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  • Structure and Modelingof Polyhedral Oligomeric Silsesquioxane

    (POSS) Systemsby

    Stanley Anderson (Westmont College) Michael Bowers (UCSB)

    Erin Shammel Baker , Jennifer Gidden (UCSB) Shawn Phillips, Tim Haddad, Sandra Tomscak,

    (Edwards Air Force Base)

  • AcknowledgmentsProf. Michael T. Bowers

    Bowers Group:Erin Shammel Baker Dr. Thomas WyttenbachDr. Jennifer GiddenDr. John Bushnell

    Edwards AFB POSS GroupShawn Phillips,Tim Haddad,Sandra Tomczyk, Joe Mabry

    $$$$AFOSR

    NRC/NAS Senior Associateship

  • Outline

    Introduction and Concepts

    Ion Mobility Experiment

    Modeling Structures with AMBER

    Some Examples of POSS Studies

  • Drift cell

    E

    p(He)

    IonFelFfriction

    v = const.v = K EK = ion mobility

    Concepts

  • K = f (T, p, q, , )

    T = temperaturep = pressureq = ion charge = reduced massK = ion mobility = collision cross section

    = f ( )Heion interactionIon shape

  • Ion Mobility Experiment

    in out

    Drift cell

    E

    15 torr He

    IonSource

    IonSource MS2MS2 DetectorDetectorMS1MS1

    DriftCell

    DriftCell

    vd

  • Ion Mobility Experiment

    in out

    Drift cell

    IonSource

    IonSource MS2MS2 DetectorDetectorMS1MS1

    DriftCell

    DriftCell

    vd

  • Source

    TOFDrift Cell

    Quadrupole

    TOF DetectorGlassl = 20 cmp = ~1.5 torr He

    h

    Erin S. Baker, Jennifer Gidden, David P. Fee, Paul R. Kemper, Stanley E. Anderson, and Michael T. Bowers, Int. J. Mass Spectrom. 2003, 227, 205-216.

    Time-of-Flight (TOF) Mass SpectrometryTOF Mode

  • TOFDrift Cell

    TOF Detector

    h

    Quadrupole

    Time-of-Flight (TOF) Mass SpectrometryTOF Mode

    m/z

    Mass SpectrumSource

  • TOFDrift Cell

    Detector

    h

    Source

    Quadrupole

    Time-of-Flight (TOF) Mass SpectrometryIon Mobility Mode

    Glass, l = 20 cmp = ~1.5 torr HeE = 100 - 300 v

    Single Structure

    Multiple Structures

    Arrival Time Distributions

    Source

    + -

  • Experiment versus Theory

    Experimental Method

    ATD Mobility (K)

    Time (s)

    Inte

    nsi

    ty oAd tt

    lEKv

    ==

  • Experiment versus Theory

    Experimental Method

    ATD Reduced Mobility (Ko)

    Time (s)

    Inte

    nsi

    ty oAd tt

    lEKv

    ==

    273760 T

    pKK o=

    lVE =

  • Experiment versus Theory

    Experimental Method

    ATD Reduced Mobility (Ko)

    Time (s)

    Inte

    nsi

    ty oAd tt

    lEKv

    ==

    273760 T

    pKK o=

    lVE =

    oo

    A tVp

    TKlt +

    =

    27376012

  • Experiment versus Theory

    Experimental Method

    p/V (torr/V)

    0.0 0.005 0.01

    t A(

    s)

    1000

    500

    1500

    2000

    2500

    Reduced Mobility (Ko)

    oo

    A tVp

    TKlt +

    =

    27376012

    TKlslope

    o

    27376012

    =

  • Experiment versus Theory

    Experimental Method

    Collision Cross-Section ()Reduced Mobility (Ko)

    obo KTkNe 12

    163

    2/1

    =

    TslopelKo

    27376012

    =

    )1,1(

  • AMBER(Annealing/Energy Minimization)

    Experiment versus Theory

    Theoretical Method

    Molecular Mechanics/Dynamics Structures

  • AMBER(Annealing/Energy Minimization)

    Dynamics simulations for 30 ps at 600-1400K

    Cool structures to 50K using 10 ps dynamics

    Energy minimize the structure

    Use final structure as initial structure for next cycle

    Experiment versus Theory

    Theoretical Method

    Molecular Mechanics/Dynamics Structures

  • Experiment versus Theory

    Theoretical Method

    Structures Collision Cross-Sections ()

    Relative Energy (kcal/mol)

    -5 0 10 15 20 25220

    240

    260

    280

    Cro

    ss-S

    ecti

    on

    (

    2 )

    SIGMA

    5

  • Experiment versus Theory

    Molecular Mechanics/Dynamics Structures Collision Cross-Sections ()

    ATDs Mobilities (K) Collision Cross-Sections ()

    Compare

    Experimental Method:

    Theoretical Method:

  • Examples of Bowers Group Research Projects

    Silicon-Oxygen Cage (POSS) Monomer and Polymer Characterization

    Polyvinylene Polymers

    Structure of Silver Clusters Deposited on Surfaces

    Structure of DNA Double-Helix Oligomers

    Structure of Oxytocin and the Role of Metal Ions

    Beta-Amyloid (Alzeimers) Protein Structures

  • Examples of Bowers Group Research Projects

    Silicon-Oxygen Cage (POSS) Monomer and Polymer Characterization

    Polyvinylene Polymers

    Structure of Silver Clusters Deposited on Surfaces

    Structure of DNA Double-Helix Oligomers

    Structure of Oxytocin and the Role of Metal Ions

    Beta-Amyloid (Alzeimers) Protein Structures

  • Why Study Silicon-Based Materials?

