Flory-Huggings parameter

It is clear from Equation (12.10) that when the Flory-Hugging interaction parameter, y, is less than 0.5 - that is, the chains are in good solvent conditions - then will be positive and the interaction repulsive, and wiU increase very rapidly with decreasing h, when the latter is lower than 25. This explains the strong repulsion obtained between water droplets surrounded by PHS chains. The latter are highly soluble in the hydrocarbon medium, and any attempt to overlap the chains results in very strong repulsion as a result of the above-mentioned unfavourable mixing. 

Many properties of pure polymers (and of polymer solutions) can be estimated with group contributions (GC). Examples of properties for which (GC) methods have been developed are the density, the solubility parameter, the melting and glass transition temperatures, as well as the surface tension. Phase equilibria for polymer solutions and blends can also be estimated with GC methods, as we discuss in Section 16.4 and 16.5. Here we review the GC principle, and in the following sections we discuss estimation methods for the density and the solubility parameter. These two properties are relevant for many thermodynamic models used for polymers, e.g., the Hansen and Flory-Hug-gins models discussed in Section 16.3 and the free-volume activity coefficient models discussed in Section 16.4. 

Solubility parameters can also be estimated from intrinsic viscosity. Flory [101] related intrinsic viscosity to polymer molecular weight and the chain-expansion factor. The chain-expansion factor can, in turn, be related to the polymer-solvent interaction parameter using the Flory-Hug-gins theory. A variety of models can be used to relate the interaction parameter to solubility parameters [87,102,103] these equations have the form... 

It has been shown that the extreme enhancement of strain at break for blends polycarbonate/poly(ethylene terephthalate) (PC/PET) is due to the corresponding structural changes of the indicated blends, which are characterized by their structure fractal dimension variation. The blends deformability rise can be achieved by enhancement of either Flory-Hug-gins interaction parameter, or shear strength of their autohesional contact. The transparence threshold of macromolecular coils achievement results in sharp reduction of strain at break, that is, its decrease practically up to zero. 

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