Calculation of Pressure−Temperature Diagrams and Distance for Phase Transition in Polyethylene Solutions

Understanding the phase behavior of polymer solutions is of great theoretical and practical importance. Pressure versus temperature (P−T) isopleths allow one to determine the number of phases present at a given T, P, and overall mixture composition. In this work, the PC-SAFT (perturbed-chain statistical associating fluid theory) equation of state (EOS) was applied to simulate the curves that describe the boundaries between several distinct regions depicted in P−T isopleths. A new strategy was used, and the simulation results were found to show good agreement with experimental cloud-point isopleth data from the literature. In addition, a method was developed to calculate the distance between an operating point (pressure and temperature) and the corresponding point in the interface for fixed molecular weight and weight fraction of the polymer.