The pressure dependence of the interaction term in the Flory-Huggins-Staverman expression for the free enthalpy of mixing can be introduced with the aid of general thermodynamic relations. The peculiar pressure influence on the phase behaviour of the system polystyrene/cyclohexane, where the sign of (6 T/6p )c at the critical point changes upon an increase of pressure and molar mass of polystyrene, is taken as a test case for this semi-phenomenological (SP) model and for a modified form of the mean-field lattice-gas (MFLG) model published earlier. The SP model performs very well in describing one part of the phase diagram and in predicting another part. The MFLG model in contrast only represents data for polystyrene samples of different molar mass separately if one of the parameters for the mixture is made a function of the hole concentration. A simultaneous description for all samples is only qualitative even though the interaction term is made a highly complicated concentration function.
Посилання на статтю:
Mean-field lattice equations of state: 4. Influence of pressure on the phase behaviour of the system polystyrene/cyclohexane / L. van Opstal* and R. Koningsveld // Polymer. – 1992. – Vol 33. – P. 3433-3444.