Interaction parameters

For the modeling of phase diagrams and interfacial tensions it is essential to dispose of closed mathematical expressions describing the Gibbs energies of mixing as a function of composition, temperature, pressure and the molar masses of the polymers. Unfortunately theoretical predictions resting exclusively on the equations of state of the pure components prove inadequate. For that reason experimental information on the systems of interest are in many cases simply cast into Flory-Huggins interaction parameters and their dependence on the variables of state. Two fundamental deficiencies show up in this context: Firstly, the fact that the segments of macromolecules cannot be evenly distributed on the system at low polymer concentration and, secondly, the variable shape of such solutes. The consequences of the latter reality have already been studied in detailed and led to the concept of dimensional (conformational) relaxation.