Structural and electrochemical studies of heterogeneous ion exchange membranes based on polyaniline-coated cation exchange resin particles

Abstract

The idea to modify polystyrene sulfonated divinyl benzene (PSS/DVB) resin particles with electroactive polyaniline (PANI) prior to incorporating these into a polymer matrix (PVC in the present case) has been trialed in this study. The extent of PANI layering on resin particles was controlled by changing polymerization time during aniline polymerization reaction. The PANI modified PVC–PSS/DVB heterogeneous cation exchange membranes were characterized for their morphological, physical and structural properties using scanning electron microscopy (SEM), measurements of water uptake and ion exchange capacity, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). SEM micrographs showed PANI layering around PSS/DVB particles and shape change depending on aniline polymerization time that has been also confirmed by FTIR spectra through growing PANI peaks. PANI layering around resin particles resulted in lower water uptake of PANI modified resin membranes as compared to unmodified PVC–PSS/DVB membranes. The ion exchange capacity decreased initially at shorter PANI deposition times and increased slightly on prolonged deposition because of the cation character of doped PANI that was originated by excessive layering around the particles. TGA curves showed PANI degradation in addition to PVC and PSS/DVB resin degradations thus decreasing the overall thermal stability of PANI modified membranes. Ion transport studies in a two-compartment cell showed significantly different transport numbers for monovalent (Na⁺) and divalent (Ca²⁺) cations that decreased by increasing PANI layering around resin particles. The difference between transport numbers, a measure of membrane permselectivity, increased by increasing PANI deposition showing the strong screening effects of PANI layering.