Strong correlation between membrane effective fixed charge and proton conductivity in the sulfonated polysulfone cation-exchange membranes

The effectiveness of fixed charge in sulfonated polysulfone membranes and its correlation with proton conductivity and physicochemical properties have been investigated in this work. The membranes were prepared with various concentrations of sulfonating agent (6% to 10% v/v) and followed by the characterizations that include membrane potential measurements, proton conductivity, and physicochemical properties (contact angle, water uptake, and ion-exchange capacity). Here, the effective fixed-charge concentrations of the membranes were obtained based on the data of membrane potential measurements using the Teorell-Meyer-Siever equation. The analysis results exhibit that a strong correlation between effective charge concentration and proton conductivity, which is expressed by the linear increase of proton conductivity with QX. This correlation is also supported by the membranes physicochemical data, such as water uptake, ionic exchange capacity, surface contact angle against water and functional analysis using FTIR. Finally, it was also developed an ionic conductivity equation that describes the correlation between proton conductivity and QX values.