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

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 Laboratory
15 February 2012 DISTRIBUTION A: Approved for public release; distribution is unlimited.

2. 2012 AFOSR SPRING REVIEW
NAME: Jeff Owrutsky / Michael Berman
BRIEF DESCRIPTION OF PORTFOLIO:
Research on understanding and exploiting chemical reactivity and energy flow
in molecules to improve Air Force systems, processes, and materials.
Understanding and exploiting chemical reactivity and catalysis for improved
storage and utilization of energy
LIST SUB-AREAS IN PORTFOLIO:
Molecular Dynamics
Theoretical Chemistry
Atmospheric & Space, Energetics, Nanostructures and Catalysis
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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
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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
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5. Transformational Opportunities
Endothermic Fuels for
cooling high-speed vehicles
Mission enabled by catalysis
Secure Energy and Power
– Alternatives fuels
– Efficient generation
vasst.info/
Propellants & Energetic Materials
Hypergolic ionic liquids
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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
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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
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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 Detection
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9. Transition: Mass Spectrometry and
Ion Mobility Spectrometry
Chemical Detection using Portable Instrumentation
Intensity
Miniaturized 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.
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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?
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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
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12. Mechanism for CO2 Reduction?
homogeneous
mechanism:
Morris, A. J.; McGibbon, R.T.; Bocarsly, A.B.
heterogeneous ChemSusChem, 2011, 4, 191-196
mechanism:
= semiconductor/oxide surface
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13. Mechanism for CO2 Reduction?
Energetics rules out CO2 reduction studies with related materials
homogeneous mechanism
 Reaction is surface-catalyzed  Reaction is robust and complicated
• Imidazole catalyzes CO2 reduction
High endoergicity due to electronic • MeOH with imidazole & histidine on gold
structure of pyridinyl • Formic acid with imidazole on iron pyrite
Carter, Princeton Bocarsly, Princeton
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14. Nanocatalysis for Propulsion
Motivation : Endothermic Fuel for Hypersonic Engine
Thermal Control and More Efficiency
Objectives: Fundamentals relating to fuel-soluble/dispersible
catalysts and precursors
Chemistry
• Active sites
• Solubility
• Active catalyst generation from precursors
• Mechanisms
• Energetics
• Kinetics
• Mixing
• Droplets/vaporization/NP nucleation
• Nanoscale fluid mechanics
Physics
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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
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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
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17. Ultrafast Dynamics of Surface
Functionalized 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).
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18. Plasmon-enhanced Photocatalytic
Activity 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
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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 1600
Halas (Rice) and coworkers Wavelength (nm) Wavelength (nm) 100
Science 332, 702-4 (2011) A: Approved for public release; distribution is unlimited.
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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
B
Knappenberger (FSU) and coworkers, J. Phys. Chem. C 115, 14517 (2011); FA9550-10-1-0300
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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
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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.
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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 WFNA
R4P Al(BH4)4 Ignition Ignition Ignition Explosive
Ignition 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)
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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.
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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 experiments
Maginn (Notre Dame) and Rai; J. Phys. Chem. Lett. 2, 1439 (2011)
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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)
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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
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