Effects of mixture casting Nafion® with quaternary ammonium bromide salts on the ion-exchange capacity and mass transport in the membranes

Nafion® has been used to modify electrodes for a wide variety of electrochemical applications. This research studies how the physical properties of Nafion® are affected by mixture casting Nafion® with quaternary ammonium bromide salts of differing sizes and hydrophobicities. The quaternary ammonium bromides incorporated into Nafion® have shown up to a (6.73±1.49)-fold increase in the flux of tris(2,2′-bipyridyl) ruthenium(II) (Ru(bpy)32+) through a mixture cast (C2H5)4NBr/Nafion® membrane. The quaternary ammonium bromide incorporation can increase the pore size of Nafion® to allow for the electrochemical sensing of large redox moieties, such as erythromycin, which cannot be sensed at Nafion®-modified electrodes. One of the most startling effects of incorporating the quaternary ammonium bromide salts is the loss of selectivity upon incorporation of all tetraalkylammonium bromides. Along with this loss of selectivity, the number of available exchange sites to proton of the Nafion® membranes decreases with the increase in size and hydrophobicity of the quaternary ammonium bromides.