Viscoelastic behavior polymer blends

With these generally accepted, but not necessarily accurate, conceptual models in hand, major efforts are going into molecular modeling of more complex real behavior. This is the state of the art. Some important areas of current work include nonlinear viscoelasticity, branched polymers, blends of different molecular weights, and chemical composition. E)eep problems remain, such as the definitive explanation of the 3.4 power law for the molecular weight dependence of melt viscosity and proper description of concentrated solution rheology. 

Binary fluorides, methods of preparing noble-gas, 77 335-336 Binary heterogeneous polymer blends compliance of, 20 347-348 moduli of, 20 346-347 nonlinear viscoelastic behavior of, 20 348 yield and/or tensile strength of, 20 348-349... 

Takayanagi, M., Harima, H., and Iwata, Y. (1963). Viscoelastic behavior of polymer blends and its eomparison with model experiments. Mem. Faculty Eng. Kyushu Univ. 23, 1-13. 

This book is concerned mainly with the study of the viscoelastic response of isotropic macromolecular systems to mechanical force fields. Owing to diverse influences on the viscoelastic behavior in multiphase systems (e.g., changes in morphology and interfaces by action of the force fields, interactions between phases, etc.), it is difficult to relate the measured rheological functions to the intrinsic physical properties of the systems and, as a result, the viscoelastic behavior of polymer blends and liquid crystals is not addressed in this book. 

If the rheology of suspensions and emulsions is difficult to describe theoretically and to determine experimentally, in the case of polymer blends these difficulties reach another order of complication. It suffices to note that in blends both phases are viscoelastic, the viscosity ratio varies over a wide range, and morphology can be very complex. To understand the rheological behavior of blends, it is useful to refer to simpler systems that can offer important insight. The following systems (Table 7.2) are commonly considered and will be treated in the following discussion. 

Blending two immiscible polymers always creates the third phase — the inteiphase. In binary blends, thickness of this third phase, AZ, is inversely proportional to the interfacial tension coefficient, When the blend approaches miscibility, approaches zero and AZ goes to infinity. Thus the interphase, with its own set of characteristic parameters e.g., viscoelasticity) may dominate the behavior of nearly miscible systems, as well as that of compatibilized blends. For further details on this topic see Chapter 4. Interphase and Compatibilization of Polymer Blends. 

The linear viscoelastic behavior of the pure polymer and blends has already been described quantitatively by using models of molecular dynamics based on the reptation concept [12]. To describe the rheological behavior of the copolymers in this study, we have selected and extended the analytical approach of Be-nallal et al. [13], who describe the relaxation function G(t) of Hnear homopolymer melts as the sum of four independent relaxation processes [Eq. (1)]. Each term describes the relaxation domains extending from the lowest frequencies (Gc(t)) to the highest frequencies (Ghf( )), and is well defined for homopolymers in Ref [13]. 

Generally PSAs are well known for their very viscoelastic behavior, which is necessary for them to function properly. It was therefore important to characterize first the effect of the presence of diblocks on the linear viscoelastic behavior. Since a comprehensive study on the effect of the triblock/diblock ratio on the linear viscoelastic properties of block copolymer blends has recently been reported [46], we characterized the linear viscoelastic properties of our PSA only at room temperature and down to frequencies of about 0.01 Hz. Within this frequency range all adhesives have a very similar behavior in terms of elasticity, as can be seen in Fig. 22.10. The differences appear at low frequency, a regime where the free iso-prene end of the diblock chain is able to relax. This relaxation process is analogous to the relaxation of an arm of a star-like polymer [47], and causes G to drop to a lower plateau modulus, the level of which is only controlled by the density of triblock chains actually bridging two styrene domains [46]. 

In Chapter 3, we used the Rouse model for a polymer chain to study the diffusion motion and the time-correlation function of the end-to-end vector. The Rouse model was first developed to describe polymer viscoelastic behavior in a dilute solution. In spite of its original intention, the theory successfully interprets the viscoelastic behavior of the entanglement-free poljuner melt or blend-solution system. The Rouse theory, developed on the Gaussian chain model, effectively simplifies the complexity associated with the large number of intra-molecular degrees of freedom and describes the slow dynamic viscoelastic behavior — slower than the motion of a single Rouse segment. 

Utracki, L.A. (1988) Viscoelastic behavior of polymer blends. Pdiym. Eng. Sci.,... 

Graebling, D., Muller, R., and Palierne, J.F. (1993) Linear viscoelastic behavior of some incompatible polymer blends in the melt interpretation of data with a model of emulsion of viscoelastic liquids. Macromolecules. 26 (2), 320-329. 

Mani, S., Malone, M.F., and Winter, H.H. (1992) Influence of phase separation on the linear viscoelastic behavior of a miscible polymer blend./. Rheol., 36 (8), 1625-1649. 

P.J. (1997) Linear viscoelastic behavior of molten polymer blends a comparative study of the Palierne and the Lee and Park models. Rhed. Acta, 36 (4),... 

The template behavior of the nanodispersed structure in the course of the foaming process was confirmed by Nemoto et al. [89] in the case of nanostructured polymer blends with extremely high differences in CO2 solubility and viscoelastic properties of both phases (PP and rubber). In these blends the homogeneous nucleation mechanism inside the PP matrix can be considered completely hindered. This kind of behavior can be applied to amorphons polymers (eg, PMMA, PS) combined with ideal nucleant nanostructures. 

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