Miscibility thermodynamic

Ch and MEK are two different solvents, but having almost the same solubility parameter (18.76 and 18.91 MPa1/2, respectively) hence, they are thermodynamically miscible. According to Hildebrand, the enthalpy of mixing can be related to the solubility parameter as ... 

Without doubt the simple mixing of two or more polymers is the easiest, most direct and the cheapest way of producing new materials. However, the properties of such mixtures are very dependent on the miscibility of the components. Of the few polymer pairs which are thermodynamically miscible, some examples are ... 

While these equations are crude approximations describing the actual behaviors of various polymeric systems, they have widespread experimental viability [123]. These equations assume that the systems are thermodynamically miscible and stable. Equations resolving the solubility parameters of mixtures can also be done using Small s or Fedors methods [124,125]. This latter method only requires the knowledge of the structural formula of the compounds whereas Small s method requires experimental determination of the molar volume. 

Although some miscible systems exhibit Tg-composition dependencies as defined by these simple equations, many blends cannot be correlated by them or any of the other well known expressions such as the Kelly-Bueche, Gordon-Taly-lor or the Gibbs-Dimarzio relationships [126-128]. However, the existence of thermodynamic miscibility has not been proven for epoxy-polyimide systems. 

In the field of thermoplastic immiscible blends, the emulsifying activity of block copolymers has been widely used to solve the usual problem of large immiscibility associated with high interfacial tension, poor adhesion and resulting in poor mechanical properties. An immiscible thermoplastic blend A/B can actually be compatibilised by adding a diblock copolymer, poly(A-b-B) whose segments are chemically identical to the dissimilar homopolymers, or poly(X-b-Y) in which each block is chemically different but thermodynamically miscible with one of the blend component. Theoretical... 

DiPaola-Baranyi, G., "Thermodynamic Miscibility of Various Solutes with Styrene-Butyl Methacrylate Polymers and Copolymers," Macromolecules, 14, 683 (1981). 

DiPaola-Baranyi, G. Richer, J. Prest, W. M., "Thermodynamic Miscibility of Polystyrene-Poly-(2,6-dimethyl- 1,4-phenylene oxide) Blends.," Can. J. Chem., 63, 223 (1985). 

Blends of polystyrene and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) can be mixed in the melt as both polymers have reasonable thermal stability. There has however been much discussion as to whether the blends are truly one phase. Some techniques suggest homogeneity while others suggest a heterogeneous structure. On balance it appears that the two polymers are in fact thermodynamically miscible in all proportions but completely efficient mixing is difficult to achieve... 

As stated earlier this method is the commonest method of preparing homogeneous blends in academic studies. It is however not without its pitfalls. Two phase blends can be formed by the evaporation of solvent from solutions of polymers which are themselves thermodynamically miscible. 

It was observed that the polymer layers used for the SANS experiment could not be separated after contact had been maintained for several hours, the interface between the two sheets having been eliminated by the inter-diffusion. Such an increase in peel adhesion with contact time have in fact been directly measured for these blends [1,5]. Notwithstanding the broad glass transitions, the inter-diffusion revealed by both the SANS and adhesion experiments provides direct evidence of the thermodynamic miscibility of the blend. 

Figure 5 - Small angle neutron differential scattering cross section (ooo) measured from a sample consisting of sheets of PIP (N = 23000) and deuterated 1,2-PBD (N = 3200) which were in contact for 162 hours at 52°C. The scattering contrast significantly exceeds the incoherent background (—) determined from measurements on the individual polymers, evidencing the thermodynamic miscibility of the blend.

Belfiore, L.A. Cooper, S.L. Thermodynamic miscibility in polymer-polymer and polymer-diluent blends. J. Polym. Sci. Polym. Phys. Ed. 1983, 21, 114-115. 

