PREPARATION OF ASYMMETRIC POLYSULFONE MEMBRANES - ANALYSIS OF THE FORMATION PROCESS

Integrally skinned asymmetric flat membranes of polysulfone were prepa red by wet phase inversion process. Scanning electron micrographs reve aled that these membranes consist of an ultrathin skin layer, a tightl y packed modular transition layer and two characteristic substructures underneath it: one is an open cell, sponge like substructure (polymer solution concentration higher than 10% w/w), and the other is a finge r-like substructure (polymer solution concentration 10% w/w). The tern ary phase diagrams of the system polysulfone/N,N-dimethylformamide/wat er and a mechanism based in different composition courses of a membran e volume element were used to explain membrane structure formation. It allows a qualitative explanation of three different structure formati ons.