Nafion™ dryers contain one or more strands of Nafion™ tubing. Most of the Nafion™ tubing wall is inert fluorocarbon polymer, and does not participate in the process. Since sulfonic acid is ionic in character and the bulk material is not, the sulfonic acid group within the Nafion™ tend to clump together. The activation process for Nafion™ reorients its sulfonic acid groups together into ionic channels extending from one side of the tubing wall to the opposite side.
When water strikes an exposed sulfonic acid group on the surface of the tubing, the water is initially bound by the surface group. Additional sulfonic acid groups deeper in the wall have less water attached to them, and consequently a higher affinity for water. Water molecules absorbed onto the surface of the tubing are therefore quickly passed on to underlying sulfonic acid groups, until the water reaches the opposite side. The water molecule then perevaporates into the surrounding medium. This process continues until the water vapor pressure gradient across the tubing wall is eliminated. If a very low water vapor pressure is maintained outside the tubing wall, water will stream across the tubing wall very quickly.
This is a First Order Kinetic reaction, and it proceeds very rapidly. Water is removed from a gas stream directly from the vapor phase, and is released into the surrounding environment directly to the vapor phase. There is no net phase change, and energy is thus not consumed by the process.