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

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Lorentz Participants TU EindhovenTU AthensMPI-P Mainz Thijs MichelsDoros TheodorouNico v.d. Vegt B. Vorselaars C. TzoumanekasV. Harmandaris T. Mulder L. Peristeras E. de Caluwe H.E.H. Meijer L. Govaert IMPB RAN, PuschinoICP RAN, MoscowTver University N.K. BalabaevM.A. MazoA.S. Pavlov E.F. OlejnikI. Neratova

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Lorentz Motivation Brittle Polystyrene Polycarbonate vs. Tough

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Lorentz Another puzzle

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

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Lorentz Thermal and mechanical rejuvenation Thermal: heating up above T g, then quenching H.G.H. van Melick, PhD thesis, Eindhoven, 2002

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

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Lorentz Thermal and mechanical rejuvenation Thermal: heating up above T g, then quenching Mechanical: deformation above the yield point, then compression Bulk mechanics similar Microscopically the same ???? No !

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Lorentz 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 ?

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Lorentz T ~ T g P = 1 atm Equilibration PS PC

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

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Lorentz Cooling down below T g Cooling time, c 10 ps (quenched) 25 ns (annealed)

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Lorentz Orientational mobility b polystyrenepolycarbonate

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

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Lorentz Orientational mobility film bulk

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Lorentz P 2 relaxation-time distribution (CONTIN analysis) AVL, M.A.J. Michels, J. Non-Cryst. Solids 2006 -process -process PC

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Lorentz Temperature dependence of P 2 relaxation times polystyrene polycarbonate ~ 50 ps ~ 500 ps << T = 300K

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Lorentz 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 =0 L =65% L =110% AVL, N.K. Balabaev, M.A. Mazo, M.A.J. Michels, Macromolecules 2004 Å/ps

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Lorentz PC: T << T g PS:

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

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

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

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

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Lorentz Stretching - compression loop: annealed samples

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

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Lorentz Summary, questions T g, 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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