Effects of surfactants on the transport properties of redox species through Nafion ® membranes

Abstract

Previous research in our group has employed tetraalkylammonium bromides to alter the micellar structure of Nafion ® membranes to affect flux of redox species through the membrane. However, research by Patist et al. has shown that maximum micellar stability occurs when the chain lengths of the both the main micellar component and the surfactant are the same in sodium dodecyl sulfate micelles (SDS). When considering the steric hindrance of large, spherical ammonium salts and the effect of chain length compatibility on micellar stability, it was determined that n-alkyltrimethylammonium and n-alkyltriethylammonium surfactants may be more favorable in altering the pore structure. This research focuses on mixture-casting Nafion ® with ammonium-based surfactants in order to form more stable Nafion ® membranes with larger pore structures and a less acidic environment that will be more biocompatible with entrapping dehydrogenase enzymes within the membrane. n-Alkyltriethylammonium and n-alkyltrimethylammonium surfactants decreased the number of available exchange sites to proton (proton exchange capacity) of the membrane and they altered the transport of redox species through the membrane. Phenyltrimethylammonium bromide treated Nafion ® membranes and triethylhexylammonium bromide treated Nafion ® membranes were found to successfully immobilize dehydrogenase enzymes while maintaining enzyme activity.