Search

Viscoelastic properties of the highly filled plastic-bonded explosive PBX-9501 were studied by two-dimensional dynamic material point method (MPM) simulations utilizing plasticized polymer binder and crystalline HMX constituent properties taken from experiment. The upper bound for the composite properties was estimated from iso-displacement boundary conditions, whereas the lower bound was estimated from iso-stress boundary conditions. A homogenized or 'dirty' binder approach was utilized to handle the multiple length scales involved in MPM simulations of highly filled composites with a broad distribution of filler particle sizes. Multiple time scale challenges were addressed by conducting a series of simulations in which the speed of sound of the composite was systematically varied by adjusting material point masses. This approach was used to predict the homogenized time dependent shear modulus of PBX-9501 from nanoseconds to milliseconds yielding good agreement with experimental data.

Interactions of Li + and BF − ions with TiO2 clusters were investigated using ab initio quantum chemistry methods. Classical force fields have been developed for poly(ethylene oxide)/LiBF4/TiO2, and molecular dynamics simulations have been performed on poly(ethylene oxide)/LiBF4 polymer electrolyte with and without embedded TiO2 nanoparticles using the developed force field. Addition of a TiO2 nanoparticle to PEO/LiBF4 solid polymer electrolyte resulted in the formation of a highly structured layer with a thickness of 5–6 A that had more than an order of magnitude slower mobility than that of bulk PEO/LiBF4. The PEO and ions in the layers extending from 6 to 15 A from the TiO2 nanoparticle also revealed some structuring and reduced dynamics, whereas the PEO/LiBF4 located further than 15 A was basically unaffected by the presence of the TiO2 nanoparticle. Both cations and anions tended to form a region with an increased concentration in the interfacial layers extending from 5 to 15 A. No ions were dissolved by the first interfacial layer of PEO. Addition of a nanoparticle with soft-repulsion interactions with PEO resulted in the formation of a PEO interfacial layer with reduced PEO density but increased ion concentration. The PEO and ion mobility in the interfacial layer next to the soft-repulsive nanoparticle were higher than those of bulk PEO/LiBF4 by 20–50%, whereas the conductivity of the nanocomposite electrolyte with the soft-repulsive particle increased only by 10%.

The structural properties of electrolytes consisting of solutions of ionic liquids in a polar solvent at charged electrode surfaces are investigated using classical atomistic simulations. The studied electrolytes consisted of tetraethylammonium tetrafluoroborate (NEt4-BF4), 1-ethyl-3-methylimidazolium tetrafluoroborate (c2mim-BF4) and 1-octyl-3-methylimidazolium tetrafluoroborate (c8mim-BF4) salts dissolved in acetonitrile solvent. We discuss the influence of electrolyte concentration, chemical structure of the ionic salt, temperature, conducting versus semiconducting nature of the electrode, electrode geometry and surface roughness on the electric double layer structure and capacitance and compare these properties with those obtained for pure room temperature ionic liquids. We show that electrolytes consisting of solutions of ions can behave quite differently from pure ionic liquid electrolytes.

We describe the development of a large-scale high-throughput application for discovery in materials science. Our point of departure is a computational framework for distributed multi-scale computation. We augment the original framework with a specialized module whose role is to route evaluation requests needed by the high-throughput application to a collection of available computational resources. We evaluate the feasibility and performance of the resulting high-throughput computational framework by carrying out a high-throughput study of battery solvents. Our results indicate that distributed multi-scale computing, by virtue of its adaptive nature, is particularly well-suited for building high-throughput applications.