6533b7d3fe1ef96bd12611fa

RESEARCH PRODUCT

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

subject

description

Phase diagrams were measured and calculated for the ternary membrane forming 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 Flory-Huggins theory and employs binary interaction parameters g ij that vary with the composition. This information was mainly obtained by means of Headspace-Gas Chromatography (HSGC, yielding the partial pressures of the volatile components); these data were complemented by light scattering and swelling experiments. The calculation of binodals, spinodals, tie lines, and critical points avoids the elaborate use of chemical potentials and minimizes the Gibbs energy directly. In order to reach total agreement between measured and calculated ternary phase diagrams it is necessary to adjust the interaction parameter between the polymers and water. Discrepancies between the values obtained in this way and the values resulting from measurements with the binary subsystems indicate the necessity of ternary interaction parameters g ij .