A team of researchers at MIT have designed one of the lightest and strongest materials ever using graphene.
They made it by compressing and fusing flakes of graphene, a two-dimensional form of carbon.
The new material has just five per cent density and ten times the strength of steel, making it useful for applications where lightweight, strong materials are required.
The key factor that makes this new material strong is its geometrical 3-D form rather than the material itself, suggesting that other similar strong, lightweight materials could be made from a range of other substances by creating similar geometric structures.
The research, published in the journal Science Advances, has been attempted by other research groups, but experiments had failed to match predictions, with some results exhibiting less strength than expected.
The MIT team decided to analyze the material’s behavior down to the level of individual atoms within the structure.
Two-dimensional materials - flat sheets that are just one atom in thickness but can be indefinitely large in the other dimensions - are very strong and have electrical properties.
But because of their thinness, 'they are not very useful for making 3-D materials that could be used in vehicles, buildings, or devices,' said Dr Markus Buehler, head of MIT's department of Civil and Environmental Engineering (CEE) and one of the lead authors of the research.
'What we’ve done is to realize the wish of translating these 2-D materials into three-dimensional structures,' said Dr Buehler.
To make the material, the team compressed small flakes of graphene using heat and pressure.
This produced a strong, stable structure that resembles that of some corals and a tiny type of algae called a diatom.
'Once we created these 3-D structures, we wanted to see what’s the limit — what’s the strongest possible material we can produce,' said Zhao Qin, a CEE research assistant and one of the authors of the study.
To test how strong the material was, the researchers created a variety of 3-D models and then subjected them to various tests.
The new 3-D graphene material, which is composed of curved surfaces under deformation, reacts to force in a similar way to sheets of paper.
Paper doesn't have much strength along its length and width, and can be easily crumpled up.
But when its folded into certain shapes, for example rolled into a tube, the strength along the length of the tube is much greater and can support more weight.
In a similar way, the geometric arrangement of the graphene flakes naturally forms a very strong structure.
The material was made using a high-resolution, multimaterial 3-D printer.
Tests conducted by the MIT team ruled out a possibility proposed previously by other teams that it might be possible to make 3-D graphene structures lighter than air and used as a replacement for helium in balloons.
Instead, the material would not have enough strength and would collapse from the surrounding air pressure.
The researchers say that the material could have many applications in situations that require strength and light weight.
'You could either use the real graphene material or use the geometry we discovered with other materials, like polymers or metals,' Dr Buehler said, to gain similar advantages of strength combined with advantages in cost, processing methods, or other material properties (such as transparency or electrical conductivity).
'You can replace the material itself with anything,' Dr Buehler says.
'The geometry is the dominant factor. It’s something that has the potential to transfer to many things.'
The unusual geometric shapes that graphene naturally forms under heat and pressure look something like a Nerf ball — round, but full of holes.
These shapes, known as gyroids, are so complex that 'actually making them using conventional manufacturing methods is probably impossible,' Dr Buehler said.
The team used 3-D-printed models of the structure, enlarged to thousands of times their natural size for testing.
To actually make the material, the researchers suggest that one possibility would be to use the polymer or metal particles as templates, coat them with graphene by chemical vapor deposit before heat and pressure treatments, and then remove the polymer or metal phases to leave 3-D graphene in the gyroid form.
The same geometry could even be applied to large-scale structural materials.
For example, concrete for a structure such as a bridge might be made with this porous geometry, providing comparable strength with a fraction of the weight.
The material would also provide the added benefit of good insulation because of the huge amount of enclosed airspace within it.
Because the shape has very tiny pore spaces, the material might have applications in filtration systems for either water or chemical processing.
'This is an inspiring study on the mechanics of 3-D graphene assembly,” says Dr Huajian Gao, a professor of engineering at Brown University, who was not involved in this work.'
This work, Dr Gao says, 'shows a promising direction of bringing the strength of 2-D materials and the power of material architecture design together.'