IGC was used to determine the thermodynamic miscibility behavior of several polymer blends polystyrene-poly(n-butyl methacrylate), poly(vinylidene fluoride)-poly(methyl methacrylate), and polystyrene-poly(2,6-dimethyl-1,4-phenylene oxide) blends. Specific retention volumes were measured for a variety of probes in pure and mixed stationary phases of the molten polymers, and Flory-Huggins interaction parameters were calculated. A generally consistent and realistic measure of the polymer-polymer interaction can be obtained with this technique. 

Blends of polystyrene/poly(2,6-dimethyl-l,4-phenylene oxide) and polystyrene/poly(vinyl methyl ether) were investigated by IGC over wide composition and temperature ranges. Flory-Huggins free energy parameters were obtained and are discussed as the criterion for thermodynamic miscibility. From the temperature variation of the free energy parameter, phase diagrams for both blends were obtained. 

A solid-state C NMR study of the intermolecular hydrogen bonding formation in a blend of phenolic resin and poly(hydroxyl ether) of bisphenol A was reported by Wu et at) " The presence of a single glass transition temperature for all of the blend samples with different composition as disclosed by the DSC measurements demonstrates that the blends are thermodynamically miscible. The solid state NMR parameters, including chemical shift, efficiency of cross-polarization and Ti, confirm the presence of more free OH groups when one of the polymers is the minor component. 

The most basic question when considering a polymer blend concerns the thermodynamic miscibility. Many polymer pairs are now known to be miscible or partially miscible, and many have become commercially Important. Considerable attention has been focussed on the origins of miscibility and binary polymer/polymer phase diagrams. In the latter case, it has usually been observed that high molar mass polymer pairs showing partial miscibility usually exhibit phase diagrams with lower critical solution temperatures (LCST). 

In any case, the prepolymer synthesis results in somewhat better defined domains, characterized by the relative translucency of the prepolymer route material relative to the one-shot route, and as illustrated in the transition behavior. Figure 3. Better defined domains mean a purer rubber phase, which in turn may yield greater toughness to this form of the material. Important questions as to the development of intermediate Tg s with extensive interfacial boundary material (48) or on complete thermodynamic miscibility (49) remain for the future. 

The solid phase of bread crumb can be viewed as a composite material where amylose, amylopectin and protein form separated phases due to poor thermodynamic miscibility of the different polymers. Composites are characterized by exhibiting mechanical properties that cannot be achieved with the individual constituents alone, but are dependent on the interface between the components. A sharp interface as found between starch and protein provides strong evidence of little polymer interdiffusion and weak interfacial adhesion.14 The present results suggest that starch forms a continuous phase in bread which has also been confirmed with confocal scanning laser microscopy.15 The presence of a protein phase reduces the continuity of the starch phase and, thus, reduces the cohesion of the material as revealed by a comparison of the breaking stresses of aged flour and starch gels (data not shown).16... 

Silberberg and Kuhn, 1952 Wolf, 1980, 1984]. Many others estimates fall within these limits [e.g., Kaplan, 1976 Bair and Warren, 1980 Cowie, 1989]. Thus, it seems that the true, thermodynamic miscibility is associated with the size of compositional heterogeneity d < 10 nm. 

Erom Dj one may calculate the binary interaction parameter, hence determine conditions for the thermodynamic miscibility. Figure 2.21 show the dependence on T and ((). 

In polymer blends, the thermodynamic miscibility depends primarily on specific interactions. For the entropic reasons, high molecular weight... 

Thermodynamic miscibility between the components such as in the case of polystyrene (PS) and poly(2,6-dimethyl 1,4-phenylene ether) (PPE) blends. 

Polyvinylidenefluoride (PVDF) and polymethylmethacrylate have been known to be a thermodynamically miscible blend exhibiting a single T, an indication of a single phase behavior [Bernstein et al., 1977 Mijovic et al., 1982]. A commercial PVDF/PMMA blend film (Fluorex A, Rexham Corp.) produced captively by solvent casting is used in specialty applications, such as a protective and decorative overlaminated for... 

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