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  1. Conductive Films of Polysiloxane-Silver Composites Ragy Ragheb*, Dr. Jennifer Hoyt-Lalli, Dr. J. Mecham, Dr. J. Riffle Virginia Tech, Chemistry Dept. Blacksburg, VA August 2002

  2. Outline • Background/Objective • Synthesis of Polysiloxane series • 29Si NMR • 1H NMR • ATR • Synthesis of Silver-Filled composites • SEM • XPS • Preparation of Lap Shear Samples • Results • Conclusions • Future Work • Acknowledgements

  3. Objective • To achieve a series of functional polysiloxanes containing well-dispersed silver flakes • To determine a change in conductivity as a function of fatigue in silver filled polysiloxane composite • To monitor an decrease in conductivity as integrity of aircraft stress locations decreases. • Pendent electron donating groups result in specific interactions with metal fillers (Silver) • Complexation • Improve Dispersion Quality • Improve Adhesion • Optimize the percentage of polar functional groups that can complex with Silver particles. • Ensure proper dispersion between the polymer and the silver particles. • Understand “complexation”

  4. Synthesis of Random Trimethylsiloxy- Terminated Poly(dimethyl-co-methylhydrido)siloxane Prepolymers for Hydrosilation X=42.89 Y=39.87 2.00

  5. Hydrosilation Functionalization of Poly(dimethyl-co-methylhydrido)siloxanes to Yield Polyorganosiloxanes with Controlled Concentrations of Pendent Nitrile Moieties MW = 6443 g/mol % Nitriles = 25.5 Z=18.80 X=41.27 Y=13.78 2.00

  6. Hydrosilation Functionalization of Prepolymer monitored by 1H NMR T = 0 minutes T= 30 minutes

  7. Network Formation of Polyorganosiloxanes with Controlled Concentrations of Nitrilevia Hydrosilation Polysiloxane Networks with Controlled Concentrations of Nitrile Substitution

  8. Hydrosilation formation of networked organopolysiloxanes using Pt. Catalyst (5g Pt. Cat sol’n / 1 mole H) (cured at 80C) T= 0 hours T= 9 hours T= 21 hours %Trans/ Wavenumber cm-1

  9. Hydrosilation formation of networked organopolysiloxanes using Pt. Catalyst (2g Pt. Cat sol’n / 1 mole H) (cured at 80C) T= 0 hours T= 9 hours T= 21 hours %Trans / Wavenumber cm-1

  10. Synthesis of Silver-Filled Composites • STEP 1: Add Pt catalyst, crosslinking agent, then polymer • Manually mix the solution for 10-15 minutes, then degas in a vacuum chamber for 10-15 minutes. • STEP 2: Add silver particles • Mix in a vacuum chamber for 10-15 minutes, then degas in chamber 10-15 minutes. • STEP 3: Prepare thin films on glass slides for conductivity tests (Cured at 80°C overnight)

  11. Conductivity Analyses as a Function of the Volume Fraction of Ag

  12. Filler Distribution (FE-SEM) of Bulk Microcomposite Network10 Mol % 3-Cyanopropylmethylsiloxy- Substituted PolysiloxaneFilled with 22 vol % Ag Flake 500 X magnification 200k X magnification 500k X magnification Orientation of platelike Ag flakes observed from shear mixing

  13. Field-Emission SEM of a Silver Filled Polysiloxane Network 27 mole % CN with 28.8 vol % Ag EDS

  14. XPS of Silver Powder (1.0-5.0 microns)

  15. XPS of a Silver Filled Polysiloxane Network 27 mole % CN with 28.8 vol % Ag (fractured edge)

  16. XPS of a Silver Filled Polysiloxane Network 27 mole % CN with 28.8 vol % Ag (powder)

  17. Preparation of Lap Shear Samples • Clean polycarbonate sheets with isopropanol • Sand more than 1’ of some PC substrate • Sonicate in isopropanol for 5 minutes. • Clean with kimwipe and then rinse with isopropanol and wipe again . • Dry under vacuum at 80C for 30 minutes • Spread unfilled and filled samples on lapshear plates, covering 1 inch including copper tape. Gently press to remove any air pockets. • Cure them overnight at 80C.

