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Li Z.,University of Utah | Smith G.D.,Wasatch Molecular Inc. | Bedrov D.,University of Utah
Journal of Physical Chemistry B | Year: 2012

Molecular dynamics simulations of N-methyl-N-propylpyrrolidinium (pyr 13) bis(trifluoromethanesulfonyl)imide (Ntf2) ionic liquid [pyr13][Ntf2] mixed with [Li][Ntf2] salt have been conducted using a polarizable force field. Mixture simulations with lithium salt mole fractions between 0% and 33% at 363 and 423 K yield densities, ion self-diffusion coefficients, and ionic conductivities in very good agreement with available experimental data. In all investigated electrolytes, each Li + cation was found to be coordinated, on average, by 4.1 oxygen atoms from surrounding anions. At lower concentrations (x ≤ 0.20), the Li + cation was found to be, on average, coordinated by slightly more than three Ntf2 anions with two anions contributing a single oxygen atom and one anion contributing two oxygen atoms to Li+ coordination. At the highest [Li][Ntf2] concentration, however, there were, on average, 3.5 anions coordinating each Li+ cation, corresponding to fewer bidendate and more monodentate anions in the Li+ coordination sphere. This trend is due to increased sharing of anions by Li+ at higher salt concentrations. In the [pyr13][Ntf2]/[Li] [Ntf2] electrolytes, the ion diffusivity is significantly smaller than that in organic liquid electrolytes due to not only the greater viscosity of the solvent but also the formation of clusters resulting from sharing of anions by Li+ cations. The ionic conductivity of the electrolytes was found to decrease with increasing salt concentration, with the effect being greater at the higher temperature. Finally, we found that the contribution of Li+ to ionic conductivity does not increase proportionally to Li + concentration but saturates at higher doping levels. © 2012 American Chemical Society.


Xing L.,University of Utah | Xing L.,South China Normal University | Vatamanu J.,University of Utah | Smith G.D.,Wasatch Molecular Inc. | Bedrov D.,University of Utah
Journal of Physical Chemistry Letters | Year: 2012

Electrostatic double-layer capacitors (EDLCs) with room-temperature ionic liquids (RTILs) as electrolytes are among the most promising energy storage technologies. Utilizing atomistic molecular dynamics simulations, we demonstrate that the capacitance and energy density stored within the electric double layers (EDLs) formed at the electrode-RTIL electrolyte interface can be significantly improved by tuning the nanopatterning of the electrode surface. Significantly increased values and complex dependence of differential capacitance on applied potential were observed for surface patterns having dimensions similar to the ions' dimensions. Electrode surfaces patterned with rough edges promote ion separation in the EDL at lower potentials and therefore result in increased capacitance. The observed trends, which are not accounted for by the current basic EDL theories, provide a potentially new route for optimizing electrode structure for specific electrolytes. © 2012 American Chemical Society.


Hooper J.B.,Wasatch Molecular Inc. | Borodin O.,Wasatch Molecular Inc.
Physical Chemistry Chemical Physics | Year: 2010

A quantum chemistry based, dipole polarizable force field has been used to simulate the N,N,N,N-tetramethylammonium (TMA) dicyanamide (DCA) ionic salt, in both plastic crystalline and liquid phases. Simulations predicted the [TMA][DCA] crystal structure and dimensions in good agreement with experiment. Ion-counterion spatial distributions are used to understand the local environment and ion pairing of both ions in crystalline and liquid phases. The rotational dynamics of ions in the crystalline system are thoroughly explored. Arrest of the DCA rotational degrees of freedom was associated with the experimentally observed solid-solid phase transitions. The self-diffusion coefficient and conductivity were calculated for the liquid state; however no net ion diffusion is noted in the pristine crystalline state. Introduction of ion vacancy at 0.3% concentration is found to be sufficient to enable ion diffusive behavior and conduction at 425 K in the crystalline state, with good agreement found between the experimental and simulated conductivity. © the Owner Societies.


Bedrov D.,Wasatch Molecular Inc. | Borodin O.,Wasatch Molecular Inc.
Journal of Physical Chemistry B | Year: 2010

Molecular dynamics simulations of ionic liquids (IL) comprised of 1-butyl-3-methylimidazolium [bmim] cation and nitrate [NO3], azide [N3], or dicyanamide [N(CN)2] anions were conducted using the polarizable APPLE&P force field. Comparison of thermodynamic properties such as densities, enthalpies of vaporization, and ion binding energies as well as structural correlations obtained from simulations at atmospheric pressure and temperature range 298 - 393 K showed that IL with the N(CN)2 anion shows significantly different characteristics as compared to ILs with the N 3 and NO3 anions. [bmim][N(CN)2] IL was found to have the lowest enthalpy of vaporization and the weakest ion - ion structural correlation as compared to ILs with the other two ions. This trend was further manifested in dynamical properties characterized by self-diffusion coefficients and molecular rotational relaxation times, where IL with the N(CN)2 anion showed the fastest dynamics as compared to other ILs. We also examine the dynamic correlations between the ions' translational and rotational motions as well as discuss the anisotropy of the latter. © 2010 American Chemical Society.


