Chain Connectivity and Conformational Variability of Polymers: Clues to an Adequate Thermodynamic Description of Their Solutions, 2

In Part 1 of this contribution we have reported how the Flory‐Huggins interaction parameterχcan be modeled as a function of chain length within the composition range of pair interaction between the macromolecules by means of the three parametersα,ζ, andλ. This contribution presents the extension of the approach to arbitrary volume fractions,φ, of the polymer and its application to published data onχ(φ). The resulting equation readsχ = α(1 − νφ)−2 − ζ(λ + 2(1 − λ)φ) and requires only the additional parameterνto incorporate the composition dependence. Its employment to experimental data is very much facilitated by substituting forχo(limiting value forφ → 0); furthermore, the expression can in good approximation be simplified toχ ≈ (χ0 + ζλ)(1 − νφ)−2 − ζλ(1 + 2φ). That is: only two parameters,νand the product ofζandλ, need to be adjusted. This relation is capable of describing all types of composition dependencies reported in the literature, including the hitherto incomprehensible occurrence of pronounced minima inχ(φ). For a given system the evaluation of the chain length dependence ofχo, reported in Part 1, and the present evaluation of the composition dependence ofχyield the same data for the conformational responseζ. Similarly both types of measurements generate the same interdependence betweenζandα. The physical meaning of the different parameters and the reason for the observed correlations are discussed. Interrelation betweenζλandαfor the evaluated systems. magnified image Interrelation betweenζλandαfor the evaluated systems.