Ultralight material could revolutionise gadget and even plane
A team of scientists has created a material that is thousands of times thinner than a sheet of paper, and is strong enough to maintain its shape even after being bent.
The tiny plates, made of aluminium oxide, are the first of their kind that can be manipulated by hand despite their nanoscale thinness.
A material of this strength and size could have applications in aviation, and even spur the development of insect-inspired flying robots.
Scientists have been working for years to design the thinnest, lightest material possible that is as strong as something of its size can be.
Now, researchers at the University of Pennsylvania have created just that.
'Materials on the nanoscale are often much stronger than you'd expect, but they can be hard to use on the macroscale,' says Igor Bargatin, Class of 1965 Term Assistant Professor of Mechanical Engineering and Applied Mechanics in Penn's School of Engineering and Applied Science, who led the study.
'We've essentially created a freestanding plate that has nanoscale thickness but is big enough to be handled by hand. That hasn't been done before.'
Normally, an object of such thinness will lose its original shape after being bent and twisted.
Graphene, a Nobel Prize winning material which can be as thin as a single carbon atom, must be stretched on a canvas in a frame in order to prevent curling.
This design, however, can return to its shape without any outside help.
'The problem is that frames are heavy, making it impossible to use the intrinsically low weight of these ultra-thin films,' Bargatin says.
'Our idea was to use corrugation instead of a frame.
'That means the structures we make are no longer completely planar, instead, they have a three-dimensional shape that looks like a honeycomb, but they are flat and contiguous and completely freestanding.'
'It's like an egg carton, but on the nanoscale,' added Prashant Purohit, an associate professor of mechanical engineering who also led the study.
The aluminium oxide plates are between 25 and 100 nanometers thick, and are stacked one atomic layer at a time.
Aluminium oxide, Bargatin explains, is actually a ceramic, which one would expect to crack easily. To the researchers' surprise, it did not crack.
'The plates bend, twist, deform, and recover their shape in such a way that you would think they are made out of plastic,' Bargatin says.
'The first time we saw it, I could hardly believe it.'
The honeycomb structure of the plates makes the material stiffer, preventing it from folding upon itself or getting stuck to something else. While a crack is possible, the structure prevents it from running all the way across.
'If a crack appears in our plates, however, it doesn't go all the way through the structure,' says Keivan Davami, a postdoctoral scholar who also led the study.
'It usually stops when it gets to one of the vertical walls of the corrugation.'
An insect wing is only a few microns thick, one researcher says, limited in size only by the thickness of cells.
This material, which weighs as little as a tenth of a gram per square meter, is up to ten times thinner than the thinnest man-made wing material.
New membranes deliver clean water more efficiently
Researchers from the Melbourne School of Engineering at the University of Melbourne, in conjunction with CSIRO, have developed new membranes or micro-filters that will result in clean water in a much more energy efficient manner.
Published recently in the journal Advanced Materials, the new membranes will supply clean water for use in desalination and water purification applications.
Sandra Kentish, Professor in the Department of Chemical and Biomolecular Engineering said that up until now, there has not been a way to add chlorinating agents to water to prevent biological growth in the desalination process.
"Such biofouling has been a major issue to date, but the new membranes have the potential to lead to a more economic desalination operation," she said.
For Professor Kentish, the availability of fresh water for drinking, irrigation and industrial use is one of the grand challenges of this century. Energy efficient water purification has the potential to improve the lives of billions of people around the world.
"The new membranes perform at a comparable level to existing commercial membranes used in these applications, but importantly show greater resistance to attack by chlorine containing chemicals," Professor Kentish said.
"The chlorine resistant membrane materials can cut out additional processing steps reducing operating costs. They can also prevent the decrease in water flow that is currently observed with time due to biological fouling" she said.
The novel membrane technology uses layer-by-layer polymer assembly and has been developed by a collaborative research team including Professor Kentish with Professor Frank Caruso and Dr Jacky Cho from the Melbourne School of Engineering and Dr Anita Hill from CSIRO. The work was made possible through funding from the Science and Industry Endowment Fund (SIEF).