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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


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


Polystyrene

Polycarbonate

Motivation

Brittle

vs. Tough


Another puzzle


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)


Thermal and mechanical rejuvenation

  • Thermal: heating up above Tg,then quenching

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


Thermal and mechanical rejuvenation

  • Mechanical: deformation above the yield point, then compression

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


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

  • 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 ?


Equilibration

T ~ TgP = 1 atm

PS

PC


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)


Cooling down below Tg

  • Cooling time, c

10 ps (quenched)

25 ns (annealed)


b

Orientational mobility

polystyrene

polycarbonate


Equilibrated films, T =540 K

8x80, 38 Å

32x80, 112 Å

16x80, 65 Å


Orientational mobility

film

bulk


P2 relaxation-time distribution (CONTIN analysis)

-process

-process

PC

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


Temperature dependence of P2 relaxation times

polycarbonate

polystyrene

T = 300K

 ~ 500 ps

~ 50 ps

<<


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


PS:

T << Tg

PC:


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


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


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


Stretching - compression loop: quenched samples

  • mechanical overaging because of the  process

  • faster for PS, slower for PC

  • effect is larger for PC


Stretching - compression loop: annealed samples


Energy partitioning

  • mechanically rejuvenated glass is different from thermally rejuvenated glass

Energy distribution

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


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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