Laser-Induced Explosion of Nitrated Carbon Nanotubes: Nonadiabatic and Reactive Molecular Dynamics Simulations.

Abstract

Laser-initiated decomposition of carbon nanotubes (CNTs) can lead to medical, military, and other applications. In medicine, CNTs give rise to efficient remedies against diseases and malignant cells, since they encapsulate drug molecules, can be delivered inside living organisms, and absorb light that penetrates through biological tissues. As explosives, pyrotechnics, and propellants, CNTs can be activated remotely by a visible or infrared laser, avoiding the need for a detonating cord. The reported non-equilibrium investigation demonstrates the possibility of photoinduced polynitro-CNT explosion and provides a detailed chemical mechanism of the decomposition process, explicitly in the time domain. Nonadiabatic molecular dynamics (MD) performed with real-time time-dependent tight-binding density functional theory demonstrates that the photogenerated exciton deposits its energy into a broad range of phonon modes within less than a picosecond, resulting in a rapid polynitro-CNT heating. Following the heating, reactive MD demonstrates an explosion, during which the local temperature of polynitro-CNTs and its fragments rises as high as 4000 K. Photoexcitation of nitro groups by a high-energy laser is not required; the energy can be delivered to polynitro-CNTs using near-infrared light within the biological window. Furthermore, the explosion is possible both with and without an external oxygen source. Anaerobic explosion could be particularly beneficial in confined biological and nanoscale environments. The products of the polynitro-CNT decomposition are nontoxic: carbon dioxide and molecular nitrogen. The in silico demonstration of the laser-induced polynitro-CNT explosion, its chemical mechanism, and the time scales of physical and chemical transformations can be tested experimentally using time-resolved laser techniques.