Nafion® membranes were developed by DuPont, a perfluorosulfonic acid/polytetrafluoroethylene copolymer. These membranes are hydrophilic and the water is preferentially sorbed into the clusters due to the hydrophobic character of fluorocarbon matrix. The sulfonic acid groups are chemically active and fixed within the Teflon polymer matrix. Thus, this first synthetic ionic polymer is chemically resistant and durable, making it useful for Proton Exchange Membrane fuel cells. In order to monitoring the groups -OH of the Nafion®, we used the Photoacoustic Spectroscopy phases. The optical absorption spectrum was determined for wavelengths of 800 to 2600 nm. The procedure was to measure the samples in different hydration times. Using the Phase-Resolved Photoacoustic method, it was possible to separate the contribution of –OH, of C=O and of methylene group. The phase lag as a water function behaviors found may be associated with structural changes induced by membrane hydration.

The Nafion membranes are widely used in electrochemical applications such as fuel cells, chlor-alkali cells, and actuators-sensors. In this work, the thermal-optical characterization of Nafion in acid form was performed by photoacoustic spectroscopy, thermogravimetry, and differential scanning calorimetry. In the experimental procedure three distinct hydration levels were considered: (1) pristine membrane (λ ≅ HO/-SOH ≅ 5.6); (2) swelling process (λ ≅ 17.4); and (3) drying at controlled room temperature after swelling process (λ ≅ 6.5). The discovered behaviors showed significant irreversible structural changes induced by water retention in the membrane. These structural changes depend on the water population present in the clusters and also affect the directional thermal diffusivity of the membrane irreversibly.