Grant
Agency: Department of Defense | Branch: Air Force | Program: STTR | Phase: Phase I | Award Amount: 150.00K | Year: 2015

ABSTRACT: We will develop a multiscale molecular dynamics/material point method (MD/MPM) methodology for determining the response of PBXs to a wide range of loading conditions as a function of mesoscale structure with emphasis on accurate representation of interfacial physics. The initial material of choice will be HMX + DOA plasticized HTPB binder. Velocity-dependent grain-grain and viscoelastic grain-binder interfacial models as well as an improved viscoelastic model for the binder will be developed based upon non-equilibrium and Hugoniostat MD simulations. An array of representative mesoscale multiple grain elements (MGEs) will be generated using a Monte Carlo packing and growth (MCPG) methodology employing ellipsoidal particles for a range of configurations/formulations (grain size distributions/loading fractions). MGE generation will be biased to yield controlled degrees of grain-grain contact based upon previous experimental mesoscale structural analyses. MPM computational experiments (quasistatic loading and shock) performed on multiple MGEs with fully resolved grains, binder and interfaces will yield mesoscale structure-dependent properties (EOS and constitutive laws). These mesoscale structure-dependent properties will be employed in MPM simulations of bulk PBXs over a wide range of loading conditions and particle resolution with explicit mesoscale heterogeneity implemented through stochastic property seeding. Extensive hot spot analyses will be conducted and correlated with mesoscale structure.; BENEFIT: The objectives of this STTR project are of interest to the DOD, other government agency and industrial concerns interested in production of PBXs with controlled sensitivity as well as those interested in improving the safety of solid propellants. In addition to software licensing to interested users, success of this Phase I project will allow WMI to pursue patents and subsequent licensing and royalties for all developed materials where this is allowable.


Grant
Agency: Department of Defense | Branch: Navy | Program: SBIR | Phase: Phase I | Award Amount: 80.00K | Year: 2013

A multiscale modeling approach is proposed for the development and implementation of physics-based EOS and constitutive models within a multimaterials continuum modeling framework. Accurate EOS and rate-dependent constitutive (flow, yield stress, damage) models for plate glass, PMMA and segmented elastomers will be developed based upon equilibrium and non-equilibrium molecular dynamics simulations and will be validated through direct comparison of predicted impact behavior with experimental measurements. MD simulations will also facilitate development of improved interfacial models needed for prediction of wave propagation in multilayered materials. The material point method (MPM) will implement these models as well as improved 2- and 3-D crack propagation, fracture, failure and materials interface models, allowing for accurate numerical assessment and optimization of layered structures of various materials and geometries to resist ballistic and blast impact.


Grant
Agency: NSF | Branch: Standard Grant | Program: | Phase: | Award Amount: 150.00K | Year: 2013

This Small Business Innovation Research (SBIR) Phase I will focus on development of novel biopolymers obtained by covalently attaching peptide side chains to hyaluronic acid (HA) backbone polymer chains through carefully controlled chemistry. The resulting material can be used for soft tissue augmentation, protection, and rejuvenation. The work will rely on a combined experimental and molecular modeling approach. In this novel approach, the synthesized polypeptide-HA polymer is an in-situ gelling biomaterial that self-assembles into a physical gel inside the body driven by hydrophobic attractions between the peptide side chains. Molecular modeling will guide the synthesis of polypeptide-HA polymers that form gels with desired mechanical and osmotic properties. The physical crosslinks in the gel can be reversibly broken down by high shear forces in the injection needle, allowing use of a narrow gauge injection needle that reduces patient pain and allows for formation of stiffer, more resilient gels. The innovative biopolymer is likely to outperform currently used biomaterials because of in-situ gelling, better control of and accessibility to a wider range of gel properties and the side chains can be used to carry molecules with biological functionality.

The broader impact/commercial potential of this project will be a new material that can meet requirements for an ideal HA-containing dermal filler. These requirements include a material that is pain-free and easy-to-inject into the body, in vivo survivability for at least one year, absence of immunogenic or allergic reactions, enhanced water retention, tunable mechanical properties, attachment of functional molecules, and low cost. Such a material will significantly enhance capabilities for soft tissue augmentation over existing HA-based materials and will be in large demand. The properties of the novel biopolymer can be tuned for other important and growing biomedical applications such as viscosupplementation for arthritic joints and ocular antioxidant protection. The proposed combined experimental and molecular modeling approach will also provide a unique fundamental understanding of the interplay between molecular characteristics (composition and architecture) and macroscopic properties (mechanical and transport properties) of gels and solutions comprised of these molecules. The proposed molecular simulation guided material design approach is a state-of-the-art technology that can be extended for development of other complex materials.


