Dynamics and rheology of a supercooled polymer melt in shear flow

Yamamoto, Ryōichi; Ōnuki, Akira

doi:10.1063/1.1488589

Cited by 41 publications

(51 citation statements)

References 44 publications

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“…With this density and temperature, the configuration of bead particles becomes severely jammed, resulting in the complicated nonNewtonian viscosity and long-time relaxation phenomena typically seen in glassy polymers. [44][45][46] We assume that the macroscopic quantities are uniform in the x-and z-directions, @=@x ¼ @=@z ¼ 0. The macroscopic velocity v is described by the following equations: …”

Section: Multiscale Modelling and The Simulation Methodsmentioning

confidence: 99%

Multiscale Modeling for Polymeric Flow: Particle-Fluid Bridging Scale Methods

et al. 2013

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Multiscale simulation methods have been developed based on the local stress sampling strategy and applied to three flow problems with different difficulty levels: (a) general flow problems of simple fluids, (b) parallel (one-dimensional) flow problems of polymeric liquids, and (c) general (two-or three-dimensional) flow problems of polymeric liquids. In our multiscale methods, the local stress of each fluid element is calculated directly by performing microscopic or mesoscopic simulations according to the local flow quantities instead of using any constitutive relations. For simple fluids (a), such as the Lenard-Jones liquid, a multiscale method combining molecular dynamics (MD) and computational fluid dynamics (CFD) simulations is developed rather straightforwardly based on the local stationarity assumption without memories of the flow history. For polymeric liquids in parallel flows (b), the multiscale method is extended to take into account the memory effects that arise in hydrodynamic stress due to the slow relaxation of polymer-chain conformations. The memory of polymer dynamics on each fluid element is thus resolved by performing MD simulations in which cells are fixed at the mesh nodes of the CFD simulations. The complicated viscoelastic flow behaviors of a polymeric liquid confined between oscillating plates are simulated using the multiscale method. For general (two-or three-dimensional) flow problems of polymeric liquids (c), it is necessary to trace the history of microscopic information such as polymer-chain conformation, which carries the memories of past flow history, along the streamline of each fluid element. A Lagrangian-based CFD is thus implemented to correctly advect the polymerchain conformation consistently with the flow. On each fluid element, coarse-grained polymer simulations are carried out to consider the dynamics of entangled polymer chains that show extremely slow relaxation compared to microscopic time scales. This method is successfully applied to simulate a flow around a cylindrical obstacle.

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Section: Multiscale Modelling and The Simulation Methodsmentioning

confidence: 99%

Multiscale Modeling for Polymeric Flow: Particle-Fluid Bridging Scale Methods

et al. 2013

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“…Hence such forces might responsible of the nearly-ballistic dependence of the relaxation time on the wave-vector and of CE decay of time correlators with an exponent ∼ 1.5 [3,4,5]. Similarly, if the system is sheared and the perturbation gives (at least locally) rise to a linear displacement in time one can again expect this type of relaxation [4,19]. Interestingly, in the non-ergodic gels just mentioned the relaxation is supposed to occur via the motion of the connecting branches of the gel network and formation or breaking of network nodes, see Ref.…”

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confidence: 98%

Length-Scale-Dependent Relaxation in Colloidal Gels

Gado¹,

Kob

2007

Phys. Rev. Lett.

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We use molecular dynamics computer simulations to investigate the relaxation dynamics of a simple model for a colloidal gel at a low volume fraction. We find that due to the presence of the open spanning network this dynamics shows at low temperature a non-trivial dependence on the wave-vector which is very different from the one observed in dense glass-forming liquids. At high wave vectors the relaxation is due to the fast cooperative motion of the branches of the gel network, whereas at low wave vectors the overall rearrangements of the heterogeneous structure produce the relaxation process.PACS numbers: 82.70. Gg, 82.70.Dd, 64.70.Pf, 67.40.Fd In gels, the deep connection existing between their unusual dynamics and the open network characterizing their structure is still not understood [1,2]. In the dramatic slowing down of the dynamics accompanying the gel formation, the relaxation functions are often stretched and/or, most remarkably, compressed, i.e. the time correlators decay faster than an exponential [3,4,5,6,7], showing a complex dependence on length scale. These findings suggest that different relaxation mechanisms interplay at a microscopic level, which have not been elucidated yet [8,9]. In the present paper, we show that the formation of the gel network does induce a nontrivial length scale dependence of the dynamics in a simple model for colloidal gels. We use molecular dynamics computer simulations to study the gel formation from the equilibrium sol phase. Our results give evidence that in the incipient gel, the relaxation at high wave vectors is due to the fast cooperative motion of pieces of the gel structure, whereas at low wave vectors the overall rearrangements of the heterogeneous gel make the system relax via a stretched exponential decay of the time correlators. The coexistence of such diverse relaxation mechanisms is determined by the formation of the gel network (i.e. the onset of the elastic response of the system) and it is characterized by a typical crossover length which is of the order of the network mesh size. This is the first work where such a characterization of the gel dynamics in colloidal systems has been achieved, thus making important progress as compared to previous numerical studies [9,10,11,12].In colloidal suspensions at low volume fractions gelation competes and/or interplays with phase separation. As a consequence, coarsening or ordering processes due to the underlying thermodynamics often interfere with the gel dynamics. Whereas in the experiments the time scale typical of the micro or macro-phase separation is often much longer than the observation time scales [3,4], this is not the case in numerical studies using traditional models for colloidal suspensions, where the investigation of the gel dynamics has been until now severely hindered [8,9,10,11]. In order to overcome this problem, we have developed a model in which directional interactions are able to produce a persistent gel network at relatively high temperatures, where phase separation does not occur. The...

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“…The competition between the thickening, produced by the aging, and the thinning, induced by shear flow, gives rise to interesting phenomena. On the theoretical and numerical side, evidences of the competition between these two effects come from the extension of slow dynamics theories in complex systems, such as mode coupling theory (MCT) [3], mean-field models [4], trap models [1] and molecular dynamics simulations [5,6,7], to the presence of external driving forces. These studies show that the structural dynamics are very sensitive to even moderate shear rates, providing that the characteristic timescale for structural rearrangements becomes of the same order of the inverse shear rate.…”

Section: Introductionmentioning

confidence: 99%

Aging after shear rejuvenation in a soft glassy colloidal suspension: Evidence for two different regimes

2007

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The aging dynamics after shear rejuvenation in a glassy, charged clay suspension have been investigated through dynamic light scattering (DLS). Two different aging regimes are observed: one is attained if the sample is rejuvenated before its gelation and one after the rejuvenation of the gelled sample. In the first regime, the application of shear fully rejuvenates the sample, as the system dynamics soon after shear cessation follow the same aging evolution characteristic of normal aging. In the second regime, aging proceeds very fast after shear rejuvenation, and classical DLS cannot be used. An original protocol to measure an ensemble averaged intensity correlation function is proposed and its consistency with classical DLS is verified. The fast aging dynamics of rejuvenated gelled samples exhibit a power law dependence of the slow relaxation time on the waiting time.

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Dynamics and rheology of a supercooled polymer melt in shear flow

Cited by 41 publications

References 44 publications

Multiscale Modeling for Polymeric Flow: Particle-Fluid Bridging Scale Methods

Multiscale Modeling for Polymeric Flow: Particle-Fluid Bridging Scale Methods

Length-Scale-Dependent Relaxation in Colloidal Gels

Aging after shear rejuvenation in a soft glassy colloidal suspension: Evidence for two different regimes

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