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    Molecular Nanotechnology

    Richard Feynman s talk in 1959, entitled There's Plenty of Room at the Bottom .

    K Eric Drexlers 1986 book Engines of

    Creation: The Coming Era of Nanotechnology .

    Top Down Approach IC, MEMS, etc. Bottom Up Approach Molecular Machine, Ribosome, DNA, Cell

    Membrane, etc.

    An Overview

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    Molecular Nanotechnology

    The next big thingis really SMALL

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    About Complexity

    Small Change in the Force Field orthe Boundary Condition of theInteracting Molecules could Resultin Completely Different Results.

    Self-assembly of gold-polymer nanorodsresults in a curved structure.Chad Mirkin, Northwestern University

    Self-Assembly: Reversibleprocesses in which pre-existing parts or disorderedcomponents of apreexisting system formstructures of patterns.

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    Irreducible Complexity

    "a single system which is composed of several interacting parts that contribute to the basic function, and where theremoval of any one of the parts causes the system to effectivelycease functioning". (Michael Behe, Molecular Machines: Experimental Support for the Design Inference )

    Solution:

    Molecular Interaction DataBase

    Computer Simulation:Molecular Dynamics Simulation

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    Molecular Dynamic Simulation

    (a) Molecular Dynamics simulation"snapshot" of a silicate-surfactant-

    polystyrene nanocomposite. (b) The

    corresponding number density of carbonatoms as a function of distance.

    Schematic of the polymer layeredsilicate nanocomposite (PLSN)morphologies: (a) intercalated and (b)exfoliated.

    D.B. Zax, D.-K. Yang, R.A. Santos, H. Hegemann, E.P. Giannelis and E.

    Manias. J. Chem. Phys., 112 , 2945, (2000).

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    Polymer Nanocomposites (PNC)

    ApplicationsHeat-resistant materialsLight weight and high strength structuralmaterials

    Electrical package, conductive polymers.Barrier PropertiesCorrosion resistant, coating or structureElectro-magnetic field shieldingSelective photo sensitivity, coatings, etc

    It is estimated that widespread use of PNCs by carmanufacturers could save over 1.5 billion liters of gasolineannually and reduce CO 2 emissions by nearly 10 billionpounds!

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    Polymer Nanocomposies Popular Nano-reinforcements

    BuildingBlocks of the NanoAge

    Clay

    Other Synthetic Materials

    POSS

    Graphite

    Carbon Nanotube,Bukcyball

    Cellulose

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    Polymer Nanocomposies Surface Modification, Dispersion

    Ion exchange for clays

    Addition reaction on CNTs (fullerenes)

    Acidification, fluorination, etc. in order to attach differentfunctional groups onto nano reinforcement surface to improvedispersion as well as reactivity with the matrix structuremorphology change & tailoring of interface

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    Focus : Carbon Nanotube Functionalization

    R 1 NHCH 2 C(=O)OH + R 2 CH=O

    DMF, 130 o C 120 h

    N H 2 C C H

    R 1 R 2

    + _ - H 2 O , C O 2

    N

    R 2

    R 1

    x

    SWNTs S W N T

    R 1 = - C H 2 ( C H 2 ) 6 C H 3 , - C H 2 C H 2 O C H 2 C H 2 O C H 2 C H 2 O C H 3

    R 2 = H , O C H 3 ,

    ROC(=O)N 3 + SWNT

    - N 2

    160 oCODCB

    SWNT [>NC(=O)OR]

    R = tert-Butyl, Ethyl, oligoether groups

    Azomethine Ylides M. Prato, A. Hirsch et al., 2001

    R

    N2+BF4

    -

    R

    NH2

    RSWNT

    xBu4N

    +BF4-

    CH 3CN

    SWNTs, -1 V (CH 3)2CHCH 2CH 2ONO

    SWNTs

    ODCB / CH 3CN, 2:1

    65 oC

    R = tert-Butyl, halogen, COOH, NO 2, COOH, CO 2CH3 etc.

