Competition of time and spatial scales in polymer glassy dynamics: Rejuvenation and confinements effects

A.V. Lyulin, D. Hudzinskyy, E. Janiaud, A. Chateauminois

Research output: Contribution to journalArticleAcademicpeer-review

11 Citations (Scopus)

Abstract

We use molecular-dynamics (MD) simulations and an original lateral contact experiment to explore the influence of mechanical history on polymer mechanical behavior and segmental mobility. Two typical glassy polymers are considered: bulk acrylate (experiments) and atactic polystyrene (aPS) in a bulk and in thin films (simulations). Stress-strain behavior has been investigated both experimentally for sheared, 50 µm thick, acrylate films and by MD simulations of an aPS in a bulk for two different strain rates in a closed extension–recompression loops. Cyclic shear strains applied in the plastic regime were found experimentally to induce a progressive transition of the mechanical response of the polymer glass toward a steady state which is characterized by a strong reduction of the apparent – non linear – shear modulus. The dynamics of the polymer glass in this yielded state was subsequently analyzed from a measurement of the time dependent linear viscoelastic properties at various imposed frequencies. Immediately after the cyclic plastic deformation, mechanical "rejuvenation" of the polymer is evidenced by a drop in the storage modulus and an increase in the loss modulus, as compared to the initial values recorded before plastic deformation. A progressive recovery of the viscoelastic properties is also measured as a function of time as a result of the enhanced aging rate of the system. This experimentally observed mechanical rejuvenation of polymer has been for the first time connected to the drastic increase in the simulated segmental mobility. A simulated distribution of relaxation times shows a shift to shorter times of the a and ß relaxation processes which is consistent with the observed experimental changes in the viscoelastic modulus after rejuvenation. Finally, we present our first findings on the thickness- and substrate-dependence of the simulated glass transition temperature for thin aPS films. We observe the decrease of the glass transition temperature with film thickness, but for extremely thin (less than 2 nm) films.
Original languageEnglish
Pages (from-to)567-574
JournalJournal of Non-Crystalline Solids
Volume357
DOIs
Publication statusPublished - 2011

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Polymers
Polystyrenes
polymers
polystyrene
acrylates
glass transition temperature
plastic deformation
Molecular dynamics
Plastic deformation
Elastic moduli
molecular dynamics
Glass
simulation
glass
shear strain
Shear strain
Computer simulation
Relaxation processes
Thick films
Relaxation time

Cite this

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title = "Competition of time and spatial scales in polymer glassy dynamics: Rejuvenation and confinements effects",
abstract = "We use molecular-dynamics (MD) simulations and an original lateral contact experiment to explore the influence of mechanical history on polymer mechanical behavior and segmental mobility. Two typical glassy polymers are considered: bulk acrylate (experiments) and atactic polystyrene (aPS) in a bulk and in thin films (simulations). Stress-strain behavior has been investigated both experimentally for sheared, 50 µm thick, acrylate films and by MD simulations of an aPS in a bulk for two different strain rates in a closed extension–recompression loops. Cyclic shear strains applied in the plastic regime were found experimentally to induce a progressive transition of the mechanical response of the polymer glass toward a steady state which is characterized by a strong reduction of the apparent – non linear – shear modulus. The dynamics of the polymer glass in this yielded state was subsequently analyzed from a measurement of the time dependent linear viscoelastic properties at various imposed frequencies. Immediately after the cyclic plastic deformation, mechanical {"}rejuvenation{"} of the polymer is evidenced by a drop in the storage modulus and an increase in the loss modulus, as compared to the initial values recorded before plastic deformation. A progressive recovery of the viscoelastic properties is also measured as a function of time as a result of the enhanced aging rate of the system. This experimentally observed mechanical rejuvenation of polymer has been for the first time connected to the drastic increase in the simulated segmental mobility. A simulated distribution of relaxation times shows a shift to shorter times of the a and {\ss} relaxation processes which is consistent with the observed experimental changes in the viscoelastic modulus after rejuvenation. Finally, we present our first findings on the thickness- and substrate-dependence of the simulated glass transition temperature for thin aPS films. We observe the decrease of the glass transition temperature with film thickness, but for extremely thin (less than 2 nm) films.",
author = "A.V. Lyulin and D. Hudzinskyy and E. Janiaud and A. Chateauminois",
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doi = "10.1016/j.jnoncrysol.2010.08.008",
language = "English",
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journal = "Journal of Non-Crystalline Solids",
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Competition of time and spatial scales in polymer glassy dynamics: Rejuvenation and confinements effects. / Lyulin, A.V.; Hudzinskyy, D.; Janiaud, E.; Chateauminois, A.

