Owrutsky (for Berman) - Molecular Dynamics and Theoretical Chemistry - Spring Review 2012

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Dr. Jeffrey Owrutsky presents an overview of Dr. Michael Berman's program - Molecular Dynamics and Theoretical Chemistry - at the AFOSR 2012 Spring Review.

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Owrutsky (for Berman) - Molecular Dynamics and Theoretical Chemistry - Spring Review 2012

  1. 1. MOLECULAR DYNAMICS & THEORETICAL CHEMISTRY 8 MAR 2012 Jeffrey C. Owrutsky / Acting for Michael Berman Program Manager AFOSR / RSA Integrity  Service  Excellence Air Force Research Laboratory15 February 2012 DISTRIBUTION A: Approved for public release; distribution is unlimited.
  2. 2. 2012 AFOSR SPRING REVIEWNAME: Jeff Owrutsky / Michael BermanBRIEF DESCRIPTION OF PORTFOLIO:Research on understanding and exploiting chemical reactivity and energy flowin molecules to improve Air Force systems, processes, and materials.Understanding and exploiting chemical reactivity and catalysis for improvedstorage and utilization of energyLIST SUB-AREAS IN PORTFOLIO:Molecular DynamicsTheoretical Chemistry Atmospheric & Space, Energetics, Nanostructures and Catalysis DISTRIBUTION A: Approved for public release; distribution is unlimited. 2
  3. 3. Challenges in Molecular Dynamics Molecular Dynamics, Theoretical Chemistry, Nanoenergetics• Energetic Materials (Rocket propellants, explosives) – Energetic ionic liquids  CHNO limit; new approaches – Energetic nanostructures  Sensitivity, mechanisms – Catalytic enhancement  Safer, penetrating munitions• Nanostructures/Sensors (Energy, catalysis, sensing) – Nanostructures for catalysis  Atomic scale imaging and control – Photoelectrochemical materials  Activity and stability – Plasmonics  Size- and shape-mediated properties• Atm/Space Chemistry (Signatures, surveillance) – Upper atmosphere, space  Hypersonic propulsion, gas/surf interact. – Signatures & backgrounds  Rates/mech. of ion-molecule reactions – Ion & plasma processes  Predictive codes, communication• Lasers and Diagnostics (Infrared lasers, missile defense) – High-Power Gas Lasers  Efficient pumping, energy transfer – Novel analytical tools/methods  Relaxation processes DISTRIBUTION A: Approved for public release; distribution is unlimited. 3
  4. 4. Scientific Challenges• Imaging and Control of Catalysis – Understanding control of mechanisms : – Comprehensive approach using emerging methods in • Synthesis - Prepare - Make • Simulation - Predict - Model • Sensing - Probe - Measure reactions: properties, interactions & mechanisms nanostructures to promote activity and stability – Catalysis is key to energy storage, fuel production and utilization – Important practical military and industrial impacts – Co-catalysts, promoters, substrates, new materials, …• Energetics – Enhance and improve energy density, impulse, stability DISTRIBUTION A: Approved for public release; distribution is unlimited. 4
  5. 5. Transformational OpportunitiesEndothermic Fuels forcooling high-speed vehicles Mission enabled by catalysis Secure Energy and Power – Alternatives fuels – Efficient generation vasst.info/ Propellants & Energetic Materials Hypergolic ionic liquids DISTRIBUTION A: Approved for public release; distribution is unlimited. 5
  6. 6. Related Work in Other Agencies• NSF – Solar Energy Initiative (SOLAR) – Center Powering the Planet – Chemistry Catalysis, Materials & Nanoscience Centers• DOE – Energy Frontier Research Centers, Solar Fuels Hub, JCAP – X-ray, electron, laser Facilities (Argonne, SLAC, ALS)• DOD – AFOSR fuel production complements ONR fuel utilization – Cooperation on energetic materials – AFOSR: physical chemistry oriented, molecular & mechanistic DISTRIBUTION A: Approved for public release; distribution is unlimited. 6
  7. 7. AFOSR Molecular Dynamics Program Strategy• Molecular / Chemical Physics Emphasis – Build from gas phase / small molecule – State selective energy, charge transfer & reactions – Connect to condensed phase – surfaces for catalysis – Model to practical system – Clusters & nanomaterials – unique behavior • post-ato-molecular and pre-bulk• Comprehensive & coordinated – Theory experiment – Systematic and probing • design rules - understanding for control • mechanisms for working systems / effects DISTRIBUTION A: Approved for public release; distribution is unlimited. 7
