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

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.