Method for producing a polyelectrolyte complex membrane

A method for producing a polyelectrolyte complex (PEC) membrane having a predetermined porosity via salt dilution induced phase separation, the method comprising the following steps:

• (i) providing a liquid polymer solution having a homogeneous single phase at an overcritical salt concentration, where the overcritical salt concentration is a salt concentration higher than the salt concentration at the critical point, by mixing polyanions and polycations in an aqueous medium, the liquid polymer solution containing the polyanions and polycations dissolved in the aqueous medium in a state where the polyanions and polycations do not form a polyelectrolyte complex (PEC), wherein the complexation of the polyelectrolyte is suppressed by the overcritical salt concentration of the liquid polymer solution, which is adjusted either by the addition of a salt before the mixing step and/or by the addition of the salt after the mixing step;
• and
• (ii) thereafter, without preparing the solid polyelectrolyte complex (PEC) or a coacervate phase, exposing the overcritical salt rich liquid polymer solution having a homogeneous single phase to an aqueous medium so as to decrease the salt concentration, which triggers the complexation of the polyelectrolyte and precipitation of the polyelectrolyte complex (PEC), thereby forming the polyelectrolyte complex (PEC) membrane,
• wherein the overcritical salt rich liquid polymer solution has a viscosity, measured as dynamic viscosity at room temperature using a rheometer, of 10 to 100000 mPa·s before exposing it to the aqueous medium in step (ii),
• wherein the salt concentration of the overcritical salt rich liquid polymer solution in step (i) is sufficiently high so that the formation of the solid polyelectrolyte complex (PEC) and of the coacervate phase can be suppressed, and
• wherein the method does not employ any organic solvent.