  8. 8. Program Trends • Catalysis – Networked, Actuated, Novel Probes • Sustainable Energy • Small Molecule Activation • Ionic Liquid Propellants • Plasmonics • Plasma / Ion Chemistry/ Interfaces • Hybrid Chemical Lasers • Sensors for Trace DetectionDISTRIBUTION A: Approved for public release; distribution is unlimited. 8
  9. 9. Transition: Mass Spectrometry and Ion Mobility Spectrometry Chemical Detection using Portable Instrumentation IntensityMiniaturized mass spectrometers (MSs) • real-time, in-field • atmosphere sampling • differential mobility spectrometry.Rapid Isotopic Distribution Analysis for Nuclear Forensics and Attribution using IMS/MS • High-resolution IMS separation of complex samples for isotopic distribution analysis. • To reduce sample analysis times from weeks (currently) to minutes/hours. DISTRIBUTION A: Approved for public release; distribution is unlimited. 9
  10. 10. Solar Fuels Two Tracks – Systematic and Following the Enigmatic• Two Tracks for CO2 reduction studies Catalysis – “Assembly Lines” for three step conversion of CO2 to methanol ‒ Systematic H2 + CO2 • understand geometric and energetic Formic acid catalyst HCOOH factors to promote reduction + H2 Formaldehyde catalyst • sequential reaction H2CO Methanol + H2 • identify barrier structures, reactions pathways catalyst CH3OH • determine mechanism of demonstrated system ‒ Understand Effective Systems Bocarsly organic reduction catalyst • Pyrdine on p-GaP • Homogeneous or heterogeneous mechanism? DISTRIBUTION A: Approved for public release; distribution is unlimited. 10
  11. 11. CO2 Reduction Motifs Ni cyclam – structurally Binding and Desorption Kinetics favorable for reduction Activity and Scaling Parameters• Extend to NiP2N2 • CO2 reduction - identify rate limiting• Mediated by hydride steps via DFT transfer energetics • CatApp – suncat.stanford.edu/catapp online surface specific barriers Kubiak, UCSD Norskov, Stanford DISTRIBUTION A: Approved for public release; distribution is unlimited. 11
  12. 12. Mechanism for CO2 Reduction?homogeneousmechanism: Morris, A. J.; McGibbon, R.T.; Bocarsly, A.B.heterogeneous ChemSusChem, 2011, 4, 191-196mechanism: = semiconductor/oxide surface DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution with pyridinyl radicals 12 DISTRIBUTION A: Approved for public release; distribution is unlimited. 12
  13. 13. Mechanism for CO2 Reduction?Energetics rules out CO2 reduction studies with related materialshomogeneous mechanism Reaction is surface-catalyzed  Reaction is robust and complicated • Imidazole catalyzes CO2 reductionHigh endoergicity due to electronic • MeOH with imidazole & histidine on gold structure of pyridinyl • Formic acid with imidazole on iron pyrite Carter, Princeton Bocarsly, Princeton DISTRIBUTION A: Approved for public release; distribution is unlimited. 13
  14. 14. Nanocatalysis for PropulsionMotivation : Endothermic Fuel for Hypersonic EngineThermal Control and More EfficiencyObjectives: Fundamentals relating to fuel-soluble/dispersiblecatalysts and precursorsChemistry • Active sites • Solubility • Active catalyst generation from precursors • Mechanisms • Energetics • Kinetics • Mixing • Droplets/vaporization/NP nucleation • Nanoscale fluid mechanicsPhysics DISTRIBUTION A: Approved for public release; distribution is unlimited. 14
  15. 15. Electronic Structure Controls Catalytic Activity• Nanocatalysts have activity that Pdn/TiO2(110) model catalyst Deviation from N-S Charge Scaling (eV) depends on particle size. 10 -0.4 Activity Activity (CO2 per TPR x109) Pd 3d XPS Shift• For the first time, activity was 8 correlated on an atom-by-atom Single Layer Islands -0.2 6 basis with particle electronic structure, and particle size. 4 Growth of 2nd Layer 0.0• Theorists from VCU and BNL are 2 calculating reasons for variation of 0.2 electronic properties with size 0 Clean 0 5 10 15 20 25 TiO2 Cluster Size (Number of Atoms)Oxygen activation efficiency: highly Pdn size dependent Comparison of CO oxidation activity with Pd 3d orbital energy (deviation from bulk-like scaling) Kaden, Wu, Kunkel, Anderson, Univ. of Utah - Science 326 (2009) 826-9 DISTRIBUTION A: Approved for public release; distribution is unlimited. 15