In: Journal of Non-Crystalline Solids, Vol. 357, 2011, p. 567-574.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Competition of time and spatial scales in polymer glassy dynamics: Rejuvenation and confinements effects

AU - Lyulin, A.V.

AU - Hudzinskyy, D.

AU - Janiaud, E.

AU - Chateauminois, A.

PY - 2011

Y1 - 2011

N2 - We use molecular-dynamics (MD) simulations and an original lateral contact experiment to explore the influence of mechanical history on polymer mechanical behavior and segmental mobility. Two typical glassy polymers are considered: bulk acrylate (experiments) and atactic polystyrene (aPS) in a bulk and in thin films (simulations). Stress-strain behavior has been investigated both experimentally for sheared, 50 µm thick, acrylate films and by MD simulations of an aPS in a bulk for two different strain rates in a closed extension–recompression loops. Cyclic shear strains applied in the plastic regime were found experimentally to induce a progressive transition of the mechanical response of the polymer glass toward a steady state which is characterized by a strong reduction of the apparent – non linear – shear modulus. The dynamics of the polymer glass in this yielded state was subsequently analyzed from a measurement of the time dependent linear viscoelastic properties at various imposed frequencies. Immediately after the cyclic plastic deformation, mechanical "rejuvenation" of the polymer is evidenced by a drop in the storage modulus and an increase in the loss modulus, as compared to the initial values recorded before plastic deformation. A progressive recovery of the viscoelastic properties is also measured as a function of time as a result of the enhanced aging rate of the system. This experimentally observed mechanical rejuvenation of polymer has been for the first time connected to the drastic increase in the simulated segmental mobility. A simulated distribution of relaxation times shows a shift to shorter times of the a and ß relaxation processes which is consistent with the observed experimental changes in the viscoelastic modulus after rejuvenation. Finally, we present our first findings on the thickness- and substrate-dependence of the simulated glass transition temperature for thin aPS films. We observe the decrease of the glass transition temperature with film thickness, but for extremely thin (less than 2 nm) films.

AB - We use molecular-dynamics (MD) simulations and an original lateral contact experiment to explore the influence of mechanical history on polymer mechanical behavior and segmental mobility. Two typical glassy polymers are considered: bulk acrylate (experiments) and atactic polystyrene (aPS) in a bulk and in thin films (simulations). Stress-strain behavior has been investigated both experimentally for sheared, 50 µm thick, acrylate films and by MD simulations of an aPS in a bulk for two different strain rates in a closed extension–recompression loops. Cyclic shear strains applied in the plastic regime were found experimentally to induce a progressive transition of the mechanical response of the polymer glass toward a steady state which is characterized by a strong reduction of the apparent – non linear – shear modulus. The dynamics of the polymer glass in this yielded state was subsequently analyzed from a measurement of the time dependent linear viscoelastic properties at various imposed frequencies. Immediately after the cyclic plastic deformation, mechanical "rejuvenation" of the polymer is evidenced by a drop in the storage modulus and an increase in the loss modulus, as compared to the initial values recorded before plastic deformation. A progressive recovery of the viscoelastic properties is also measured as a function of time as a result of the enhanced aging rate of the system. This experimentally observed mechanical rejuvenation of polymer has been for the first time connected to the drastic increase in the simulated segmental mobility. A simulated distribution of relaxation times shows a shift to shorter times of the a and ß relaxation processes which is consistent with the observed experimental changes in the viscoelastic modulus after rejuvenation. Finally, we present our first findings on the thickness- and substrate-dependence of the simulated glass transition temperature for thin aPS films. We observe the decrease of the glass transition temperature with film thickness, but for extremely thin (less than 2 nm) films.

U2 - 10.1016/j.jnoncrysol.2010.08.008

DO - 10.1016/j.jnoncrysol.2010.08.008

M3 - Article

VL - 357

SP - 567

EP - 574

JO - Journal of Non-Crystalline Solids

JF - Journal of Non-Crystalline Solids

SN - 0022-3093

ER -