A new study discovered that when carbon nanotubes (CNTs) with hexagonal disclinations are twisted, they lose some of their mechanical strength.
This finding sheds light on the long-standing problem of CNT bundles and threads having low tensile strength, allowing them to be optimized for various uses.
(Photo: WikimediaCommons/division, CSIRO)
The Impact of Disclinations on CNT Strength
The Tokyo Institute of Technology team, led by Associate Professor Xiao-Wen Lei, published the work in the journal Carbon on May 30, 2024. Researchers used MD simulations and the Delaunay triangulation method to study CNT bundles (CNTBs) when twisted.
The study examined why CNTBs and yarn are weaker than CNTs when pulled apart, especially when twisted. Scientists are still determining why this performance drop is happening, which limits how these potential materials can be used in real life.
Lei said they had seen a drop in the CNTBs' Young's modulus because of the disclination lines. The Young's modulus was lower where the disclination lines were longer. He suggested that disclination lines in twisted CNTBs might be a major cause of the CNT yarns' weakening mechanical properties.
What are Carbon Nanotubes?
An essential type of nano-allotrope is carbon nanotubes. In 1991, Iijima found CNTs as rolled-up graphene sheets with sp2 bonds between the carbon atoms. Depending on how many rolled cylinders cover each other, they can have one, two, or more walls. The unique C-C bonding and cylinder shape of CNTs make them very strong, and this can be checked by putting them under pressure.
Much research has been done on the CNT nanostructure, diameter, length, and form. SWCNTs with chirality numbers n and m that are the same make up an armchair shape with a 0° angle. If m is zero, a 30-degree spiral is seen. The chirality of nanotubes is determined by these indices, which change their electrical, optical, mechanical, and other qualities.
MWCNTs comprise many cylinders of graphene that meet and are between 2 and 100 nm in size. On the other hand, SWCNTs are made up of a single rolled sheet of graphene about 1 nm in diameter. The length of carbon nanotubes varies by a few microns.
The Role of Disclinations
CNTBs have declined because of mistakes in the hexagonal layout of the CNTs. When these mistakes happen, a CNT is lost or added. MD simulations showed that twisting makes the disclination lines in CNTBs with extra layers long and bent.
Disclination lines change the mechanical properties of CNTB immediately. When these lines are bent, they lower Young's modulus, which makes the material less resistant to stretching. This study explains why twisted CNT yarns and bundles haven't reached their full strength yet.
Lei said that understanding the connection between changes in microscopic internal stacking structures and changes in mechanical qualities caused by lattice defects in materials could lead to a new field of study in computational materials science. He said very clearly that their main objective is for their research to help build an innovative, sustainable, and wealthy society shortly.
This work provides helpful information that might help improve high-performance CNT yarn. By working on disclinations, scientists want to make CNTs more useful in complex engineering applications.
The finding that disclinations weaken twisted carbon nanotubes is a big step forward in materials research. This new idea helps us learn more about CNTs and lets us use these materials best for future progress.
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