  16. 16. Dehydrogenation of Cyclohexene on Supported sub-nm Con Clusters Combined GISAXS/GIXAS/TPRx GISAXS: Evolution of a fluxional characterization nano-assembly from sub-nm Co clusters on MgO support• size–selected nanoparticle deposition • clusters are the most active on MgO support• in situ X-ray characterization under realistic • fluxional ~ 3 nm nanostructure – most reactive reaction conditions • cooling to RT reduces clusters size (?)• combined with catalyst tests Stefan Vajda et al , Argonne National Laboratory and Yale University DISTRIBUTION A: Approved for public release; distribution is unlimited. 16
  17. 17. Ultrafast Dynamics of SurfaceFunctionalized Heterogeneous Catalyst kecho = vibrational beam combiner k2+k3-k1 echo k1 k3 monochromator local oscillator k2 k3 k2 sample k1 MCT vibrational array echo 2D IR vibrational echo 1 t Tw 3 t spectroscopy on 2 t – coherence periods; Tw – population period surfaces . Surface – dry 150 ps (surface layer in air) Surface – wet 50 ps (surface layer in CHCl3) Solution 5 ps (head group in bulk CHCl3) Fayer (Stanford U.) and co-workers, Science 334, 634 (2011). DISTRIBUTION A: Approved for public release; distribution is unlimited. 17
  18. 18. Plasmon-enhanced PhotocatalyticActivity of Iron Oxide on Au Nanopillars • Enhanced (up to 50% over solar spectrum) photocurrent in a thin-film iron oxide photoanode coated on arrays of Au nanopillars. • Attributed primarily to the increased optical absorption from both surface plasmon resonances and photonic-mode light trapping in the nanosctructured topography. • The resonances can be tuned to a desirable wavelength by varying the thickness of the iron oxide layer. P. Yang (UC Berkeley) ACS Nano, 2011 DISTRIBUTION A: Approved for public release; distribution is unlimited. 18
  19. 19. Active optical nanoantennas A energy band diagram B• Hot electrons originating from the e- decay of surface plasmons, known laser B ITO Au EC Ti to mediate chemical reactions,can EF SiO 2 Sili con ) also be harvested in a device ype (n-t geometry C EV• Nanorod antennas - wavelength- Plasmonic metal antenna Si (n-type) dependent resonant response inject ITO contact indium contact hot electrons across metal- A 200 nm semiconductor interface: a 110 nm “nanoantenna-diode” 116 nm• Wavelength & polarization - specific Photocurrent spectra (a.u.) 122 nm photodetection 200 nm Absorption (a.u.) 128 nm 200 nm• Photodetection below the bandgap 134 nm of the semiconductor enables new 100 Current (% max) 140 nm 75 90 materials for infrared 146 nm 50 photosensitivity 25 152 nm 0 180 0 158 nm 25 50 75 270 1300 1450 1600 1300 1450 1600Halas (Rice) and coworkers Wavelength (nm) Wavelength (nm) 100Science 332, 702-4 (2011) A: Approved for public release; distribution is unlimited. DISTRIBUTION 19
  20. 20. Another Dimension: Networked or Actuated Catalysts • Expand capabilities expanded dimensions in structure or processes – modulated Field Mediated Nanoscale Dynamics catalysts • Time-, energy- and polarization- • Networked / building blocks – linking to resolved magneto-optical spectroscopy exploit coupling between units to study the optical properties of semiconducting nanostructure arrays. • Actuate/sequential – remediate to overcome poisoning for active catalysts • Magnetic field to control of the exciton fine structure populations of CdSe • Field or energized particle modification nanocrystals. • Plasma – catalyst hybrids BKnappenberger (FSU) and coworkers, J. Phys. Chem. C 115, 14517 (2011); FA9550-10-1-0300 DISTRIBUTION A: Approved for public release; distribution is unlimited. 20
