Leeds researchers have discovered a new non-porous material that has unique and inherent ‘auxetic’ stretching properties.
A material that has an auxetic property means that when stretched, the material becomes thicker instead of thinner. So, instead of the material contracting in the middle as it is pulled at either end, it will expand.
LEMAS is a suite of advanced shared experimental facilities at Leeds - part of the new Bragg Centre
There are materials in nature that exhibit auxetic capabilities, such as cat skin, the protective layer in mussel shells and tendons in the human body.
Experts have been actively researching synthetic auxetic materials for more than 30 years, but until now, they have only been able to create them by structuring conventional materials using complex engineering processes, including 3D printing, yet these processes are time consuming, costly, and can lead to weaker, porous products.
Commercial applications
The identification of a synthetic molecular version is a major step forward for physicists, materials scientists and development companies, but researchers acknowledge that more work is needed to develop a better understanding of what drives the auxetic behaviour and how this behaviour can be applied commercially.
“Auxetics are great at absorbing energy and resisting fracture. There may be many potential applications for materials with these properties including body armour, architecture and medical equipment,” says Dr Devesh Mistry from the School of Physics and Astronomy, who led the research.
“This is a really exciting discovery, which will have significant benefits in the future for the development of products with a wide range of applications.”
This new synthetic material is inherently auxetic on the molecular level and is therefore much simpler to fabricate and avoids the problems usually found with engineered products, however more research is needed to understand exactly how they can be used.
“We have already submitted a patent and are talking to industry about the next steps,” adds Mistry.
Expanding the potential of liquid crystals
The team discovered the yet-to-be-named material while examining the capabilities of liquid crystal elastomers.
Liquid crystals are best known for their use in mobile phone and television screens and have both liquid and solid properties.
When they are linked with polymer chains to form rubbery networks, they have completely new properties and possible applications.
“Our results demonstrate a new use for liquid crystals beyond the flat screen monitors and televisions many of us are familiar with,” adds professor Helen Gleeson, study co-author and head of Physics and Astronomy at the university.
“This new synthetic material is a great example of what physics research and exploring the potential of materials such as liquid crystals can discover.”
Liquid crystal elastomer with auxetic capabilities
Image credit: Dr Devesh Mistry
Testing new materials
The instruments and expertise of staff in the Leeds Electron Microscopy and Spectroscopy Centre (LEMAS) at the university enabled the team to rigorously test the new material.
Gleeson says: “We wanted to be sure the material wouldn’t break down or become porous when stretched to its limits. Our LEMAS centre had the tools to do this.”
LEMAS is a suite of advanced shared experimental facilities at Leeds – also part of the new Bragg Centre of Materials Research – available for use by industry and other universities. Research into soft matter, such as liquid crystals, is one of six focus areas of the Bragg Centre.
The Centre brings together scientists and engineers to combine scientific discovery with applied science to support industry to develop advanced materials and so enable new devices, systems and applications.
“Collaboration between scientists with several areas of expertise and the extensive technical facilities we have at Leeds make this kind of exploration and discovery possible,” adds Gleeson.
The research has been published in the journal Nature Communications.