    Aryl Diazonium Salts, J. Tour et al., 2001

    [F] x-SWNTsF2 /H 2

    SWNTsheat

    SWNTs + RC(=O)OO(=O)CRheat

    - CO 2SWNT[R]x-

    R = C 11H23, C6H5, CH2CH2COOH

    FluorinationJ. L. Margrave et al., 1998

    Acyl PeroxidesV.N.Khabashesku et al., 2002

    NitrenesA. Hirsch et al., 2001, 2 003

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    Polymer Nanocomposies Network Formation

    POSS

    Carbon Nanotubes

    Controlling FactorsProperties of theMatrix

    Properties of theNano-reinforcementInterface Properties

    of the Nanocomposites

    Interaction betweenReinforcement andMatrix during Loading(Thermal, Mechanical,Electronical, etc.)

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    Conflicting Property Reports

    Conflicts Result from Differences in Matrix Polymer Repeating Unit

    Relative Mobility of Nano-reinforcement Compared with Matrix

    Degree of Crosslinking

    Polymerization Mechanism

    Nano-reinforcement

    Surface Treatment

    Degree of Dispersion

    etc.

    DeconvolutionSimple Model System

    Experimental Condition

    Raw Materials Selection

    Molecular Dynamics

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    the Future

    Properties Design

    Microscopic Morphology Control

    Optimum Interface Design

    Mechanosynthesis of Polymer Chains

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    MWCNT/Epoxy Nanocomposites

    Structure Change

    Morphology Change

    Increased Mobility

    Thermal Mechanical Properties

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    Preparation of Nanocomposites

    MWCNT (40-60nm,10 m)

    A- CNT PGE-CNT EPON-CNT

    Bulk Sample

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    Mono-epoxy: PGE

    PGE-CNT

    Di-epoxy: Epon 828

    Epon-CNT

    A-CNT

    Pure-CNT

    Auad, M. L. et al, J. J APPL POLYM SCI 66: (6) 1997

    MWCNT/Epoxy Nanocomposites

    Surface Treatment (Continued)

    A B

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    Solubility Change After Modification

    Solubility change in water

    Pure-CNT A-CNT PGE-CNT EPON-CNT

    Increasing solubility in THF

    Pure-CNT A-CNT PGE-CNT EPON-CNT

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    FTIR Spectrum of Treated CNTs

    2920,2850 cm-1C-H Stretch

    1710 cm-1

    Carboxylic group

    1250 cm-1Aromatic Ether

    760 cm-1Epoxy ring

    12 Band

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    CNTs/ Epoxy Composites

    Solvent Evaporation

    A-CNT

    PGE-CNT

    Epoxy-CN T

    0.9wt%

    0.7wt%

    0.51wt%

    Functionalized CNTdispersed in THF

    1wt%

    Epoxy (EPON 828)

    DMAP (initiator)(-4dimethylamino)pyridine

    Crosslinking Reaction

    Nanocomposites

    Williams et al. Macromol.Mat. and Eng. 289, 315, 2004

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    10 m

    Morphology: SEM

    MatrixEPON 828

    10 m

    A-CNT

    10 m

    PGE-CNT

    10 m

    Pure-CNT

    1wt% CNT

    10 m

    Epon-CNT

    CNTs agglomerations

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    DMA Test @ 1wt% Treated CNTs

    40 60

    3000

    4000

    S t o r a g e M o d u l u s ( M P a )

    Temperature (oC)

    Pure EpoxyA-CNT Epoxy

    PGE-CNT EpoxyEPON-CNT Epoxy

    140 160 180

    0

    1000

    S t o r a g e M o d u l u s ( M P a )

    Temperature (oC)

    Pure EpoxyA-CNT EpoxyPGE-CNT EpoxyEPON-CNT Epoxy

    40 60 80 100 120 140 160 180 200 220 240

    0

    50

    100

    150

    200

    250

    300

    350

    L o s s M o d u l u s ( M P a )

    Temperature (oC)

    EpoxyA-CNT compositePGE-CNT compositeEPON-CNT composite

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    MD Simulation of SWCNT&EPON Mixture

