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Molecular dynamics simulations of shock waves in oriented nitromethane single crystals.
Lan He1, Thomas D Sewell, Donald L Thompson
1Department of Chemistry, University of Missouri-Columbia, Columbia, Missouri 65211-7600, USA.
The Journal of Chemical Physics
|April 5, 2011
Summary
Shock waves in crystalline nitromethane show orientation-dependent structural relaxation. Different shock directions ([100], [010], [001]) cause unique responses, including plane-specific disordering and paracrystalline structures, impacting molecular mobility.
Area of Science:
- Materials Science
- Chemical Physics
- Computational Chemistry
Background:
- Understanding the behavior of energetic materials under shock compression is crucial for safety and performance.
- Crystalline nitromethane is a model energetic material whose response to shock is not fully understood.
- Previous studies have explored shock compression but lacked detailed molecular-level insights into structural relaxation.
Purpose of the Study:
- To investigate the structural relaxation of crystalline nitromethane under shock compression.
- To analyze the influence of shock wave orientation on the material's mechanical and thermal response.
- To elucidate the mechanisms of disordering and structural rearrangement at the molecular level.
Main Methods:
- Microcanonical molecular dynamics simulations were employed.
- The nonreactive Sorescu-Rice-Thompson force field was utilized.
- Simulations involved applying supported shocks (~15 GPa) along the (100), (010), and (001) crystal planes at 200 K.
Main Results:
- Shock response is highly dependent on shock wave orientation.
- Shocks along [100] and [001] induce plane-specific translational disordering.
- Shocks along [010] lead to a paracrystalline structure via complex rearrangement, with [001] showing more complete disordering.
- Transient intermolecular excitation is most pronounced for [010] shocks, followed by slower molecular vibrations.
- Net shock heating of 400-500 K was observed, with temperatures equilibrating by simulation end.
- Molecular translational mobility post-shock is highest for [001] and lowest for [010].
Conclusions:
- The orientation of shock waves significantly dictates the structural relaxation pathways in crystalline nitromethane.
- Plane-specific disordering and paracrystalline formation are key mechanisms for stress relief.
- Molecular dynamics simulations provide valuable insights into shock-induced phenomena in energetic materials.
- Results align with theoretical predictions regarding thermalization timescales.
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