Chapter 3 - Statistical Thermodynamics of Polymer Blends

Abstract

Publisher Summary This chapter presents an overview of the development, comparison, and application of Flory and lattice fluid theories. The Flory and lattice fluid theories represent promising alternatives to the solubility parameter approach for predicting polymer compatibility, which means thermodynamic miscibility. The Flory theory demonstrates that mixture thermodynamic properties depend on the thermodynamic properties of the pure components. In particular, lower critical solution temperatures (LCST) behavior can be understood in terms of the dissimilarity of the equation of state properties of polymer and solvent. In the Flory theory, each pure component is characterized by three equations of state parameters: (1) a characteristic temperature T*, (2) a characteristic pressure p*, and (3) a characteristic specific volume vsp*. The lattice fluid theory does not require separation of internal and external degrees of freedom as does the Flory theory and Prigogine corresponding state theories. Both the Flory and lattice fluid theories require three equations of state parameters for each pure component. For mixtures, both the theories reduce to the Flory–Huggins theory at very low temperatures. According to the lattice fluid theory, a fluid is completely characterized by three molecular parameters: (1) ɛ*, (2) ν*, and (3) r or equivalently, the three equation of state parameters T*, p*, and ρ*. The chapter presents the complete thermodynamic description of the model fluid. In both the theories, for the sake of clarity, only the results for binary mixtures are presented.