    Amorphous unit cell, orthorhombic, (7,0) swCNTs dispersed in Epon828

    600,000 steps (600ps), NVT ensemble (298K), 1.4 g/cc, 14.9V%, 69W%

    0 2 4 6 8 10

    0.0

    0.2

    0.4

    0.6

    0.8

    1.0

    1.2

    1.4

    1.6

    Pair Corelation Function (cnt-cnt;o-cnt)

    Blue: 50-150 psRed: 500-600 ps

    G a b

    ( r )

    r (Angstrom)

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    Stress-Strain Curve/Elastic Constants

    Pair Distribution Functions

    Tg

    Diffusive Behavior

    IR Spectrum & Radiation Scattering Function (X-Ray, Neutron)

    Concentration Profiles

    Temperature Profile

    Orientation Correlations

    What to simulate in MD?

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    CONCLUSIONS

    Well dispersed nano-fillers would have a confinementeffect for the matrix, which leads to the improvement of Tg.

    The mobility of the polymer chain & the mobility of thenano-fillers dominates the properties of nanocomposites.

    Different interfacial bonding would lead to variedimprovement for the glass transition temperature.

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    Future Work

    Exploring the toughening mechanism of CNT polymer nanocomposites, focus on thermal mechanical properties.

    Single walled carbon nanotube reinforced shape memory PU.

    Building a MD model for thermoset polymers reinforced withrandomly oriented SWCNTs/ modified SWCNTs.

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    Thank You

    Questions?

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    MD ABC

    Molecular Dynamics Simulation

    Ideal length and time scale Bridging the molecular level with R EAL WORLD MATERIALS

    Materials Structure Characterization and Property Prediction

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    Molecular Dynamics Simulation

    Initiation:

    Definition of Simulation Cell {R (N,V,E)}

    * Periodical Boundary Condition

    * Minimum Image Convention

    Energy minimization (non crystalline)

    Assignment of initial velocity {v (N,V,E)}

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    Force Fields: Non-bond Covalent Bond

    Force = Mass*Acceleration

    The force on each atom is related to the partial derivative of potential energy over

    the position vector of the atom.

    We can derive the ensemble of {R} and {v} of the system after minute time step t

    Thus, we can numerically decide the trajectory of the system over time.

    Molecular Dynamics Simulation

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    Equilibrium:

    Allow sufficient number of time steps to be calculated so that the system reachequilibrium --- thermal dynamic data (such as Total Energy, Potential Energy, Cv) no

    longer change or oscillate around the equilibrium value. )

    Molecular Dynamics Simulation

    Data Collection: The trajectory average of the structural or thermal dynamic property over

    time will be the simulated value.

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    D

    1 3 8 2

    . 7

    1 6 3 5

    . 8

    CNT

    -0.00

    0.01

    0.02

    0.03

    0.04

    A b s o r b a n c e

    8 0 6

    . 5 1 0 2 4

    . 4

    1 1 0 3

    . 7

    1 2 5 9

    . 5

    1 3 7 9

    . 9

    1 4 5 7

    . 5

    1 5 5 3

    . 7

    1 6 3 5

    . 8

    1 7 0 9

    . 5

    2 3 6 0

    . 2

    2 8 5 6

    . 0

    2 9 2 4 . 8

    3 4 2 9

    . 3

    PGE-CNT

    -0.0

    0.1

    0.2

    0.3

    A b s o r b a n c e

    8 1 7

    . 8

    8 7 7

    . 2

    1 0 3 0

    . 1

    1 1 1 0

    . 4

    1 1 8 2

    . 9

    1 2 5 6

    . 6 1 3 7 9 . 9

    1 4 5 1

    . 8

    1 5 6 7

    . 9 1 6 3 3

    . 0

    1 7 0 9

    . 5

    2 3 6 0

    . 2

    2 8 5 0

    . 3

    2 9 2 2

    . 0EPON-CNT

    0.000

    0.005

    0.010

    0.015

    0.020

    A b s o r b a n c e

    100015002000250030003500

    Wavenumbers (cm-1)