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Plasma polymers for reaching reversible metal / elastomer adhesion

Plasma polymers for reaching reversible metal / elastomer adhesion. Institut de Chimie des Surfaces et Interfaces UPR 9069 15 rue Jean Starcky, 68057 Mulhouse. Frederic SIFFER. Presentation agenda. 1 Background – Diels-Alder reaction, plasmas

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Plasma polymers for reaching reversible metal / elastomer adhesion

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  1. Plasma polymers for reaching reversible metal / elastomer adhesion Institut de Chimie des Surfaces et Interfaces UPR 9069 15 rue Jean Starcky, 68057 Mulhouse Frederic SIFFER

  2. Presentation agenda • 1Background – Diels-Alder reaction, plasmas • 2 Chemometric investigation of the effect of the process parameters during pulsed plasma polymerization of maleic anhydride • 4Synthesis of bi-functional molecules for interfacial Diels-Alder reactions • 5Following Diels-Alder reaction kinetics in solution on dienophile functionalized substrates • 6Interfacial Diels-Alder reaction between 2 substrates correctly functionalized • 7 Conclusion & perspectives

  3. Background Plasma polymer functionalized substrate Interfacial chemistry A B Understand and control adhesion properties

  4. Background Diene CH2 C C C C C C H C CH2 H C C CH2 C C C R C H H C H H C H C C R Dienophile C R H H Diels-Alder reaction overview Transition state Concerted reaction New C-C bonds formed

  5. Background Goal : Control adhesion properties between 2 surfaces functionalized by plasma polymerization via Diels-Alder reaction Retro Diels-Alder Diels-Alder

  6. Plasma… Gas inlet Electrode Ions Electrons Recombinaison Molecules Reactions Ionisation Ions -molecules Radicals Optical Emission sheath Substrate Electrode Vacuum

  7. Plasma… Excitations Dissociations Ionisations Recombinaisons Radiations Neutrals Ionic species sheath Boundary Acceleration Diffusion Desorption Bombardement Migration, Dissociation, Reaction Adsorption, Surface Substrate

  8. Plasma… Bicyclic polymerization Plasma excitation H. Yasuda. Plasma Polymerization, Academic Press, 1985

  9. Plasma… deposition modification deposition ablation Plasma on Plasma off UV Electrons Molecules Species density Radicals Ions Substrate Substrate Vitesse de déposition Power (W) Impulsion length (10-3 s – 10-6 s)

  10. Plasma polymerization setup Schéma simplifié du mécanisme de polymérisation R/R’ = -COOH -CH2OR -C=O -CH3 -OH … R.F. pulsées 30 min High reactivity Pressure gauge Valve Copper turns O-ring Gas Fittings Substrate Maleic anhydride Monomer Pump Glass plate R.F. generator Matching 13,56 MHz box Liquid nitrogen

  11. Pulsed plasma polymerization ton Puissance Pp Variation of ton toff Pp toff Variation of plasma polymer properties Monitoring RF signal via an oscilloscope • Desired plasma coating properties : • Highest concentration of maleic anhydride functionalities incorporated in polymer • - Low roughness • - Ultra thin plasma polymer coating Need to optimize plasma parameters

  12. Use of chemometric tools Area of interest Domain of variation of plasma parameters for DOE study Domain of variation of refined parameters for central composite design

  13. Plasma coating properties AFM image - Phase z=3° - 2μm x 2μm Optimized conditions : 5W, 25µs on-time, 1200µs off-time C=O sym. vibration C=O antisym. vibration C 1s Anhydride groups C-O-C elongation Elongation cycles anhydride conjugués Conjugated anhydrides – cycle elongation Binding energy (eV) Wavenumber (cm-1) XPS IRRAS AFM Anhydride group retention : 32% Film thickness : 15 nm Roughness :~ 0.2 nm

  14. Influence of substrate on plasma coating morphology Silicon wafer Sputtered gold Mirror finish aluminum EPDM Model substrates Industrial substrates Surface morphology prior to plasma polymerization Pulsed plasma polymerization Surface morphology prior to plasma polymerization Surface morphology after plasma coating deposition

  15. Plasma coating functionalization Aminolysis reaction Functionalization R = Diene or Dienophile Functionalized plasma coating

  16. Bifunctional molecules Diene Dienophile No commercial availability Available commercially SYNTHESIS

  17. Synthesis of the bifunctional diene Plasma polymer thin film Au Targeted molecule : F. Siffer, V. Roucoules, M.-F. Vallat, A. Defoin, “Synthesis of new functionalized cyclopentadienes to reach reversible bonding between two substrates”, Synthesis,2008 (4), 515-518.