    A wide range of application from polymer modifiers to lubricants

    Improves physical and thermal properties of polymer systems

    Addition of silicon-oxygen substituentsgives polymers with extended temperature ranges reduced flammability lower thermal conductivity reduced viscosity resistance to atomic oxygen low density

    Major interest and funding by the Air Force!

  • Si

    Si

    O

    O

    Si

    Si

    Si

    Si

    O

    O

    O

    O

    SiO

    Si

    O

    OO

    OO

    R R

    R

    R

    R

    R

    R X

    Anatomy of a Polyhedral OligomericSilsesquioxane (POSS) Molecule

    May possess one or more reactive groups suitable forpolymerization or grafting.

    Thermally and chemically robust hybrid (organic-inorganic) framework.

    Nanoscopic in size with an Si-Sidistance of 0.5 nmand a R-R distance of 1.5 nm.

    Nonreactive organic (R) groups for solubilization and compatibilization.

    Precise three-dimensional structure for molecular levelreinforcement of polymer segments and coils.

    PAS-03-082

  • Si

    Si

    O

    O

    Si

    Si Si

    O

    O

    OH

    OH

    SiO

    Si

    O

    OO

    O OH

    R R

    R

    R

    R

    R

    R

    R = i-Butyl, Et

    T8T10

    T12

    Si

    Si

    O

    O

    Si

    Si

    Si

    Si

    O

    O

    O

    O

    SiO

    Si

    O

    OO

    OO

    R R

    R

    R

    R

    R

    R R

    R = Me, Et, i-Bu, Cp, Cy, i-Octyl, Ph

    POSS: Versatile Structures

    Closed Cage Open Cage

    PAS-03-082

    T8 =

  • Goals of POSS Work

    Understand how structure and functionality of POSS monomers affects polymer structure and properties

    Interact with synthetic chemists to characterize products and reaction intermediates

    Create materials with tailored properties.

  • Application Of Ion Mobility to POSS Characterization

    3-D Structural Information

    Ion Mobility Molecular Modeling

    Cross-Sectional Areas

    Structural differences withdifferent R groups

    Identify MixtureDistributions

    Structures ofIntermediates

    impurities insynthesis

    How structure changeswith size

    (POSS oligomers)How POSS attachesto polymers

  • AMBER Modifications for POSS Modeling

    New parameters for all Si bonds, angles, dihedrals, and torsions (adapted from Si and Si-X parameters obtained from polysiloxane work).

    Ref: H.Sun and D. Rigby, Spectrochimica Acta A, 1997, 53, 1301.Krueger, Et. al.,

    Atom charges for Si and O obtained from Gaussian calculations on model systems and x-ray structures; adjusted using AMBER RESP protocol.

    Starting structures generated in Hyperchem and imported into AMBER.

  • POSS Cross-Sections (2)

    168162167Ph4D4(OH)4

    153157154Cp4D4(OH)4

    216216212Vi12T12

    192193Vi10T10

    258252Cy8T8(OH)2

    248Cy7T7(OH)3

    215222Cy6T6(OH)2

    222225224Cy6T6

    Theory (Na+)

    MALDI -TOF(Na+) *

    x-rayPOSS System

    from Tim Haddad at ERC Inc., Air Force Research Laboratory similar values for H+ similar values for neutral

    Ref: J. Gidden, P.R. Kemper, E. Shammel, D.P. Fee, S Anderson, M.T. Bowers, Int. J. Mass Spectrom. 222 (2003) 63.

  • Ref: Erin S. Baker, Jennifer Gidden, David P. Fee, Paul R. Kemper, Stanley E. Anderson, and Michael T. Bowers, Int. J. Mass Spectrom. 2003, 227, 205-216.

  • 0 100 200 300 400 500 600 700 800 900 100011001200130014000.0

    0.2

    0.4

    Na+Sty8T8

    (Matrix Peaks)

    MALDI-TOF Mass Spectrum of Na+Sty8T8In

    tens

    ity (a

    rb. u

    nits

    )

    m/z

    Spectrum of Na+Sty8T8

    Na+Sty8T8

    Arrival Time Distribution

    Mass / charge

  • Experiment Complements Theory!

    TheoreticalStructures

    Cross-Sections ()

    Relative Energy (kcal/mol)

    Cro

    ss-S

    ecti

    on

    (

    2 )

  • Experiment Complements Theory!

    TheoreticalStructures

    Cross-Sections ()

    Relative Energy (kcal/mol)

    Cro

    ss-S

    ecti

    on

    (

    2 )

  • Experiment Complements Theory!

    TheoreticalStructures

    Cross-Sections ()

    Relative Energy (kcal/mol)

    Cro

    ss-S

    ecti

    on

    (

    2 )

  • Experiment Complements Theory!

    TheoreticalStructures

    Cross-Sections ()

    Relative Energy (kcal/mol)

    Cro

    ss-S

    ecti

    on

    (

    2 )

  • Na+Sty8T8 ATD

  • Na+Sty8T8 ATD

  • Na+Sty8T8 ATD

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