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Vatamanu J.,University of Utah | Borodin O.,University of Utah | Borodin O.,Wasatch Molecular Inc. | Borodin O.,U.S. Army | Smith G.D.,University of Utah
Journal of Physical Chemistry B | Year: 2011

Molecular dynamics simulations were performed on N-methyl-N- propylpyrrolidinium bis(fluorosulfonyl)imide (pyr13FSI) room temperature ionic liquid (RTIL) confined between graphite electrodes as a function of applied potential at 393 and 453 K using an accurate force field developed in this work. The electric double layer (EDL) structure and differential capacitance (DC) of pyr13FSI was compared with the results of the previous study of a similar RTIL pyr 13bis(trifluoromethanesulfonyl)imide (pyr13TFSI) with a significantly larger anion [Vatamanu, J.; Borodin, O.; Smith, G. D.J. Am. Chem. Soc. 2010, 132, 14825 ]. Intriguingly, the smaller size of the FSI anion compared to TFSI did not result in a significant increase of the DC on the positive electrode. Instead, a 30% higher DC was observed on the negative electrode for pyr13FSI compared to pyr13TFSI. The larger DC observed on the negative electrode for pyr13FSI compared to pyr13TFSI was associated with two structural features of the EDL: (a) a closer approach of FSI compared to TFSI to the electrode surface and (b) a faster rate (vs potential decrease) of anion desorption from the electrode surface for FSI compared to TFSI. Additionally, the limiting behavior of DC at large applied potentials was investigated. Finally, we show that constant potential simulations indicate time scales of hundreds of picoseconds required for electrode charge/discharge and EDL formation. © 2011 American Chemical Society. Source

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. Source

Borodin O.,Wasatch Molecular Inc. | Borodin O.,University of Utah | Gorecki W.,Joseph Fourier University | Smith G.D.,University of Utah | Armand M.,University of Picardie Jules Verne
Journal of Physical Chemistry B | Year: 2010

The pulsed-field-gradient spin-echo NMR measurements have been performed on 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ([emim][FSI]) and 1-ethyl-3-methylimidazolium [bis[(trifluoromethyl)sulfonyl]imide] ([emim][TFSI]) over a wide temperature range from 233 to 400 K. Molecular dynamics (MD) simulations have been performed on [emim][FSI], [emim][TFSI], [N-methyl-N-propylpyrrolidinium][FSI] ([pyr13][FSI]), and [pyr 13][TFSI] utilizing a many-body polarizable force field. An excellent agreement between the ion self-diffusion coefficients from MD simulations and pfg-NMR experiments has been observed for [emim][FSI] and [emim][TFSI] ILs. The structure factor of [pyr13][FSI], [pyr14][TFSI], and [emim][TFSI] agreed well with the previously reported X-ray diffraction data performed by Umebayashi group. Ion packing in the liquid state is compared with packing in the corresponding ionic crystal. Faster transport found in the FSI-based ILs compared to that in TFSI-based ILs is associated with the smaller size of FSI- anion and lower cation-anion binding energies. A significant artificial increase of the barriers (by 3 kcal/mol) for the FSI - anion conformational transitions did not result in slowing down of ion transport, indicating that the ion dynamics is insensitive to the FSI - anion torsional energetic, while the same increase of the TFSI - anion barriers in [emim][TFSI] and [pyr13][TFSI] ILs resulted in slowing down of the cation and anion transport by 40-50%. Details of ion rotational and translational motion, coupling of the rotational and translational relaxation are also discussed. © 2010 American Chemical Society. Source

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.

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.

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