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Lorentz - 2008
Atomistic Modelling of Deformed Polymer Glasses
Alexey Lyulin
Group Polymer Physics, Eindhoven Polymer Laboratories and Dutch Polymer
Institute, Technische Universiteit Eindhoven, The Netherlands
Lorentz - 2008
Participants
TU Eindhoven TU Athens MPI-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, Moscow Tver University N.K. Balabaev M.A. Mazo A.S. Pavlov E.F. Olejnik I. Neratova
Lorentz - 2008
Motivation
Brittle
Polystyrene
Polycarbonate
vs.vs. ToughTough
Lorentz - 2008
Another puzzle
Lorentz - 2008
Stress-strain behaviour
Intrinsic microscopic response vs chemical structure unclear(e.g. H.E.H. Meijer et al., TU/e and DPI)
PCPS
extension
PC
PS
compression
Lorentz - 2008
Thermal and mechanical rejuvenation
Thermal: heating up above Tg, then quenching
H.G.H. van Melick, PhD thesis, Eindhoven, 2002
Lorentz - 2008
Thermal and mechanical rejuvenation
H.G.H. van Melick, PhD thesis, Eindhoven, 2002
Mechanical: deformation above the yield point, then compression
Lorentz - 2008
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 !
Lorentz - 2008
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 ?
Lorentz - 2008
T ~ Tg P = 1 atm
Equilibration
PS PC
Lorentz - 2008
Characteristic ratio
PS PC8.2C 1.7C
SANS: Boothroyd et al., 8.7-9.6simulations: Han and Boyd, 10.2
Sun and Faller, 6.5
SANS: Gawrisch, Brereton, Fischer, 1.9-2simulations: Hutnik, Argon, Suter, 1.6
1/ 2(1 )nC C n
(Wittmer, Meyer, Baschnagel, Johner, Obukhov, Mattioni, Müller, Semenov, PRL, 2004)
Lorentz - 2008
Cooling down below Tg
Cooling time, c 10 ps (quenched)
25 ns (annealed)
Lorentz - 2008
Orientational mobility
22( ) 3/ 2( (0) ( )) 1/ 2P t tb bb
polystyrene polycarbonate
Lorentz - 2008
Equilibrated films, T =540 K
8x80, 38 Å
16x80, 65 Å
32x80, 112 Å
Lorentz - 2008
Orientational mobility
film
bulk
Lorentz - 2008
P2 relaxation-time distribution (CONTIN analysis)
( ) (ln )exp( / ) lnACF t F t d
AVL, M.A.J. Michels, J. Non-Cryst. Solids 2006
-process
-process
PC
Lorentz - 2008
Temperature dependence of P2 relaxation times
polystyrene polycarbonate
~ 50 ps ~ 500 ps<<T = 300K
Lorentz - 2008
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
1000y ps 0.005 Å/ps
Lorentz - 2008
PC:
T << Tg
PS:
Lorentz - 2008
Simulation vs. experiment
PC
PS
H.G.H. van Melick et al., Polymer 2003AVL, B. Vorselaars, M. Mazo, N. Balabaev, M.A.J. Michels, Europhys. Lett. 2005
Lorentz - 2008
Simulation vs. experiment
quenched
annealed
polystyrene
AVL, M.A.J. Michels, Phys. Rev. Lett., 2007H.G.H. van Melick, PhD thesis, Eindhoven, 2002
polystyrene
Lorentz - 2008
Three time scales
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
for both polymers
~
Lorentz - 2008
Stretching - compression loop: quenched samples
mechanical overaging because of the process
- faster for PS, slower for PC- effect is larger for PC
Lorentz - 2008
Stretching - compression loop: annealed samples
Lorentz - 2008
Energy partitioning
AVL, M.A.J. Michels, Phys. Rev. Lett., 2007
En
erg
y d
istrib
utio
n
mechanically rejuvenated glass is different from thermally rejuvenated glass
Lorentz - 2008
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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