Quick and reliable routes to phase diagrams for polyethersulfone and polysulfone membrane formation

Phase diagrams were measured and calculated for the ternary membrane formin g systems DMF/water/polysulfone and DMF/water/polyethersulfone at different temperatures. Customary experiments yielded cloud point curves, tie lines, and critical compositions. The theoretical computation starts from the Flo ry-Huggins theory and employs binary interaction parameters g(ij) that vary with the composition. This information was mainly obtained by means of Hea dspace-Gas Chromatography (HSGC, yielding the partial pressures of the vola tile components); these data were complemented by light scattering and swel ling experiments. The calculation of binodals, spinodals, tie lines, and cr itical points avoids the elaborate use of chemical potentials and minimizes the Gibbs energy directly. In order to reach total agreement between measu red and calculated ternary phase diagrams it is necessary to adjust the int eraction parameter between the polymers and water. Discrepancies between th e values obtained in this way and the values resulting from measurements wi th the binary subsystems indicate the necessity of ternary interaction para meters g(ijk).