Schematic diagram of a nanomaterial molecule.
Researchers at MIT have created a material that combines itself into nanoribbons by adding water. The material borrows from DuPont’s previously developed Kevlar composites for its orderly, tight structure, producing nanoribbons that are stronger than steel.
While most man-made materials are put together piece by piece by process and design, many products in nature are created by molecules that assemble themselves in an orderly fashion according to some unseen plan and without external forces. For example, self-assembly is almost ubiquitous in nature, from DNA material coiling and assembling itself into a sophisticated double helix structure, to large numbers of biomolecules arranging themselves to form the outer membrane of a cell.
Over the past two decades, scientists have taken note of this property and have been researching the creation of man-made objects with self-assembling properties. So far the main focus has been on designing molecular materials that can self-assemble in the presence of water for use in biochemistry, such as drug delivery or growing biomollusks. “These small molecule-based materials degrade quickly,” says Julia Ortony, assistant professor of materials and engineering at MIT, “and they are chemically unstable. Once they lose moisture, especially if they are then exposed to external forces, these structures disintegrate quickly.”
Now Ortony and colleagues invented this new material, not only self-assembly to form a very strong material, but also in the environment away from moisture to maintain their own structure.
The material has three layers; the outermost layer is hydrophilic, meaning these molecules prefer an environment with water; the middle layer is a tight structure like Kevlar that provides structural strength; and the inner material has hydrophobic properties, meaning they try to avoid being close to water. Such a structural distribution, Ottoni said, “provides the impetus for self-assembly, and these molecules automatically adjust their orientation to reduce the contact of the hydrophobic layer with water, forming a specific nanostructure.”
Ottoni describes the support provided by the tight structure of the middle layer, like Kevlar, so that the structure does not disintegrate as quickly as other similar materials in the event of loss of water. They found that the fabricated nanoribbon structure was stronger than they expected: surprisingly stronger than steel.
The group also wanted to see if the nanoribbons could be combined to create macroscopic materials, so they lined them up side by side and straightened them out to dry. It turned out that the wire-like material could support up to 200 times its own weight and had an aggressively small surface – only one metric gram per 200 square meters.
Research team member Ty Christoff-Tempesta said, “Such a high surface area to mass ratio allows this material to do more chemistry with a small amount.”
Using this property, researchers have developed nanoribbon materials with specific molecular coatings on the outside for pulling heavy metals such as lead or arsenic from contaminated water. Other applications include bundling the material into bundles for use inside electronic devices and batteries.
The study was published Jan. 21 in the journal Nature Nanotechnology.
Recent Comments