Polymeric
membranes are widely used for salt removal, but mechanism
of ion permeation is still insufficiently understood. Here we analyze
ion transport in polymers relevant to desalination, dense aromatic
polyamide Nomex and cellulose acetate (CA), using impedance spectroscopy,
focusing on the effects of the salt type, concentration and pH. The
results highlight the role of proton uptake in ion permeation. For
Nomex the exceptionally high affinity to proton results in a power-low
scaling of conductivity with salt concentrations with an unusual exponent
1/2. The results for CA suggest dominance of pore transport, with
pore charge increasing with decreasing pH, which contradicts previous
view of CA as a weakly acidic polymer and points to proton uptake
as possible pore-charging mechanism. The observed effects may have
far-reaching consequences in desalination, as even at neutral pH they
may both enhance and suppress salt permeation and affect pH changes
