(52f) Dissipative Particle Dynamics Simulations Involving Chemical Reactions

Many applications of solid composite materials involve chemical energy release.  For example, energetic materials, composites of high-energy, high-density crystallites and polymer binder, are used as explosives, propellants and detonators.  Likewise, microstructured metallic systems are of interest in many different areas, including soldering in electronic-parts assembly and thermites for biocidal applications [1].  Energy exchange mechanisms for these materials occur over many length and time scales, where the energy release rate is intimately controlled by the nano- and microstructure of the composite, such as the crystallite size distribution, porosity, defects, and passivation layer.

For such systems, modeling and simulation is a useful tool, since it is not hampered by the experimental challenges caused by the steep thermal and chemical gradients.  Rather, limitations are due to the approximations made in the models, computational resources, and the available methodologies.  For example, continuum scale modeling can depict macro-scale events; however, it lacks the modeling fidelity to properly include material microstructure that influences the overall behavior.  While atomistic-level simulations can provide more detailed descriptions, these simulations cannot access the length and times scales necessary to adequately model a microstructurally-heterogeneous material.  These well-recognized limitations at either scale have motivated us to develop particle-based simulation models and methods to bridge these spatial and temporal modeling regimes while ensuring multiscale consistency.  The approach must be capable of capturing the known thermo-mechanical responses for these systems, including phase transitions, structural rearrangements, and chemical reactions.

In this talk, we will present the status of this ongoing project.  To date, progress has been encouraging, where we find the constant-energy and constant-enthalpy Dissipative Particle Dynamics (DPD) methods [2-4] coupled with accurate coarse-grain models [5, 6] to be viable tools for simulating condensed-phase reactive events.  The focus of this talk is on our recent work in developing a method within the DPD framework that can capture chemical reactivity.  The approach, inspired by the work of Maillet and co-workers [7], treats the coarse-grain particle as a microreactor as opposed to a methodology that requires a reactive-type interaction potential.  An additional progress variable is assigned to each particle that monitors the “extent-of-reaction” associated with reactions occurring within each particle.  Particles are allowed to shrink and swell to account for volume changes associated with reactivity.  Current applications are for simple, model reacting systems, however, extensions to complex reacting systems are underway, where both top-down and bottom-up parameterization is being utilized.

This effort is supported by the Institute for Multi Scale Reactive Modeling of Insensitive Munitions (MSRM), which is a multi-team effort led by the U.S. Army Research Laboratory and the U.S. Army Armament Research, Development and Engineering Center, involving various other national laboratories and academic groups totaling over 20 scientists.  ML acknowledges funding through a Cooperative Agreement with the U.S. Army Research Laboratory.

References

1.  National Academy of Sciences Report, Advanced Energetic Materials, National Research Council, National Academy Press (2004).

2.  J. Bonet Avalos and A.D. Mackie, Europhysics Letters, 40, 141 (1997).

3.  P. Español, Europhysics Letters, 40, 631 (1997).

4.  M. Lísal, J.K. Brennan and J. Bonet Avalos, J. Chem. Phys., submitted (2011).

5.  S. Izvekov, P.W. Chung, and B.M. Rice, J. Chem. Phys., 133, 064109 (2010).

6.  S. Izvekov, P.W. Chung, and B.M. Rice, J. Chem. Phys., submitted (2011).

7.  J.B. Maillet, L. Soulard and G. Stoltz, Europhys. Lett., 78, 68001 (2007).