ATR-FTIR spectroscopic studies of the structure and permeability of sulfonated poly(ether sulfone) membranes. Part 1.—Interfacial water–polymer interactions

Abstract

Attenuated total reflection (ATR) FTIR spectroscopy has been used to monitor, in situ, the penetration of water into thin sulfonated poly(ether sulfone) films of different thicknesses. Water and polymer IR bands have been analysed to provide information about the molecular state of both diffusant and diffusion medium at the polymer/liquid interface. The hydration process is characterised by intensity enhancements in the aromatic ring and ν_s(SO₃^–) vibrational bands of the polymer and by dramatic changes of shape in the ν(OH) profile. These changes have been interpreted in terms of the changing water–polymer interactions as a function of hydration level. In particular, hydration causes considerable electronic perturbation of the conjugated polymer backbone through an ionisation process at the —SO₃H groups, giving rise to a stronger interaction between polymer and water and a reduced degree of hydrogen bonding between sorbed water molecules.