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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 Eindhoven TU Athens MPI-P Mainz

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slide1
Atomistic Modelling of Deformed Polymer Glasses

Alexey Lyulin

Group Polymer Physics,

Eindhoven Polymer Laboratories and Dutch Polymer Institute,

Technische Universiteit Eindhoven, The Netherlands

participants
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
motivation
Polystyrene

Polycarbonate

Motivation

Brittle

vs. Tough

stress strain behaviour
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 and mechanical rejuvenation
  • Thermal: heating up above Tg,then quenching

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

thermal and mechanical rejuvenation7
Thermal and mechanical rejuvenation
  • Mechanical: deformation above the yield point, then compression

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

thermal and mechanical rejuvenation8
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 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 ?
slide10
Equilibration

T ~ Tg P = 1 atm

PS

PC

characteristic ratio
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 t g
Cooling down below Tg
  • Cooling time, c

10 ps (quenched)

25 ns (annealed)

orientational mobility
bOrientational mobility

polystyrene

polycarbonate

equilibrated films t 540 k
Equilibrated films, T =540 K

8x80, 38 Å

32x80, 112 Å

16x80, 65 Å

p 2 relaxation time distribution contin analysis
P2 relaxation-time distribution (CONTIN analysis)

-process

-process

PC

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

slide17
Temperature dependence of P2 relaxation times

polycarbonate

polystyrene

T = 300K

 ~ 500 ps

~ 50 ps

<<

uniaxial extension
Å/psUniaxial 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

slide19
PS:

T << Tg

PC:

simulation vs experiment
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

simulation vs experiment21
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
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
Stretching - compression loop: quenched samples
  • mechanical overaging because of the  process
  • faster for PS, slower for PC
  • effect is larger for PC
energy partitioning
Energy partitioning
  • mechanically rejuvenated glass is different from thermally rejuvenated glass

Energy distribution

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

summary questions
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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