1. April 19 th 2011 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. April 19 th 2011 2  1 Background – Diels-Alder reaction, plasmas  2 Chemometric investigation of the effect of the process parameters during pulsed plasma polymerization of maleic anhydride  4 Synthesis of bi-functional molecules for interfacial Diels-Alder reactions  5 Following Diels-Alder reaction kinetics in solution on dienophile functionalized substrates  6 Interfacial Diels-Alder reaction between 2 substrates correctly functionalized  7 Conclusion & perspectives Presentation agenda

3. April 19 th 2011 3 Plasma polymer functionalized substrate Understand and control adhesion properties B ABackground Interfacial chemistry

4. April 19 th 2011 4Background Diels-Alder reaction overview C C C C CH 2 C C H H H R C C H H H R Dienophile C C C C Diene Transition state C C C C CH 2 C C H H H R New C-C bonds formed Concerted reaction

5. April 19 th 2011 5Background Diels-Alder Retro Diels-Alder Goal : Control adhesion properties between 2 surfaces functionalized by plasma polymerization via Diels-Alder reaction

6. April 19 th 2011 6Plasma… Substrate Electrode Gas inlet Vacuum Electrode Electrons Ions Molecules Recombinaison Ionisation Optical Emission Radicals Reactions Ions -molecules sheath

7. April 19 th 2011 7 Substrate Excitations Ionisations Radiations Dissociations Recombinaisons Surface NeutralsIonic species Migration, Adsorption, Dissociation,Reaction sheath Bombardement Diffusion Acceleration Boundary DesorptionPlasma…

8. April 19 th 2011 8 H. Yasuda. Plasma Polymerization, Academic Press, 1985Plasma… Bicyclic polymerization Plasma excitation

9. April 19 th 2011 9 Power (W) Impulsion length (10 -3 s – 10 -6 s) Substrate Plasma off Vitesse de déposition depositionPlasma… Species density Substrate Plasma on Ions UVElectrons Radicals Molecules modification deposition ablation

10. April 19 th 2011 10 Plasma polymerization setup Schéma simplifié du mécanisme de polymérisation R.F. pulsées 30 min R/R’ = -COOH -CH 2 OR -C=O -CH 3 -OH … Maleic anhydride High reactivity Monomer Pump Liquid nitrogen Fittings Pressure gauge Copper turns O-ring Gas Matching Substrate Glass plate Valve R.F. generator 13,56 MHz box

11. April 19 th 2011 11 Pulsed plasma polymerization Desired plasma coating properties : -Highest concentration of maleic anhydride functionalities incorporated in polymer - Low roughness - Ultra thin plasma polymer coating t off t on Variation of t on t off P p Variation of plasma polymer properties Need to optimize plasma parameters Puissance P p Monitoring RF signal via an oscilloscope

12. April 19 th 2011 12 Use of chemometric tools ParameterLow (-)Center (0)High (+) P p (peak power, W) 105090 t on (µs)20410800 t off (µs)206101200 Domain of variation of plasma parameters for DOE study ParameterLow (-)Center (0)High (+) P p (peak power, W) 51015 t on (µs)132639 t off (µs)120012501300 Domain of variation of refined parameters for central composite design Matrix of experiments Response Experiment P p (W) t on (µs) t off (µs) Anhydride group retention (%) Thickness (nm) Roughness (nm) 1---19,0191,30,44 2+--12,8120,10,39 3-+-12,3114,20,99 4++-0,0 0,06 5--+30,038,70,19 6+-+15,8128,70,21 7-++11,242,00,10 8+++10,387,50,20 900011,1584,90,55 1000011,2589,00,88 1100011,8387,20,61 Area of interest

13. April 19 th 2011 13 Optimized conditions : Optimized conditions : 5W, 25µs on-time, 1200µs off-time XPS IRRAS AFM Anhydride group retention : Anhydride group retention : 32% Film thickness : Film thickness : 15 nm Roughness : Roughness : ~ 0.2 nm AFM image - Phase z=3° - 2μm x 2μm Plasma coating properties Anhydride groups C 1s Elongation cycles anhydride conjugués Conjugated anhydrides – cycle elongation C-O-C elongation C=O antisym. vibration C=O sym. vibration Wavenumber (cm -1 ) Binding energy (eV)

14. April 19 th 2011 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 Surface morphology after plasma coating deposition

15. April 19 th 2011 15 Plasma coating functionalization Aminolysis reaction Functionalization R = Diene or Dienophile Functionalized plasma coating

16. April 19 th 2011 16 Bifunctional molecules Available commercially No commercial availability SYNTHESIS

17. April 19 th 2011 17 Synthesis of the bifunctional diene Targeted molecule : Plasma polymer thin film Au 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. April 19 th 2011 18 Plasma coating functionalization 120°C – 2 hrs under vacuum Gas phase b) c) Plasma coating a) Plasma coating d) Plasma coating Plasma coating functionalized with dienophile groups Wavenumber (cm -1 ) Wettability measurements Nature des échantillons Advancing contact angle Receding contact angle Plasma coating (anhydride groups) 62° ± 2°< 10° Plasma coating functionalized with allylamine - AMIDE 12° ± 2°< 10° Plasma coating functionalized with allylamine - IMIDE 60° ± 2°< 10°

