, scientists and regulators apply the precautionary principle: taking protective measures before harms are proven, rather than waiting for certainty. This means using nanoparticles only where benefits clearly outweigh the risks, and continuing active research.

Properties of Glass and Ceramics

Soda glass is made by melting silicon dioxide (sand) with sodium carbonate and limestone. It is transparent, hard, and chemically resistant, but brittle and has a relatively low melting point. Borosilicate glass contains boron trioxide, giving it a much higher melting point and resistance to thermal shock — it is used in laboratory glassware and ovenproof dishes.

Clay ceramics such as pottery and bricks are made by shaping clay and firing it at high temperatures. They are very hard, brittle, and chemically inert. Their crystalline structure makes them good thermal and electrical insulators.

Metals, Alloys and Composites

Pure metals have regular, closely packed crystal structures, allowing layers of atoms to slide over each other — making them malleable. Adding another element creates an alloy, where the different-sized atoms disrupt the regular layers, making it harder for them to slide. This is why alloys are generally stronger and harder than pure metals. Steel (iron + carbon), brass (copper + zinc), and bronze (copper + tin) are common examples.

A composite material combines materials so that each contributes its best property. Glass-fibre-reinforced polymer (GFRP, or fibreglass) combines glass fibres (stiff and strong) embedded in a polymer resin (lightweight). Carbon-fibre-reinforced polymer (CFRP) uses carbon fibres, giving even higher stiffness and strength at low mass. Both are used in sports equipment, aircraft bodies, and boat hulls where a high strength-to-weight ratio is needed.