  21. 21. Electric Field Control of a Metal Oxide-Catalyzed Reaction• Up to 63-fold change in product ratio induced by the voltage- controlled interfacial electric field• Field–dipole differentiation of transition states implicated Kanan (Stanford) and coworkers DISTRIBUTION A: Approved for public release; distribution is unlimited. 21
  22. 22. Directing the Motion of a Polymerization Motor Via Substrate Gradient• Polymerization motor for Janus nanoparticles collect at the gel edge over time in a gradient of norbornene• Control experiments with non-motor particles and non-polymerizable “fuel” showed no increase over time• Chemotaxis phenomenon – potential for system repair by directing the motor motion to a damaged spot Pavlick, Sengupta, Mcfadden, Zhang, Sen (Penn State) Chem. Int. Ed. 50, 9374 (2011) Angew. DISTRIBUTION A: Approved for public release; distribution is unlimited. 22
  23. 23. A Stable, Room Temperature IL Fuel Based on Borohydride Anion: [Al(BH4)4]- Ionic liquid propellents & energetic materials • trihexyl-tetradecyl-phosphonium (THTDP) cation - stable with bases and reducing agents* • THTDP reduces MP & promote liquidus • [Al(BH4)4]- also promotes liquidus [THTDP] [BH4] + Al (BH3) → *THTDP+ *Al (BH4) 4] Combined, the two ions create a low viscosity, hypergolic IL-fuel!FuelOxidizer 90%H2O2 98%H2O2 N2O4 WFNAR4P Al(BH4)4 Ignition Ignition Ignition ExplosiveIgnition Delay < 30ms < 30ms Vapor - ignition Stefan Schneider, Tom Hawkins, Yonis Ahmed, Michael Rosander, Jeff Mills and Leslie Hudgens , Angew. Chem. Int. Ed. 12 May 2011, DOI: 10.1002/anie.201101752 (AFRZ/RZ) DISTRIBUTION A: Approved for public release; distribution is unlimited. 23
  24. 24. Hypergolic Ionic Liquids and Metal Nanoparticles• Milling boron nanoparticles in ILs (Utah) Boron nanoparticles leads to air stable, unoxidized boron stabilized in [BMIM][DCA] nanoparticles - can be used for stable colloids in hypergolic ILs (Alabama).• Calculations (Edwards) suggest types of interactions between anions and a B80 cluster. Air Stable, unoxidized boron• IL remains hypergolic & boron adds from milling with ILs energetic value - longer ignition duration without increasing the ignition delay.• This leads to the ability to add a variety of metal, reactive nanoparticles into ionic liquids to tune their performance. A hypergolic IL, [BMIM][DCA] is still hypergolic even with boron nanoparticles incorporated. 1-butyl-3-methylimidazolium dicyanamide [BMIM][DCA] Rogers et al. DISTRIBUTION A: Approved for public release; distribution is unlimited. 24
  25. 25. Criticality and Vapor-Liquid Equilibrium of Ionic Liquids• Computed vapor-liquid phase equilibrium of a series of ionic liquids − Coexistence densities, vapor pressures, enthalpy and entropy of vaporization − Deduced the aggregation state of vapor phase• Provides key information for physical properties pertinent to energetics and fundamental experimentsMaginn (Notre Dame) and Rai; J. Phys. Chem. Lett. 2, 1439 (2011) DISTRIBUTION A: Approved for public release; distribution is unlimited. 25
  26. 26. Ionic Liquid Photoioniziation VUV Photoionization TOF Mass Spectroscopy • Aerosol, gentle production of IL ion pairs “cooler”, reduced internal energy • ALS soft ionization for low fragmentation • EMIM Br decomposes during evaporation • Hypergolic IL reaction products EMIM Br Leone (UC Berkeley) with Boatz, Vaghjiani & Chambreau (AFRL/RZ) DISTRIBUTION A: Approved for public release; distribution is unlimited.Distribution A: Approved for public release; distribution unlimited 26
  27. 27. Summary• Catalysis – transformational impacts on DoD systems – critical for efficient Power and Energy generation and utilization – propulsion / energetic material enhancements• Chemical dynamics – emerging methods and new insights into catalysis – intermediates and mechanisms needed to understand and optimize catalysts – AFOSR leading the way in applying new tools to understand catalytic mechanisms• Many new areas of opportunity: – alternative and renewable fuel production – atomic scale imaging and control of catalysis – new dimensions in catalyst and energetic material structures and control DISTRIBUTION A: Approved for public release; distribution is unlimited. 27

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