Synthesis of Polystyrene-Silica Composite Particles via One-Step Nanoparticle-Stabilized Emulsion Polymerization          ...
2<br />Polymer Composites<br />Wide applications<br />Automotives<br />Aircrafts<br />Electronic devices<br />Sports equip...
3<br />Polymer Composites<br />Polymer<br />Traditional <br />Composites<br />+<br />Inorganic Particles<br />NewPolymer C...
4<br />One-Step Nanoparticle-Stabilized Emulsion Polymerization<br />nanoparticle-stabilized<br />emulsion polymerization<...
5<br />electrostatic<br />attractions<br />cationic<br />initiators<br />nanoparticles<br />( - )<br />nonionic<br />initi...
6<br />Objectives<br />Synthesize core-shell structured polystyrene-silica composite particles by emulsion polymerization ...
Materials<br />Monomer: Styrene<br />99.9 %, Fisher<br />Continuous phase: Water<br />HPLC, AcroOrganics<br />Nanoparticle...
8<br />Why Initiator VA-086?<br />No success has been reported in surfactant-free emulsion polymerization of styrene<br />...
9<br />Synthesis<br />Styrene in water emulsion stabilized by silica nanoparticles<br />Composite particles<br />N2<br />A...
10<br />Particle Morphology and Size Distribution(TEM, SEM, EDX, and DLS)<br />VA-086: 0.06 g<br />Styrene: 8 mL<br />IPA-...
11<br />Silica Content(TGA)<br />Composite particles<br />200 nm<br />HF treated particles<br />†A. Schmidet al., Chem. Ma...
12<br />Glass Transition Temperature(DSC)<br />Polymer immobility at silica surface<br />Attractive interaction<br />Tg in...
13<br />Particle Size and Surface Coverage<br />24 h<br />11 h<br />3 h<br />Initiator/monomer<br />0.83 wt%<br />2.5 wt%<...
14<br />Conclusions<br />Polystyrene-silica core-shell structured composite particles with silica content up to 20 wt% wer...
15<br />Acknowledgements<br />The Department of Chemical Engineering, the Department of Chemistry, and the Imaging Center ...
Thanks!<br />Questions?<br />
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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 Physical Society March Meeting, March 2009

