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1.	Synthesis of Polystyrene-Silica Composite Particles via One-Step Nanoparticle-Stabilized Emulsion Polymerization
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1. Synthesis of Polystyrene-Silica Composite Particles via One-Step Nanoparticle-Stabilized Emulsion Polymerization

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American Institute of Chemical Engineers Annual Meeting, November 2009 …

American Institute of Chemical Engineers Annual Meeting, November 2009
American Physical Society March Meeting, March 2009

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  • 1. Synthesis of Polystyrene-Silica Composite Particles via One-Step Nanoparticle-Stabilized Emulsion Polymerization
    Huan Ma and Lenore L. Dai
    Chemical Engineering
    Arizona State University
    AIChE Annual Meeting 2009
  • 2. 2
    Polymer Composites
    Wide applications
    Automotives
    Aircrafts
    Electronic devices
    Sports equipments
    Paints
    Food packages

    Advanced properties
    Mechanical
    Thermal
    Electrical
    Optical

  • 3. 3
    Polymer Composites
    Polymer
    Traditional
    Composites
    +
    Inorganic Particles
    NewPolymer Composites
    Core-Shell Composite Particles
    How About?
    Traditional Polymer Composites vs. Core-Shell Composite Particles
  • 4. 4
    One-Step Nanoparticle-Stabilized Emulsion Polymerization
    nanoparticle-stabilized
    emulsion polymerization
    Inorganic Particles
    Pickering Emulsions
    (using solid nanoparticles as stabilizer)
  • 5. 5
    electrostatic
    attractions
    cationic
    initiators
    nanoparticles
    ( - )
    nonionic
    initiators
    x
    Synthesis of Polystyrene-SilicaComposite Particles
    Emulsion polymerization
    No success has been reported using nanoparticles as the sole stabilizing agent
    Dispersion polymerization
    Solely stabilized by silica nanoparticles
    Cationic initiator AIBA – core-shell structure (up to 29 % silica)
    Nonionic initiator AIBN – poor coverage (up to 1.1 % silica)
    Really impossible???
    A. Schmidet al., Chem. Mater.2007, 19, 2435-2445
  • 6. 6
    Objectives
    Synthesize core-shell structured polystyrene-silica composite particles by emulsion polymerization with a nonionic initiator, using silica nanoparticles as the sole stabilizing agent
    Characterize particle size, morphology, and composition
    Track the change of particle size and surface coverage with reaction time at various initiator concentrations
  • 7. Materials
    Monomer: Styrene
    99.9 %, Fisher
    Continuous phase: Water
    HPLC, AcroOrganics
    Nanoparticle: IPA-ST
    10-15 nm silica nanoparticles dispersed in isopropanol
    30-31 wt%, Nissan Chemicals
    Initiator: VA-086
    Azobis[2-methyl-N-(2-hydroxyethyl)propionamide]
    Water-soluble
    Nonionic
    98 %, Wako Chemicals
    7
  • 8. 8
    Why Initiator VA-086?
    No success has been reported in surfactant-free emulsion polymerization of styrene
    Synthesis without silica nanoparticles
    Opaque product (low conversion)
    No particle formation was observed
    The initiator VA-086 has little effect on stabilizing an emulsion polymerization system
    Silica nanoparticles are the only source of stabilizers when present
    The system do not contain surfactants nor auxiliary co-monomers
    200 nm
  • 9. 9
    Synthesis
    Styrene in water emulsion stabilized by silica nanoparticles
    Composite particles
    N2
    Add VA-086 solution
    At least
    3 h
    70 oC
    Wash*
    Characterization
    * Two centrifuging-redispersing cycles: centrifuge at 7000 rpm for 5 minutes at 23 oC and redisperse by manual shaking
  • 10. 10
    Particle Morphology and Size Distribution(TEM, SEM, EDX, and DLS)
    VA-086: 0.06 g
    Styrene: 8 mL
    IPA-ST: 20 g
    (dried silica 6 g; 2-propanol 14 g)
    Water: 52.5 g
    Reaction time: 5 h
    200 nm
    200 nm
    2 µm
  • 11. 11
    Silica Content(TGA)
    Composite particles
    200 nm
    HF treated particles
    †A. Schmidet al., Chem. Mater.2007, 19, 2435-2445
    The nanoparticles are thermodynamically favorable to self-assemble at the liquid-liquid interfaces, even in the absence of electrostatic interactions
    200 nm
  • 12. 12
    Glass Transition Temperature(DSC)
    Polymer immobility at silica surface
    Attractive interaction
    Tg increase
    Experimental results:
    Composite particles: Tg = 103.8±0.2oC
    HF treated particles: Tg = 100.7±0.0 oC
    Reference results:
    Depending on the silica nanoparticle source, either slightly elevated Tg or depressed Tg was observed in polystyrene-silica composite particles
    M. J. Percy et al., Langmuir2004, 20, 2184-2190.
  • 13. 13
    Particle Size and Surface Coverage
    24 h
    11 h
    3 h
    Initiator/monomer
    0.83 wt%
    2.5 wt%
    4.2 wt%
  • 14. 14
    Conclusions
    Polystyrene-silica core-shell structured composite particles with silica content up to 20 wt% were successfully synthesized by emulsion polymerization using nonionic initiator VA-086
    Silica nanoparticles act as the sole stabilizer during the polymerization, following the same mechanism in solid-stabilized emulsions
    When the silica/monomer ratio is increased from 0.83 wt% to 2.5 wt%, the particle size at 24 hour reaction time decreases for a fixed monomer amount, probably due to a larger number of nuclei at the initial stage of polymerization
    Further increasing the initiator/monomer ratio to 4.2 wt% does not continually decrease the particle size, which might be limited by stabilization provided by a fixed concentration of silica nanoparticles
    The surface coverage also changes with the reaction time and the initiator concentration, but the underlying mechanism is still not fully understood
  • 15. 15
    Acknowledgements
    The Department of Chemical Engineering, the Department of Chemistry, and the Imaging Center at Texas Tech University
    NSF funding (CBET-0918282)
  • 16. Thanks!
    Questions?