Transport Properties of Cation-Exchange Membranes Obtained by Pore Filling of Track-Etched Membranes with Perfluorosulfonic Acid Polymer

In this paper the correlation between the structural characteristics and transport properties of pore-filling membranes formed by embedding an ion-conducting polymer into track-etched substrates was studied. Cation-exchange membranes were fabricated by filling the pores of track-etched membranes with a perfluorosulfonic acid polymer (trade mark LF-4SC). The resulting membranes differed in the volume fraction of the ion-conducting polymer and in the presence or absence of a surface LF-4SC layer. SEM and ATR-FTIR spectroscopy were employed to characterize the chemical composition and structure of the membranes. A comparative analysis of ion-exchange capacity and water uptake was carried out. Concentration dependences of specific electrical conductivity and diffusion permeability in NaCl solutions were obtained. The effects of pore filling degree and LF-4SC layer thickness on osmotic transport, diffusion permeability, and selectivity were analyzed. The electrical resistance of the prepared membranes was found to be comparable to that of the commercial MF-4SC membrane, produced from the same perfluorosulfonic acid polymer, despite a significant fraction of the polymer in the new membranes not participating in counterion transport. The observed structure–property relationships were interpreted within the framework of the two-phase microheterogeneous model, providing insight into the functional behavior of the composite membranes.