Density and solubility of nafion: Recast, annealed, and commercial films

The density of Nafion membranes wetted in water and acetonitrile and the solubility of Nafion in a 50:50 ethanol/water mixture are reported, Commercially available membranes, solution recast membranes, and recast membranes thermally processed for varying lengths of time were examined. Unheated recast membranes were found to be similar to 20% less dense in water than both commercial membranes and recast membranes heated at 140 degrees C for 40, 50, and 60 min. For heating times of greater than or equal to 40 min, the density of recast membranes in water was invariant and equal to the density of commercial films. Similarly, in acetonitrile, commercial membranes and films heated for 1 h had the same density; unheated recast films were similar to 25% less dense. Nafion density in acetonitrile was similar to 15% less than that in water. Acid pretreatment reduced Nafion film density by similar to 15%. Unheated recast films were 22-100% soluble in a sonicated ethanol/water mixture. Commercial membranes and recast films heated for as little as 10 min were insoluble under the same conditions.