  18. 27%CN (unfilled) 27%CN filled (28.8 vol % Ag)

  19. Conclusions / Future Work • Polysiloxane precursors to functionalization were prepared via ring opening equilibrations with controlled concentrations of methylhydridosiloxy units. • Polyorganosiloxanes with controlled concentrations of polar nitrile functional group were prepared via functionalization (hydrosilation) reactions with reactive prepolymers. • The hydrido groups of nitrile substituted polyorganosiloxanes were hydrosilated to yield lightly crosslinked elastomeric networks with varied concentrations of polarity • Stable microcomposite silver dispersions were prepared with 10%CN and 27%CN polyorganosiloxanes. These will be further dispersed with different volume fractions of silver to achieve the inflection point in electrical conductivity. • Could achieve a decently quantified resistance with 27%CN polymer on copper-taped glass slide. After further analysis of ATR data, will modify Pt. Catalyst amount and disperse series of silver-filled dispersions. • 54%CN might not have been optimally dispersed with various volume % Ag and proved to be too viscous of a polymer. • Will imbed newly formed silver filled polysiloxane networks into vinyl ester mold as another form of measuring conductivity as a function of applied fatigue.

  20. Dr. J. Riffle Dr. J. Hoyt Dr. Y. Lin Dr. J. Mecham Steve McCartney Frank Cromer Tom Glass Nanosonic, Inc. Riffle Group Acknowledgements

  21. Random poly(dimethyl-co-hydridomethyl-co-cyanopropylmethyl)siloxane Leaving a few hydridomethyl repeat units for further hydrosilation to form networks

  22. Effects of Nitrile Substitution on Tgs of Polyorganosiloxanes via DSC Mn Experimental Tgs (C ) 4460 3340 3410 10500 2nd heat thermograms 10C/minute

  23. Effect of Crosslinking on Tgs of Functionalized Polyorganosiloxane Networks

  24. Equilibrium Polymerizations provide Controlled MW Oligomers with Polydispersities of ~2

  25. Future Work

  26. 10%CN with 22.3 vol. % Ag, magnified

  27. Series of Polysiloxane

  28. 29Si NMR Analyses to Determine the Copolymer Compositions(8.5 mole% CN) Target MW: 4000 g/mol Actual MW: 5913 g/mol 62.01 5.85 2.00 6.30

  29. 27%CN filled (28.8 vol % Ag)

  30. Objective • To achieve a series of functional polysiloxanes containing well-dispersed silver flakes

  31. SEM of 10%CN with 22.3 vol. % Ag 500 X 5000 X Orientation of platelike Ag flakes observed from shear mixing

  32. Objective: Synthetic Approach • Successfully made the polysiloxane networks from previously made polymers. • Successfully dispersed silver with 10%CN and 27%CN. • Could achieve a decently quantified resistance with 27%CN polymer on copper-taped glass slide. • 54%CN might not have been optimally dispersed with various volume % Ag and proved to be too viscous of a polymer.

  33. Synthesis of Polysiloxane Networks

  34. Karstedt’s Catalyst and the Hydrosilation Catalytic Cycle CH2=CH-Si(CH3)2-O-Si(CH3)2-CH=CH2 + H2PtCl6 Karstedt’s Catalyst side reaction to note: Si-H + H2O + Pt Si-OH + H2

  35. Poly(dimethyl-co-methylhydrido)siloxanes with Controlled Mol Fractions of Methylhydridosiloxy- Units Analyzed via Quantitative 29Si NMR • Mn • Random Microstructure • Chemical Composition Mn = 4100 17% 46 10 MHH MDH MHD MDD Mn = 2700 45% 21 17 Mn = 2200 72% 9 23