Asymmetric polysulfone and polyethersulfone membranes: effects of thermodynamic conditions during formation on their performance

Membranes of polysulfone (PSU) and polyethersulfone (PES) were prepared from ternary and quaternary mixtures containing N,N-dimethylformamide (DMF) as solvent, water as non-solvent, and acetone (AC) as additive. The conditions for phase inversion and the desired phase separation mechanisms were selected on the basis of the phase behavior determined for the solvent/non-solvent/polymer systems. The influences of the composition of the casting solution, of the support, and of film thickness on structure and permeation properties of the membranes were analyzed by scanning electron microscopy (SEM) plus flux and separation experiments. The mechanisms of phase inversion that should prevail under the different conditions according to the measured phase diagrams were corroborated by means of light scattering experiments.