Dynamic asymmetry

The above mechanism of the failure of the superposition has also been noted for the entangled PI/PVE blends having just a moderate dynamic asymmetry of the components (cf. Figure 3.13). However, Figure 3.17 demonstrates that the superposition fails for the viscoelastic data of the P199/ PtBS348 blend not only at high co but also at low co. The failure at low co... 

For the global dynamics governing the rubbery/terminal relaxation, the thermorheological complexity of the components is one of the most prominent features. In PI/PVE blends associated with just a moderate dynamic asymmetry of the components, respective components exhibit very minor complexity and behave similarly to the components in chemically uniform blends such as PI/PI blends, as revealed from rheo-optical and dielectric studies. (PI chains have the type-A dipole so that their global motion is dielectrically detected.) The entanglement relaxation in the PI/PVE blends appears to occur through the mechanisms known for the chemically uniform blends, for example, through the reptation and constraint release (CR)/ dynamic tube dilation (DTD) mechanisms. 

Yu et al. (2011) studied rheology and phase separation of polymer blends with weak dynamic asymmetry ((poly(Me methacrylate)/poly(styrene-co-maleic anhydride)). They showed that the failure of methods, such as the time-temperature superposition principle in isothermal experiments or the deviation of the storage modulus from the apparent extrapolation of modulus in the miscible regime in non-isothermal tests, to predict the binodal temperature is not always applicable in systems with weak dynamic asymmetry. Therefore, they proposed a rheological model, which is an integration of the double reptation model and the selfconcentration model to describe the linear viscoelasticity of miscible blends. Then, the deviatirMi of experimental data from the model predictions for miscible... 

Besides the dynamic heterogeneity discussed above, binary miscible polymer blends can be considered as dynamically asymmetric if the two components have a large difference in the glass transition temperatures. Usually the dynamic asymmetry is defined by A = where x " is the relaxation time of the... 

The phases coherence which accompanies any wave scattering, doubled by the correlation of the dynamic localization, leads in corpuscular understanding of the photonic asymmetric transfer. Therefore, the dynamic asymmetry corresponds to the dynamic anomaly in the absorption language, having its bases in the dynamic localization. 

Abstract Phase separation in isotropic condensed matter has so far been believed to be classified into solid and fluid models. When there is a large difference in the characteristic rheological time between the components of a mixture, however, we need a model of phase separation, which we call viscoelastic model . This model is likely a general model that can describe all types of isotropic phase separation including solid and fluid model as special cases. We point out that this dynamic asymmetry between the components is quite common in complex fluids, one of whose components has large internal degrees of freedom. We also demonstrate that viscoelastic phase separation in such dynamically asymmetric mixtures can be characterized by the order-parameter switching phenomena. The primary order parameter switches from the... 

Key words Viscoelastic effects - phase separation - critical phenomena -complex fluids - dynamic asymmetry... 

Here, we focus our attention on phase separation in complex fluids that are characterized by the large internal degrees of freedom. In all conventional theories of critical phenomena and phase separation, the same dynamics for the two components of a binary mixture, which we call dynamic symmetry between the components, has been implicitly assumed [1, 2]. However, this assumption is not always valid especially in complex fluids. Recently, we have found [3,4] that in mixtures having intrinsic dynamic asymmetry between its components (e.g. a polymer solution composed of long chain-like molecules and simple liquid molecules and a mixture composed of components whose glass-transition temperatures are quite different), critical concentration fluctuation is not necessarily only the slow mode of the system and, thus, we have to consider the interplay between critical dynamics and the slow dynamics of material itself In addition to a solid and a fluid model, we probably need a third general model for phase separation in condensed matter, which we call viscoelastic model . 

Gel model None Chemical gels Elasticity Topological dynamic asymmetry... 

Viscoelastic model None Polymer solutions Viscoelasticity Dynamic asymmetry... 

However, dynamic asymmetry can be introduced even for solid mixtures through the composition dependence of a diffusion constant. This is only the way to introduce dynamic asymmetry into solids there is no velocity field in solids. It should be noted that in the above argument dynamic asymmetry originates from the asymmetry in the mechanical properties between two components. Dynamic asymmetry is a prequisite to phase-inversion phenomena irrespective of whether a system is solid or fluid. 

Viscoelastic phase separation is expected to be universal in any mixture having asymmetry in elementary molecular dynamics between its components. The possible candidates for dynamic asymmetry are (1) slow dynamics in complex fluids such as polymer solutions and surfactant solutions, coming from their complex internal degree of freedom (e.g., entanglement effects in polyers) and (2) that near-glass transition. We hope that more examples of viscoelastic phase separation will be found in the family of complex fluids in the near future. 

Key words Viscoelastic phase separation - dynamical asymmetry - two-fluid model - smoothed-particle hydrodynamics... 

Now, we carry out the simulation by using the above model in two dimensions. In order to concentrate our efforts on examining the effect of dynamical asymmetry, we simplify the model assuming that F is the symmetric Ginzburg-Landau-type free energy and ta and G are... 

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