Membranes based on polyelectrolyte complexes (PECs) can
now be
prepared through several sustainable, organic solvent-free approaches.
A recently developed approach allows PECs made by stoichiometric mixing
of polyelectrolytes to be hot-pressed into dense saloplastics, which
then function as ion-exchange membranes. An important advantage of
PECs is that tuning their properties can provide significant control
over the properties of the fabricated materials, and thus over their
separation properties. This work studies the effects of two key parameters—(a)
ratio of mixing and (b) choice of polyelectrolytes—on the mechanical,
material, and separation properties of their corresponding hot-pressed
saloplastic-based ion-exchange membranes. By varying these two main
parameters, charge density—the key property of any IEM—was
found to be controllable. While studying several systems, including
strong/strong, strong/weak, and weak/weak combinations of polyelectrolytes,
it was observed that not all systems could be processed into saloplastic
membranes. For the processable systems, expected trends were observed
where a higher excess of one polyelectrolyte would lead to a more
charged system, resulting in higher water uptake and better permselectivities.
An anomaly was the polystyrenesulfonate–polyvinylamine system,
which showed an opposite trend with a higher polycation ratio, leading
to a more negative charge. Overall, we have found that it is possible
to successfully fabricate saloplastic-based anion- and cation-exchange
membranes with tunable charge densities through careful choice of
polyelectrolyte combination and ratio of mixing.