(543e) Elucidating Chemical Evolution in Shocked Materials

Understanding evolution of organic molecular materials (OMMs) subject to extreme temperature and pressure conditions (e.g., 1000s of K and 10s of GPa) is crucial to fields spanning astrobiology to nanomaterial fabrication. However, a confluence of challenges leaves a clear picture of this phenomena elusive. Experimentally, these conditions are often realized by subjecting samples to shockwaves via an external driver or detonation. Ensuing material evolution is rapid (e.g., occurring over 10^-9 – 10^-6s timescales) and often highly multiscaled (e.g., where reactivity, phase separation, and material strength are determined on approximately <10^-9 , 10^-7 , and 10^-6 m scales, respectively); as a result, direct experimental determination of properties as fundamental as temperature is intractable.

Atomistic simulations can be a powerful tool for shock experiment interpretation by providing an atomistically-resolved view into OMM evolution. However, characteristic problem scales approaching a μm and μs preclude use of highly predictive first principles-based simulation approaches (e.g., Kohn-Sham density functional theory), and existing molecular mechanics-based interatomic models are generally not designed for such high temperature and pressure conditions. Recently, the ChIMES machine-learned reactive interatomic model and development framework was developed to overcome these challenges. In this presentation, first-of-their-kind simulations using these models will be presented, and implications for our understanding OMMs evolution under extreme conditions are discussed.

This work is performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.