Defect annihilations in carbon nanotubes under thermo-mechanical loading

Topological defects can be formed in carbon nanotubes (CNTs) either during processing or during subsequent thermo-mechanical loading. When multiple defects are formed, the defects interact with each other depending upon the distance of separation between them. Earlier studies have shown that under mechanical loading, such interacting defects coalesce to form a larger defect, ultimately leading to complete failure. While defect coalescence is possible, it has also been observed that some defects may disappear (anneal) under certain thermo-mechanical conditions. In this molecular dynamics (MD) based simulation studies, we show that two 5-7-7-5 type defects (Stone-Wales) in close proximity when subjected to either pure mechanical loading (tensile strain of 10%) or pure thermal loading (temperature up to 3000 K) remain stable. On the other hand, the defects annihilate completely under a combination of both thermal (2800 K) and mechanical loading (under 5%) applied concurrently. It is hypothesized that vibrational oscillations due to thermal effects combined with atomic separation induced due to mechanical load together can cause the defects to annihilate while either of them acting alone cannot do so.