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

  1. 1. Synthesis of Polystyrene-Silica Composite Particles via One-Step Nanoparticle-Stabilized Emulsion Polymerization <br />Huan Ma and Lenore L. Dai<br />Chemical Engineering <br />Arizona State University<br />AIChE Annual Meeting 2009<br />
  2. 2. 2<br />Polymer Composites<br />Wide applications<br />Automotives<br />Aircrafts<br />Electronic devices<br />Sports equipments<br />Paints<br />Food packages<br />…<br />Advanced properties<br />Mechanical<br />Thermal<br />Electrical<br />Optical<br />…<br />
  3. 3. 3<br />Polymer Composites<br />Polymer<br />Traditional <br />Composites<br />+<br />Inorganic Particles<br />NewPolymer Composites<br />Core-Shell Composite Particles<br />How About?<br />Traditional Polymer Composites vs. Core-Shell Composite Particles<br />
  4. 4. 4<br />One-Step Nanoparticle-Stabilized Emulsion Polymerization<br />nanoparticle-stabilized<br />emulsion polymerization<br />Inorganic Particles<br />Pickering Emulsions<br />(using solid nanoparticles as stabilizer)<br />
  5. 5. 5<br />electrostatic<br />attractions<br />cationic<br />initiators<br />nanoparticles<br />( - )<br />nonionic<br />initiators<br />x<br />Synthesis of Polystyrene-SilicaComposite Particles<br />Emulsion polymerization<br />No success has been reported using nanoparticles as the sole stabilizing agent<br />Dispersion polymerization<br />Solely stabilized by silica nanoparticles<br />Cationic initiator AIBA – core-shell structure (up to 29 % silica)<br />Nonionic initiator AIBN – poor coverage (up to 1.1 % silica)<br />Really impossible???<br />A. Schmidet al., Chem. Mater.2007, 19, 2435-2445<br />
  6. 6. 6<br />Objectives<br />Synthesize core-shell structured polystyrene-silica composite particles by emulsion polymerization with a nonionic initiator, using silica nanoparticles as the sole stabilizing agent<br />Characterize particle size, morphology, and composition<br />Track the change of particle size and surface coverage with reaction time at various initiator concentrations<br />
  7. 7. Materials<br />Monomer: Styrene<br />99.9 %, Fisher<br />Continuous phase: Water<br />HPLC, AcroOrganics<br />Nanoparticle: IPA-ST <br />10-15 nm silica nanoparticles dispersed in isopropanol<br />30-31 wt%, Nissan Chemicals<br />Initiator: VA-086<br />Azobis[2-methyl-N-(2-hydroxyethyl)propionamide]<br />Water-soluble<br />Nonionic<br />98 %, Wako Chemicals<br />7<br />
  8. 8. 8<br />Why Initiator VA-086?<br />No success has been reported in surfactant-free emulsion polymerization of styrene<br />Synthesis without silica nanoparticles<br />Opaque product (low conversion)<br />No particle formation was observed<br />The initiator VA-086 has little effect on stabilizing an emulsion polymerization system<br />Silica nanoparticles are the only source of stabilizers when present<br />The system do not contain surfactants nor auxiliary co-monomers<br />200 nm<br />
  9. 9. 9<br />Synthesis<br />Styrene in water emulsion stabilized by silica nanoparticles<br />Composite particles<br />N2<br />Add VA-086 solution<br />At least<br /> 3 h<br />70 oC<br />Wash*<br />Characterization<br />* Two centrifuging-redispersing cycles: centrifuge at 7000 rpm for 5 minutes at 23 oC and redisperse by manual shaking<br />
  10. 10. 10<br />Particle Morphology and Size Distribution(TEM, SEM, EDX, and DLS)<br />VA-086: 0.06 g<br />Styrene: 8 mL<br />IPA-ST: 20 g<br />(dried silica 6 g; 2-propanol 14 g)<br />Water: 52.5 g<br />Reaction time: 5 h<br />200 nm<br />200 nm<br />2 µm<br />
  11. 11. 11<br />Silica Content(TGA)<br />Composite particles<br />200 nm<br />HF treated particles<br />†A. Schmidet al., Chem. Mater.2007, 19, 2435-2445<br />The nanoparticles are thermodynamically favorable to self-assemble at the liquid-liquid interfaces, even in the absence of electrostatic interactions<br />200 nm<br />
  12. 12. 12<br />Glass Transition Temperature(DSC)<br />Polymer immobility at silica surface<br />Attractive interaction<br />Tg increase<br />Experimental results:<br />Composite particles: Tg = 103.8±0.2oC<br />HF treated particles: Tg = 100.7±0.0 oC<br />Reference results:<br />Depending on the silica nanoparticle source, either slightly elevated Tg or depressed Tg was observed in polystyrene-silica composite particles<br />M. J. Percy et al., Langmuir2004, 20, 2184-2190.<br />
  13. 13. 13<br />Particle Size and Surface Coverage<br />24 h<br />11 h<br />3 h<br />Initiator/monomer<br />0.83 wt%<br />2.5 wt%<br />4.2 wt%<br />
  14. 14. 14<br />Conclusions<br />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<br />Silica nanoparticles act as the sole stabilizer during the polymerization, following the same mechanism in solid-stabilized emulsions<br />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<br />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<br />The surface coverage also changes with the reaction time and the initiator concentration, but the underlying mechanism is still not fully understood<br />
  15. 15. 15<br />Acknowledgements<br />The Department of Chemical Engineering, the Department of Chemistry, and the Imaging Center at Texas Tech University<br />NSF funding (CBET-0918282)<br />
  16. 16. Thanks!<br />Questions?<br />

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