  18. Plasma coating functionalization a) Plasma coating b) Gas phase 120°C – 2 hrs under vacuum Wavenumber (cm-1) c) Plasma coating d) Plasma coating Plasma coating functionalized with dienophile groups

  19. Diels-Alder reaction Newly created C-C bonds CH2 C C Au Au Au Diene C C C C H CH2 C C H C C CH2 C C C H C H H H C H C C Dienophile C H H Concerted reaction : Transition state

  20. Reaction kinetics of interfacial Diels-Alder Si [(triméthylsilyl)methyl]cyclopentadiene Pulsed plasma polymer Pulsed plasma polymer Diene used for this study CPdSi

  21. Following Diels-Alder reaction kinetics q Wettability measurements: 89 84 79 74 Advancing contact angle (°) 69 294 K 308 K 64 318 K 328 K 278 K 288 K 59 0 1000 2000 3000 4000 5000 6000 Time (s)

  22. Functional group density Plasma polymer Plasma polymer Cassie equation : Cos θexperimental = calkene . Cos θalkene + cbicyclo . Cos θbicyclo calkene θalkene = 60° cbicyclo calkene Cyclohexane θexpérimental cbicyclo θbicyclo = 87°

  23. Following Diels-Alder reaction kinetics Polymère plasma 0,9 293 K 0,8 308 K 0,7 328 K 0,6 0,5 0,4 Si/N ratio (area under peak) 0,3 0,2 0,1 0 0 1000 2000 3000 4000 5000 6000 Time (s) XPS measurements – following Si/N ratio CPS Si/N = 1 when all dienophile groups have undergone a Diels-Alder reaction Binding energy (eV)

  24. Interfacial Diels-Alder reaction between solid substrates Is the Diels-Alder reaction effective between 2 functionalized substrates Functionalization with diene groups Substrate 1 aluminum Plasma polymerization Substrates assembled In a curing press Substrate 2 aluminum or rubber Functionalization with dienophile groups

  25. Disponibility of dienophile groups Aluminum Aluminum Crosslinking reaction Press 170ºC - 40min – 3 MPa 1st step : verify that dienophile groups immobilized on aluminum are available to react during EPDM peroxide cure EPDM EPDM Imide Amide Dicumyleperoxyde Aluminum Aluminum Aluminium

  26. Disponibility of dienophile groups EPDM Aluminum Interfacial fracture energy 180 degree peel tests Amide 1200 180 degrees 20 mm/min Imide (vacuum) 5 mm/min Imide (atmosphere) 1000 Reference 800 W180 (J/m²) 600 EPDM cohesion energy 400 20 mm/min 5 mm/min 200 0 0 20 40 60 80 100 120 Peeled length (mm) -200 Dienophile groups seem to be available for interfacial reaction

  27. Analysis of peeled substrates q • Bare EPDM : • A: 103º R: 45º Wettability measurements Contact angle (after peel test) Advancing:103º ± 2º Receding :42º ± 2º EPDM Cohesive fracture located in EPDM Advancing:100º ± 2º Receding :35º ± 2° Aluminum

  28. Interfacial Diels-Alder reaction between functionalized EPDM / aluminum EPDM Substrates assembled in a curing press for different conditions of pressure, time and temperature Pulsed plasma polymer Pulsed plasma polymer 30°C – 70°C 30min – 120 min 0,08 MPa – 0,32 MPa Pulsed plasma polymer Pulsed plasma polymer EPDM DOE performed to optimize assembling conditions

  29. Interfacial Diels-Alder reaction between functionalized EPDM / aluminum Aluminum EPDM Peel energy between 2 dienophile functionalized substrates Peel energy between 2 substrates respectively functionalized with diene and dienophile groups Peeled length (mm) No interfacial bond formation Interfacial Diels-Alder seem to proceed !

  30. Interfacial Diels-Alder reaction – AFM images of aluminum substrate before and after peel test Pelage 180° EPDM ALUMINIUM Phase image Height image Ra = 18.74 nm Plasma coated aluminum substrate (prior to peel test) Aluminum substrate after peel test Phase image Height image Ra = 62.32 nm

  31. Interfacial Diels-Alder reaction – AFM images of EPDM substrate before and after peel test 180° peel test EPDM ALUMINIUM Phase image Height image Ra = 13.9 nm Bare EPDM Plasma coated EPDM (prior to peel test) Height image Ra = 60.6 nm Phase image EPDM substrate after peel test Height image Ra = 16.1 nm Phase image

  32. Analysis of peeled substrates Contact angles (after peel test) Advancing:100º ± 2º Receding :40º ± 2º EPDM Advancing:103º ± 2º Receding :42º ± 2° Aluminum Bare EPDM : • A: 103º R: 45º q Wettability measurements Cohesive fracture located in EPDM

  33. Retro Diels-Alder Diels-Alder reaction seem to proceed at interface Is the reaction reversible Reversibility test : 180 degree peel test performed while heating sample Ambient temperature Peeled length (mm)

  34. Conclusion - perspectives Plasma coating strongly adheres to EPDM, Al Substrates easily functionalized with diene, dienophile groups Solid-state Diels-Alder reaction seem to proceed Indication that Retro Diels-Alder undergoes at high temperature Interfacial reaction can be extended to other types of substrates Diels-Alder Retro Diels-Alder

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