Permeation of urea and water through sulfonated poly(styrene‐isobutylene‐styrene) membranes with counterion substitution

Abstract

AbstractThis study describes the influence of counterion substitution on the transport of urea and water through sulfonated poly(styrene‐isobutylene‐styrene) (SIBS) membranes. SIBS was sulfonated to 66.4% to allow for enough ionic domains to transport urea and water through the membrane. Counterions, including alkyl‐substituted ammonium ions, influenced the ionic domains creating a selective barrier that hindered the transport of urea and water through SIBS. Permeability measurements demonstrated that counterion substitution significantly affected the transport of urea. Membranes with higher charge counterions exhibited a more pronounced reduction in permeability due to the formation of crosslinks and increased restriction on molecular diffusion. Membranes substituted with ammonium salts showed reduced permeability due to the alkyl chains' hydrophobic nature, which created a physical barrier against the passage of urea molecules. Pure water flux tests indicated that counterion substitution also reduced the water flux of the membranes. Membranes with +1 counterions showed a small reduction in the water flux, while membranes with higher charge counterions and alkyl chain substitutions exhibited larger reductions, highlighting the influence of crosslinking and hydrophobicity on water transport.