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Atomistic Modelling of Deformed Polymer Glasses

Atomistic Modelling of Deformed Polymer Glasses. Alexey Lyulin Group Polymer Physics, Eindhoven Polymer Laboratories and Dutch Polymer Institute, Technische Universiteit Eindhoven, The Netherlands. Participants. TU Eindhoven TU Athens MPI-P Mainz

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Atomistic Modelling of Deformed Polymer Glasses

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  1. Atomistic Modelling of Deformed Polymer Glasses Alexey Lyulin Group Polymer Physics, Eindhoven Polymer Laboratories and Dutch Polymer Institute, Technische Universiteit Eindhoven, The Netherlands

  2. Participants TU EindhovenTU AthensMPI-P Mainz • Thijs Michels Doros Theodorou Nico v.d. Vegt • B. Vorselaars C. Tzoumanekas V. Harmandaris • T. Mulder L. Peristeras • E. de Caluwe • H.E.H. Meijer • L. Govaert IMPB RAN, PuschinoICP RAN, MoscowTver University • N.K. Balabaev M.A. Mazo A.S. Pavlov • E.F. Olejnik I. Neratova

  3. Polystyrene Polycarbonate Motivation Brittle vs. Tough

  4. Another puzzle

  5. PS PC PS extension compression PC Stress-strain behaviour • Intrinsic microscopic response vs chemical structure unclear (e.g. H.E.H. Meijer et al., TU/e and DPI)

  6. Thermal and mechanical rejuvenation • Thermal: heating up above Tg,then quenching H.G.H. van Melick, PhD thesis, Eindhoven, 2002

  7. Thermal and mechanical rejuvenation • Mechanical: deformation above the yield point, then compression H.G.H. van Melick, PhD thesis, Eindhoven, 2002

  8. Thermal and mechanical rejuvenation • Thermal: heating up above Tg,then quenching • Mechanical: deformation above the yield point, then compression Bulk mechanics similar Microscopically the same ???? No !

  9. PS vs PC as model amorphous polymers • PS fails brittle, PC tough • PS shows more post-yield stress drop, large strain softening • What is the relation with molecular structure and chain dynamics ?

  10. Equilibration T ~ Tg P = 1 atm PS PC

  11. Characteristic ratio PS PC SANS: Gawrisch, Brereton, Fischer, 1.9-2 simulations: Hutnik, Argon, Suter, 1.6 SANS: Boothroyd et al., 8.7-9.6 simulations: Han and Boyd, 10.2 Sun and Faller, 6.5 (Wittmer, Meyer, Baschnagel, Johner, Obukhov, Mattioni, Müller, Semenov, PRL, 2004)

  12. Cooling down below Tg • Cooling time, c 10 ps (quenched) 25 ns (annealed)

  13. b Orientational mobility polystyrene polycarbonate

  14. Equilibrated films, T =540 K 8x80, 38 Å 32x80, 112 Å 16x80, 65 Å

  15. Orientational mobility film bulk

  16. P2 relaxation-time distribution (CONTIN analysis) -process -process PC AVL, M.A.J. Michels, J. Non-Cryst. Solids2006

  17. Temperature dependence of P2 relaxation times polycarbonate polystyrene T = 300K  ~ 500 ps ~ 50 ps <<

  18. Å/ps Uniaxial extension • PS: 4 chains x N=160, 8 chains x N=80 • PC: 64 chains x N=10, 8 chains x N=80 L=110% L=65% L=0 AVL, N.K. Balabaev, M.A. Mazo, M.A.J. Michels, Macromolecules 2004

  19. PS: T << Tg PC:

  20. PS PC Simulation vs. experiment AVL, B. Vorselaars, M. Mazo, N. Balabaev, M.A.J. Michels, Europhys. Lett.2005 H.G.H. van Melick et al., Polymer 2003

  21. annealed quenched polystyrene polystyrene Simulation vs. experiment H.G.H. van Melick, PhD thesis, Eindhoven, 2002 AVL, M.A.J. Michels, Phys. Rev. Lett., 2007

  22. Three time scales for both polymers • cooling: c ~ 10 ps (quenched) << 25000 ps (annealed) • deformation: y ~ 1000 ps •  - relaxation:  ~ 50 ps (PS) << 500 ps (PC)  (PS) c (quenched) (PC) >> c (quenched) c (annealed) >> ,y

  23. Stretching - compression loop: quenched samples • mechanical overaging because of the  process • faster for PS, slower for PC • effect is larger for PC

  24. Stretching - compression loop: annealed samples

  25. Energy partitioning • mechanically rejuvenated glass is different from thermally rejuvenated glass Energy distribution AVL, M.A.J. Michels, Phys. Rev. Lett., 2007

  26. Summary, questions • Tg, overaging and rejuvenation for typical polymer glasses have been simulated; • Key factors are ratios between three time scales: -  relaxation; - cooling time; - deformation time; • Fast  relaxation for PS, slow for PC; • Thermal and mechanical rejuvenation are microscopically different • Direct measurement of segmental mobility under mechanical deformation

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