Strength in nanos

If a medieval foot-soldier were to meet a modern infantryman, both might find themselves envious of the other’s equipment.

An Agincourt soldier, for instance, would find his 21st century counterpart’s weaponry and communications equipment beyond comprehension. But today’s infantryman might look at his predecessor’s chain mail shirt and padded jerkin and wonder: ‘is his armour actually better than mine?’

Protecting soldiers from bullets and shrapnel is a difficult and controversial problem. A CCLRC Daresbury Laboratory team, led by Dr Vin Dhanak, is involved in a project which hopes to solve it. Working in collaboration with materials scientists from Tuskegee and Florida Atlantic universities, Dhanak is investigating how and why some nanoparticles can greatly increase the strength of polymer fibres.

‘Soldiers in Iraq and Afghanistan are receiving terrible limb injuries because their body armour only protects their torsos; they have virtually no protection on their arms and legs,’ said Dhanak. ‘Our ultimate goal is to develop a nanocomposite fibre than can be woven into a lightweight fabric that can withstand the impact of bullets.’

The US researchers are infusing nanomaterials, such as silicon or titanium dioxides or carbon nanotubes, into polymers such as nylon or polypropylene. These mixtures are then melted and spun, and the resulting fibres subjected to tests of properties such as tensile strength and ballistic resilience.

‘These materials can resist bullets, but we don’t understand why,’ said Dhanak. ‘If we knew what was going on, we might be able to design production processes to optimise these properties and make the materials even stronger.’

Dhanak’s team is using the synchrotron light source and photoelectron spectrometer at Daresbury to study the interaction between the nanoparticles and the host materials, looking for clues about the bonding between the components. ‘Our job is to look at how the nanoparticles bond inside the matrix, to understand its electronic structure,’ he said.

‘For example, we know that nanotubes have structural defects, and these seem to be very important for molecules like nylon to attach itself to the nanotube.’ This could help in tailoring the nanomaterial component so that it had more attachment sites — which could increase the strength of the composite.

Other factors contributing to composite strength could be the way the nanomaterials are aligned. ‘It’s thought that nanotubes are aligned in a particular direction, but we don’t know that. If it turns out to be true, we could devise a process to see how we can improve the alignment, or see if alignment in a different direction could improve things even more.’

The team has already established that impurities in the composite can have a considerable weakening effect. Left-over catalysts from production of nanotubes are difficult to remove from the composite, said Dhanak, so the team is now using higher-purity materials.

The project’s funding is set to run for another two years. ‘I don’t know if we’ll make a material that can be woven into a fabric,’ said Dhanak, ‘but we’re certainly moving in the right direction.’