Cross-correlated humidity-dependent structural evolution of Nafion thin films confined on a platinum substrate.

Nanometer thin films of Nafion ionomer interfaced with platinum form the functional electrodes in many electrochemical devices including fuel cells and electrolyzers. To impart facile proton conduction in a Nafion ionomer, sufficient hydration of the Nafion ionomer is necessary to create a percolating network of water-filled nanometer-sized hydrophilic domains that manifest as macroscopic swelling. This hydration behavior of the ionomer thin films is poorly understood especially for films confined on electrochemically relevant Pt substrates.

Water uptake and swelling hysteresis in a nafion thin film measured with neutron reflectometry.

Water uptake and swelling in a thin (∼15 nm) Nafion film on SiO2 native oxide on a Si wafer is studied as a function of relative humidity (8-97%) at room temperature and as a function of temperature (25-60 °C) at 97% relative humidity by neutron reflectometry. This is the first report on the behavior of thin Nafion films at elevated temperatures and high humidity. Large hysteresis is observed during the temperature cycle.

Probing the hydration of ultrathin antifouling organosilane adlayers using neutron reflectometry.

Neutron reflectometry data and modeling support the existence of a relatively thick, continuous phase of water stemming from within an antifouling monoethylene glycol silane adlayer prepared on oxidized silicon wafers. In contrast, this physically distinct (from bulk) interphase is much thinner and only interfacial in nature for the less effective adlayer lacking internal ether oxygen atoms. These results provide further insight into the link between antifouling and surface hydration.

Effect of alloying magnesium with chromium and vanadium on hydrogenation kinetics studied with neutron reflectometry.

The effect of chromium and vanadium alloying on the hydrogenation of a magnesium thin film is studied by neutron reflectometry. Immediate formation of a blocking MgD(2) layer is observed in pure Mg, however in the alloyed film deuteration is rapid and almost completely homogeneous.

Ion distribution in multilayers of weak polyelectrolytes: A neutron reflectometry study.

Neutron reflectometry was used to determine the distribution of salt ions and water in thin poly(acrylic acid) and poly(allylamine hydrochloride) polyelectrolyte multilayers assembled with and without salt. Increasing salt concentration reverses the exclusion of water from the substrate region, eventually leading to an asymmetric segregation of water near the substrate at high salt concentration. The counterions were found to localize near the substrate in films that were either assembled with salt or were exposed to salt solutions.

Water distribution in multilayers of weak polyelectrolytes.

The water localization in thin polyelectrolyte multilayers assembled from poly(acrylic acid) and poly(allylamine hydrochloride) was investigated with neutron reflectivity in an atmosphere of controlled humidity and with bulk water. Water was found to be distributed asymmetrically within the multilayer and to localize preferentially at the polymer surface. The diffusion of water into the multilayer did not completely penetrate to the substrate, but instead there appeared to be an exclusion zone near the Si substrate.