Stress-optical behaviour near the Tg and melt flow-induced anisotropy in amorphous polymers

Müller, René; Pesce, Jean-Jacques

doi:10.1016/0032-3861(94)90870-2

Cited by 43 publications

(67 citation statements)

References 8 publications

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“…If the electric polarization tensor of a bead is uniaxial along the bond direction, the deviatoric part of the dielectric tensor is proportional to that of the tensor Q αβ in (3.13). In accord with the experiment, 16 our data collapse onto a universal curve independent of T both in the linear (Q xy 0.05) and nonlinear (Q xy 0.05) regimes.…”

Section: Steady State Behavior In Shear Flowsupporting

confidence: 87%

“…If measurements are made in steady states, it holds even close to T g . 16 For its validity, we need to require that the form contribution to ǫ αβ is negligible as compared to the intrinsic contribution 15 and that the glassy part of the stress is negligible as compared to the usual entropic part. Thus it is violated when the form part is relevant such as in polymer solutions close to the demixing critical point or when measurements are made in transient states close to T g .…”

Section: G(t) = G G (T) + G R (T) (12)mentioning

confidence: 99%

“…More pronounced overshoot was already reported at high shear in MD simulation of much longer unentangled alkane chains (C 100 H 202 ). 12 In experiments, [16][17][18][19] the stress-optical relation is transiently violated at low T after application of elongational flow due to the enhancement of the glassy component of the stress. For shear flow, Fig.10 displays our MD results at T = 0.2 after application of shear at t = 0 in a stress-optical diagram, where the solid lines are the averages over ten independent runs.…”

Section: Transient Viscoelastic Behaviormentioning

confidence: 99%

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Dynamics and rheology of a supercooled polymer melt in shear flow

Yamamoto

Ōnuki

2002

The Journal of Chemical Physics

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Using molecular dynamics simulations, we study dynamics of a model polymer melt composed of short chains with bead number N = 10 in supercooled states. In quiescent conditions, the stress relaxation function G(t) is calculated, which exhibits a stretched exponential relaxation on the time scale of the α relaxation time τα and ultimately follows the Rouse dynamics characterized by the time τR ∼ N 2 τα. After application of shearγ, transient stress growth σxy(t)/γ first obeys the linear growth t 0 dt ′ G(t ′ ) for strain less than 0.1 but saturates into a non-Newtonian viscosity for larger strain. In steady states, shear-thinning and elongation of chains into ellipsoidal shapes take place for shearγ larger than τ −1 R . In such strong shear, we find that the chains undergo random tumbling motion taking stretched and compact shapes alternatively. We examine the validity of the stressoptical relation between the anisotropic parts of the stress tensor and the dielectric tensor, which are violated in transient states due to the presence of a large glassy component of the stress. We furthermore introduce time-correlation functions in shear to calculate the shear-dependent relaxation times, τα(T,γ) and τR(T,γ), which decrease nonlinearly as functions ofγ in the shear-thinning regime.

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Section: Steady State Behavior In Shear Flowsupporting

confidence: 87%

Section: G(t) = G G (T) + G R (T) (12)mentioning

confidence: 99%

Section: Transient Viscoelastic Behaviormentioning

confidence: 99%

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Dynamics and rheology of a supercooled polymer melt in shear flow

Yamamoto

Ōnuki

2002

The Journal of Chemical Physics

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“…Such hierarchical relaxation behavior arises from rearrangements of jammed atomic configurations and subsequent evolution of chain conformations described by the Rouse or reptation dynamics [3,4]. The stress-optical relation between birefringence and stress has also been reported to be violated as the temperature T is approached the glass transition temperature T g [5][6][7], obviously owing to enhancement of a glassy part of the stress.Recent simulations on glassy polymer melts have mainly treated self-motions of particles in quiescent states [8][9][10]. However, not enough theoretical efforts have been made on the rheological properties of glassy polymers.…”

mentioning

confidence: 99%

mentioning

confidence: 99%

Dynamics and rheology of a supercooled polymer melt

Yamamoto

Ōnuki

2000

AIP Conference Proceedings

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Molecular dynamics simulations are performed for a polymer melt composed of short chains in quiescent and sheared conditions. The stress relaxation function G(t) exhibits a stretched exponential form in a relatively early stage and ultimately follows the Rouse function in quiescent supercooled state. Transient stress evolution after application of shear obeys the linear growth t 0 dt ′ G(t ′ ) for strain less than 0.1 and then saturates into a non-Newtonian viscosity. In steady states, strong shear-thinning and elongation of chains into ellipsoidal shapes are found at extremely small shear. A glassy component of the stress is much enhanced in these examples.PACS numbers: 83.10. Nn, 83.20.Jp, 83.50.By, 64.70.Pf Stress and dielectric relaxations of glassy polymer melts occur from microscopic to macroscopic time scales in very complicated manners [1,2]. Experiments have shown that the stress relaxation function G(t) exhibits a glassy stretched exponential decay, a glass-rubber transition, a rubbery plateau, and a terminal decay, in this order over many decades of time. Such hierarchical relaxation behavior arises from rearrangements of jammed atomic configurations and subsequent evolution of chain conformations described by the Rouse or reptation dynamics [3,4]. The stress-optical relation between birefringence and stress has also been reported to be violated as the temperature T is approached the glass transition temperature T g [5][6][7], obviously owing to enhancement of a glassy part of the stress.Recent simulations on glassy polymer melts have mainly treated self-motions of particles in quiescent states [8][9][10]. However, not enough theoretical efforts have been made on the rheological properties of glassy polymers. Hence, we will first study linear rheology of a model short chain system via very long molecular dynamics simulations. Then, we will demonstrate that chains are very easily elongated at extremely small shear rateγ on the order of the inverse Rouse time. In our model all the bead particles interact with a Lennard-Jones potential of the form [4,8,10], U LJ (r) = 4ǫ[(σ/r) 12 − (σ/r) 6 ] + ǫ. It is cut off at the minimum distance 2 1/6 σ, so we use its repulsive part only to prevent spatial overlap of particles. Consecutive beads on each chain are connected by an anharmonic spring of the form, U F (r) = − 1 2 k c R 2 0 ln[1 − (r/R 0 ) 2 ] with k c = 30ǫ/σ 2 and R 0 = 1.5σ, so the bond length cannot exceed R 0 . In a cubic box with length L = 10σ under the periodic boundary condition, we put M = 100 chains composed of N = 10 beads. The number density is fixed at a very high value of n = N M/V = 1/σ 3 , which results in severely jammed configurations at low T . We will measure space and time in units of σ and τ 0 = (mσ 2 /ǫ) 1/2 with m being the mass of a bead. The temperature T will be measured in units of ǫ/k B . Simulations were performed in normal (T = 1.0) and supercooled (T = 0.4 and 0.2) states with and without shear. The bond lengths b j = |R j − R j+1 | between consecutive beads on each cha...

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“Anomalous” Phenomena

2017

Nonlinear Polymer Rheology

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Stress-optical behaviour near the Tg and melt flow-induced anisotropy in amorphous polymers

Cited by 43 publications

References 8 publications

Dynamics and rheology of a supercooled polymer melt in shear flow

Dynamics and rheology of a supercooled polymer melt in shear flow

Dynamics and rheology of a supercooled polymer melt

“Anomalous” Phenomena

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