Effect of Additives on Self-Assembling Behavior of Nafion in Aqueous Media

The dynamic light scattering technique is employed to study the self-assembling behavior of Nafion in dilute aqueous solutions and in water-based mixture solvents. The mixture solvents contain either salt or a small amount of glycerol, which is often necessary for the fabrication of the electrode−membrane assembly. Two kinds of aggregates are found in Nafion aqueous solutions: (1) an intrinsic aggregate (∼150 nm) due to the hydrophobic interaction of fluorocarbon backbone, which is found to be always present in aqueous solutions; (2) a larger, secondary aggregate, which can be suppressed by the addition of salt or a small amount of glycerol. This secondary/higher level aggregation may arise from the electrostatic attraction through the nonionized ion pairs, which are believed to facilitate the formation of large ion clusters and provide the ion connection between the ion clusters. We discuss the structures of Nafion aggregates based on the rodlike microstructure units and propose a microgel-type aggregation model.