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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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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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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


Motivation l.jpg

Polystyrene

Polycarbonate

Motivation

Brittle

vs. Tough


Another puzzle l.jpg

Another puzzle


Stress strain behaviour l.jpg

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)


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Thermal and mechanical rejuvenation

  • Thermal: heating up above Tg,then quenching

H.G.H. van Melick, PhD thesis, Eindhoven, 2002


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Thermal and mechanical rejuvenation

  • Mechanical: deformation above the yield point, then compression

H.G.H. van Melick, PhD thesis, Eindhoven, 2002


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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 !


Ps vs pc as model amorphous polymers l.jpg

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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Equilibration

T ~ TgP = 1 atm

PS

PC


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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)


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Cooling down below Tg

  • Cooling time, c

10 ps (quenched)

25 ns (annealed)


Orientational mobility l.jpg

b

Orientational mobility

polystyrene

polycarbonate


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Equilibrated films, T =540 K

8x80, 38 Å

32x80, 112 Å

16x80, 65 Å


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Orientational mobility

film

bulk


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P2 relaxation-time distribution (CONTIN analysis)

-process

-process

PC

AVL, M.A.J. Michels, J. Non-Cryst. Solids2006


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Temperature dependence of P2 relaxation times

polycarbonate

polystyrene

T = 300K

 ~ 500 ps

~ 50 ps

<<


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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


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PS:

T << Tg

PC:


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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


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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


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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


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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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Stretching - compression loop: annealed samples


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Energy partitioning

  • mechanically rejuvenated glass is different from thermally rejuvenated glass

Energy distribution

AVL, M.A.J. Michels, Phys. Rev. Lett., 2007


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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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