Grant
Agency: Department of Defense | Branch: Air Force | Program: SBIR | Phase: Phase II | Award Amount: 746.71K | Year: 2010

The objective of this work is to provide guidance to explosive formulators and facilitate the development of improved penetrator explosives. Because of the complexity of these materials, it is difficult to relate parameters controllable during formulation to desirable properties in the final product. Formulation variations are limited to modifying the individual constituents in a formulation, their ratios, and the processing methods used, such as mixing and casting techniques. Most commonly, varying a single formulation parameter results in the variation of multiple mesoscale characteristics. It is well established that the mesoscale characteristics of energetic materials are responsible for energy localization and generating damage, “hot spots” and/or bulk reaction. The major impediment to understanding the influence of formulation parameters on explosive sensitivity is that formulation parameters are rarely synonymous with mesoscale characteristics. This is an ideal scenario for contributions via numerical simulation, where the mesoscale characteristics can be individually varied. Isolating the effects of a mesoscale characteristic allows its individual effect on sensitivity to be determined, as well as its relative importance to other mesoscale characteristics, allowing the relevant, irrelevant, and competing consequences of a formulation modification to be identified and evaluated. Similarly, the paramount considerations in developing a new formulation may be identified. BENEFIT: Various formulation variations and their mesoscale effects will be investigated and ranked in order of their importance in penetrator explosive sensitivity. The modeling of energetic constituents and their interactions will be improved and validated. Numerical experiments will be designed to elucidate statistically significant mesoscale effects on bulk response, hot spot distributions, and sensitivity. A suite of experimental results will be generated to characterize bulk and mesoscale response of these materials and validate simulations. WMI will use a two-pronged approach to address the needs of customers who desire to utilize mesoscale simulations to guide the formulation of energetic materials. The first approach is to perform proprietary research and development services. Such R&D services are especially attractive to customers with no current in-house simulation capabilities, yet wishing to fully benefit from the utility and power of mesoscale modeling. The second approach is to release for sale parameterizations of the material and interfacial models developed. This effort targets customers with simulation experience and tools, but who are in need of more sophisticated modeling approaches.


Grant
Agency: National Science Foundation | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 150.00K | Year: 2013

This Small Business Innovation Research (SBIR) Phase I will focus on development of novel biopolymers obtained by covalently attaching peptide side chains to hyaluronic acid (HA) backbone polymer chains through carefully controlled chemistry. The resulting material can be used for soft tissue augmentation, protection, and rejuvenation. The work will rely on a combined experimental and molecular modeling approach. In this novel approach, the synthesized polypeptide-HA polymer is an in-situ gelling biomaterial that self-assembles into a physical gel inside the body driven by hydrophobic attractions between the peptide side chains. Molecular modeling will guide the synthesis of polypeptide-HA polymers that form gels with desired mechanical and osmotic properties. The physical crosslinks in the gel can be reversibly broken down by high shear forces in the injection needle, allowing use of a narrow gauge injection needle that reduces patient pain and allows for formation of stiffer, more resilient gels. The innovative biopolymer is likely to outperform currently used biomaterials because of in-situ gelling, better control of and accessibility to a wider range of gel properties and the side chains can be used to carry molecules with biological functionality. The broader impact/commercial potential of this project will be a new material that can meet requirements for an ideal HA-containing dermal filler. These requirements include a material that is pain-free and easy-to-inject into the body, in vivo survivability for at least one year, absence of immunogenic or allergic reactions, enhanced water retention, tunable mechanical properties, attachment of functional molecules, and low cost. Such a material will significantly enhance capabilities for soft tissue augmentation over existing HA-based materials and will be in large demand. The properties of the novel biopolymer can be tuned for other important and growing biomedical applications such as viscosupplementation for arthritic joints and ocular antioxidant protection. The proposed combined experimental and molecular modeling approach will also provide a unique fundamental understanding of the interplay between molecular characteristics (composition and architecture) and macroscopic properties (mechanical and transport properties) of gels and solutions comprised of these molecules. The proposed molecular simulation guided material design approach is a state-of-the-art technology that can be extended for development of other complex materials.


Grant
Agency: Department of Defense | Branch: Air Force | Program: SBIR | Phase: Phase II | Award Amount: 749.93K | Year: 2011

ABSTRACT: Building on the demonstrated in Phase-I success of application of molecular dynamics (MD) simulations for investigation of hypergolic and non-hypergolic ionic liquid(IL)-based fuels, we propose to develop and validate a set of simulation tools and empirical correlations that will allow to predict hypergolicity of a wide variety IL/oxidizer combinations. The proposed simulation tools will include MD simulations that utilize fully atomistic reactive (ReaxFF) and polarizable non-reactive (APPLE & P) force fields. Utilization of both reactive and non-reactive force fields will allow efficient and accurate modeling of chemical reactions and thermophysical properties that can be subsequently used for establishing quantitative structure-property relationships (QSPR) with hypergolicity as well as direct modeling of hypergolic behavior. BENEFIT: Tools developed in this proposal will enhance and shorten the design cycle for the development of novel, IL-based hypergolic fuels. These tools will be also applicable for a variety of technological applications where reactions of IL play an important role. Examples of such technologies include pharmaceutical processes, biomass production, and energy storage (batteries and super capacitors).

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