Molecular Dynamics Simulations of Shock Wave Propagation through the Crystal-Melt Interface of (100)-Oriented Nitromethane

S Jiang and TD Sewell and DL Thompson, JOURNAL OF PHYSICAL CHEMISTRY C, 120, 22989-23000 (2016).

DOI: 10.1021/acs.jpcc.6b07002

Molecular dynamics (MD) simulations were used to study shock wave passage with normal incidence through the equilibrium interface between (100) oriented nitromethane and the melt. The simulations were performed,using the fully flexible, nonreactive SRT force field (Sorescu, D. C.; Rice, B. M.; Thompson, D. L. The Journal of Physical Chemistry B 2000, 104, 8406-8419). The local kinetic energies (intermolecular, intramolecular, and total) and stress states differ significantly in the liquid and crystal regions; and depend on whether the shock is initiated in the crystal or liquid. The number and spatial distributions of shock-induced molecular disorientations in the crystal for shocks initiated in the crystal are Similar to those obtained for analogous simulations for a completely crystalline sample; however, substantial differences in the extent and distribution of shock-induced molecular disorientations in the crystal region were observed when the shock initiated in the liquid. All three measures of kinetic temperature in the crystal region are higher. hen the shock is initiated in the crystal than when it is initiated in the liquid. Kinetic temperature profiles exhibit features in the vicinity of the interface Considerably different from those in either bulk phase The shock-induced local mechanical states (von Mises stress) indicate that the crystal is less able to support shear stresses when the shock is initiated in the crystal than when it is initiated in the liquid. There is a strong reflection back into the liquid when the shock wave passes through the liquid and encounters the interface with the crystal. This causes a large increase in the potential energy of the liquid and limits the amount of energy transmitted into the crystal, which limits the molecular disorientations in the crystal. Thus, a shock from liquid to crystal yields less inelastic deformation in the crystal.

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