Rheological and Physical Properties of Sulfonated Polystyrene Ionomer Solutions and the Membranes
Vol. 55, No. 1, pp. 56-62,
Feb. 2018
10.12772/TSE.2018.55.056
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Abstract
The rheological properties of sulfonated polystyrene (SPS) ionomer solutions were found to be significantly affected by solvent polarity, counterion, sulfonation level, and temperature. In the dilute concentration regime, the reduced viscosity (ηred) of SPS solutions in the dimethyl sulfoxide (DMSO), which is a polar solvent, increased with decreasing concentration, whereas opposite effects were observed in low-polarity solvent tetrahydrofuran (THF). H-SPS solutions in THF showed typical shear-thinning behavior over all the measured frequencies, while solutions in DMSO showed shear-thickening behavior at low shear rates, followed by shear-thinning behavior at higher shear rates. These different behaviors might result from differences in polymer–solvent interactions and the chain conformation. SPS solutions in DMSO containing monovalent ions (Na+) exhibited higher dynamic viscosity values than those with divalent ions (Ca2+, Mg2+) because of the different degrees of chain expansion. In DMSO, the dynamic viscosity increased with temperature, regardless of the sulfonation level and counterion. Both the proton conductivity and methanol permeability of the SPS membranes increased with increasing sulfonation level and exhibited an abrupt increase between 10 and 15 mol%, indicative of a percolation threshold.
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