This image shows stress-induced deformation while pressure is applied and after it has been released. Image courtesy of the MIPT press office.
This image shows stress-induced deformation while pressure is applied and after it has been released. Image courtesy of the MIPT press office.

A Russian research team led by scientists at the Moscow Institute of Physics and Technology (MIPT) have managed to create an ultra-strong material by 'fusing' together multiwall carbon nanotubes (MWCNTs). Their findings are published in a paper in Applied Physics Letters.

According to the scientists, this novel MWCNT material is strong enough to endure very harsh conditions, making it useful for applications in the aerospace industry, among many others.

The research team performed a series of experiments to study the effect of high pressure on MWCNTs, which are cheaper to produce than their single-wall counterparts, and then used the results to simulate the behavior of nanotubes under high pressure. This revealed that the shear stress strain in the outer walls of the MWCNTs causes them to connect to each other as a result of structural rearrangements on their outer surfaces. The inner concentric nanotubes, however, retain their structure: they simply shrink under pressure and then return to their original shape once the pressure is released.

The scientists also demonstrated that covalent intertube bonding can give rise to interconnected (polymerized) multiwall nanotubes. "These connections between the nanotubes only affect the structure of the outer walls, whereas the inner layers remain intact. This allows us to retain the remarkable durability of the original nanotubes," says Mikhail Popov from the Department of Molecular and Chemical Physics at MIPT and head of the Laboratory of Functional Nanomaterials at the Technological Institute for Superhard and Novel Carbon Materials.

The scientists used a shear diamond anvil cell (SDAC) for the pressure treatment of the nanotubes, exposing them to pressures of up to 55GPa, which is 500 times the water pressure at the bottom of the Mariana Trench. The cell consists of two diamonds, between which samples of a material can be compressed. The SDAC is different from other cell types in that it can apply a controlled shear deformation to the material by rotating one of the anvils. The sample in an SDAC is thus subjected to pressure that has both a hydrostatic and a shear component, i.e. the stress is applied both normal and parallel to the sample’s surface.

Using computer simulations, the scientists found that these two types of stress affect the structure of the tubes in different ways. The hydrostatic pressure component alters the geometry of the nanotube walls in a complex manner, whereas the shear stress component induces the formation of amorphized regions on the outer walls, connecting them to the neighboring carbon tubes by means of covalent bonding. When the stress is removed, the shape of the inner layers of the connected multiwall tubes is restored.

Carbon nanotubes have a wide range of commercial applications by virtue of their unique mechanical, thermal and conduction properties. They are used in batteries and accumulators, tablet and smartphone touch screens, solar cells, antistatic coatings, and composite frames in electronics.

This story is adapted from material from the Moscow Institute of Physics and Technology, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.