19. April 19 th 2011 19 Diels-Alder reaction Concerted reaction : C C C C CH 2Diene Transition state C C H H H Dienophile Au C H C C C CH 2 C C H H Au C C C C CH 2 C C H H H Newly created C-C bonds Au

20. April 19 th 2011 20 Reaction kinetics of interfacial Diels-Alder Diene used for this study Pulsed plasma polymer CPdSi Si [(triméthylsilyl)methyl]cyclopentadiene

21. April 19 th 2011 21  Following Diels-Alder reaction kinetics 59 64 69 74 79 84 89 0100020003000400050006000 Time (s) Advancing contact angle (°) 294 K308 K 318 K328 K 278 K288 K Wettability measurements:

22. April 19 th 2011 22 Functional group density Plasma polymer Cyclohexane θ alkene = 60° θ bicyclo = 87° θ expérimental Cassie equation : Cos θ experimental =  alkene. Cos θ alkene +  bicyclo. Cos θ bicyclo  alkene  bicyclo

23. April 19 th 2011 23 Following Diels-Alder reaction kinetics XPS measurements – following Si/N ratio Si/N = 1 when all dienophile groups have undergone a Diels-Alder reaction CPS Binding energy (eV) Polymère plasma 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 0100020003000400050006000 Time (s) Si/N ratio (area under peak) 293 K 308 K 328 K

24. April 19 th 2011 24 Interfacial Diels-Alder reaction between solid substrates Substrate 1 aluminum Substrate 2 aluminum or rubber Plasma polymerization Functionalization with diene groups Functionalization with dienophile groups Substrates assembled In a curing press Is the Diels-Alder reaction effective between 2 functionalized substrates

25. April 19 th 2011 25 Disponibility of dienophile groups Imide Amide Dicumyle peroxyde Aluminum Crosslinking reaction Press 170ºC - 40min – 3 MPa Aluminum Aluminium Aluminum 1 st step : verify that dienophile groups immobilized on aluminum are available to react during EPDM peroxide cure EPDM

26. April 19 th 2011 26 Disponibility of dienophile groups 180 degree peel tests Interfacial fracture energy -200 0 200 400 600 800 1000 1200 020406080100120 Peeled length (mm) W 180 (J/m²) Amide Imide (vacuum) Imide (atmosphere) Reference 20 mm/min 5 mm/min 20 mm/min EPDM cohesion energy Dienophile groups seem to be available for interfacial reaction EPDM Aluminum 180 degrees

27. April 19 th 2011 27 Analysis of peeled substrates Wettability measurements Contact angle Aluminum EPDM (after peel test) Advancing: 103º ± 2º Receding : 42º ± 2º Advancing: 100º ± 2º Receding : 35º ± 2° Cohesive fracture located in EPDM Bare EPDM : A: 103º R: 45º 

28. April 19 th 2011 28 Interfacial Diels-Alder reaction between functionalized EPDM / aluminum Substrates assembled in a curing press for different conditions of pressure, time and temperature EPDM 30°C – 70°C 30min – 120 min 0,08 MPa – 0,32 MPa DOE performed to optimize assembling conditions Pulsed plasma polymer

29. April 19 th 2011 29 Interfacial Diels-Alder reaction between functionalized EPDM / aluminum Peeled length (mm) Peel energy between 2 dienophile functionalized substrates Aluminum EPDM Experiment N° Temperature (°C) Time (min.) Pressure (MPa) Peel energy (J.m -2 ) 130 0,0820 270300,08280 3301200,088 4701200,08224 530 0,3232 670300,32248 7301200,32280 8701200,32448 950750,224 1050750,220 1150750,224 Peel energy between 2 substrates respectively functionalized with diene and dienophile groups No interfacial bond formation Interfacial Diels-Alder seem to proceed !

30. April 19 th 2011 30 Interfacial Diels-Alder reaction – AFM images of aluminum substrate before and after peel test EPDM ALUMINIUM Pelage 180° Height image Ra = 62.32 nm Phase image Phase image Height image Ra = 18.74 nm Plasma coated aluminum substrate (prior to peel test) Aluminum substrate after peel test

31. April 19 th 2011 31 Interfacial Diels-Alder reaction – AFM images of EPDM substrate before and after peel test EPDM ALUMINIUM 180° peel test Phase image Phase image Height image Ra = 13.9 nm Plasma coated EPDM (prior to peel test) EPDM substrate after peel test Height image Ra = 60.6 nm Height image Ra = 16.1 nm Phase image Bare EPDM

32. April 19 th 2011 32 Analysis of peeled substrates Wettability measurements  Contact angles Aluminum EPDM (after peel test) Advancing: 100º ± 2º Receding : 40º ± 2º Advancing: 103º ± 2º Receding : 42º ± 2° Cohesive fracture located in EPDM Bare EPDM : A: 103º R: 45º

33. April 19 th 2011 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 Peeled length (mm) Ambient temperature

34. April 19 th 2011 34 Conclusion - perspectives Diels-Alder Retro Diels-Alder 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