Polymer blend phase behavior

Meredith JC, Karim A, Amis EJ (2000) High-throughput measurement of polymer blend phase behavior. Macromolecules 33 5760-5762... 

FIGURE 16 General phase diagram of polymer blends, phase behavior can be monitored in the window between and T, areas enclosed by the curves are regions of phase instability. 

Paul, D.R. (1985) Polymer blends. Phase behavior property relationship in Multicomponent Polymeric Materials (Eds D.R. Paul, LH. Sperling), AtAmices in Chemistry Series, 211, American Chemical Society, Washington D.C.,... 

Kipper, M.J. Seifert, S. Thiyagarajan, P. Narasimhan, B. Understanding polyanhydride blend phase behavior using scattering, microscopy, and molecular simulations. Polymer 2004, 45 (10), 3329-3340. 

In order to determine the phase behavior of heterogeneous polymer blends, phase diagrams are usually constructed in terms of the interaction parameter Xi2 and the composition or temperature and composition. Figure 3.2a represents the dependence of AG on as computed from the Flory-Huggins equation (Eq. (3.14)) for a symmetric binary blend (rj = V2 = r). The curves are shown for different values of Xi2> which is the only relevant parameter in the Flory-Huggins equation. For exothermic or adiabatic mixing G =J [Pg.101]

The miscibility limit between thermotropic liquid crystal polymers and flexible chain polymers can be predicted by calculations corresponding to the spinodal curve at constant temperature. This miscibility is increased with the increase of the degree of disorder (y/jc,) of the liquid crystal polymer and with the decrease of the degree of polymerization. Two quantitative parameters from the Hory s lattice theory can be used to estimate the phase behavior of this kind of blend at melt processing temperature the polymer-polymer interaction parameter and the degree of disorder (y/Xj). In binary polymer blends phase separation may occur for any value of degree of disorder (y/Xj)... 

Penning JP, Manley RSJ. Miscible blends of two crystalline polymers 1. Phase behavior and miscibility in blends of poly(vinylidene fluoride) and poly(l,4-butylene adipate). Macromolecules 1996 29(l) 77-83. 

Ternary Blends. Discussion of polymer blends is typically limited to those containing only two different components. Of course, inclusion of additional components may be useful in formulating commercial products. The recent Hterature describes the theoretical treatment and experimental studies of the phase behavior of ternary blends (10,21). The most commonly studied ternary mixtures are those where two of the binary pairs are miscible, but the third pair is not. There are limited regions where such ternary mixtures exhibit one phase. A few cases have been examined where all three binary pairs are miscible however, theoretically this does not always ensure homogeneous ternary mixtures (10,21). 

A variety of experimental techniques have been used to prepare and characterize polymer blends some of the mote important ones for estabHshing the equiHbtium-phase behavior and the energetic interactions between chain segments ate described here (3,5,28,29). 

The hterature contains extensive reports on investigations of the equiUbrium-phase behavior for an enormous number of polymer—polymer pairs (1,97). The number of blends known to be miscible has grown so rapidly since the mid-1980s that it is more instmctive to attempt to understand these observations in terms of the molecular stmctures of the components rather than to catalog them. 

Flow behavior of the polymer blends is determined by their structure, which is governed by the degree of dispersion of the component and by the mode of their distribution. For blends having identical compositions, it is possible to produce systems in which one and the same component may be either a dispersion medium or a dispersed phase [1]. This behavior of the polyblend systems depends on various parameters, the most important of which is the blending sequence. It is, therefore, difficult to obtain a uniform composition property relationship for the polymer blends even though the composition remains identical. 

The flow behavior of the polymer blends is quite complex, influenced by the equilibrium thermodynamic, dynamics of phase separation, morphology, and flow geometry [2]. The flow properties of a two phase blend of incompatible polymers are determined by the properties of the component, that is the continuous phase while adding a low-viscosity component to a high-viscosity component melt. As long as the latter forms a continuous phase, the viscosity of the blend remains high. As soon as the phase inversion [2] occurs, the viscosity of the blend falls sharply, even with a relatively low content of low-viscosity component. Therefore, the S-shaped concentration dependence of the viscosity of blend of incompatible polymers is an indication of phase inversion. The temperature dependence of the viscosity of blends is determined by the viscous flow of the dispersion medium, which is affected by the presence of a second component. 

Miscible Polymer Blends A subclass of polymer bends encompassing those blends that exhibit single-phase behavior. 

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