Chemically modified carbon supports for the cathode catalyst layers of polymer electrolyte fuel cells (PEFCs) show considerable promise for boosting the oxygen reduction reaction. This study evaluated the ionomer distribution of Nafion ionomer thin films on nitrogen (N)modified carbon surfaces along their depth direction. Neutron reflectivity (NR) measurements performed using the double-contrast technique with H 2 O and D 2 O revealed that the introduction of N functional groups to carbon thin films promoted ionomer adsorption onto the surface under wet conditions (22 °C, 85% relative humidity). Molecular dynamics (MD) simulations conducted to verify the origin of the robust contact between the ionomer and N-modified carbon surface revealed an ionomer adsorption mechanism on the N-modified carbon surfaces, which involved Coulomb interactions between the positively charged carbon surface and the ionomer side chains with negatively charged sulfonic acid groups. The positive surface charge, which was determined using the contents of the N functional groups estimated by X-ray photoelectron spectroscopy, was found to be sufficient as an impetus for ionomer adsorption. This strategy involving NR measurements and MD simulations can provide insights into the solid−ionomer interfacial structures in a cathode catalyst layer and can therefore be extensively employed in studies on PEFCs.

This study aims to develop a molecular dynamics (MD) simulation procedure to investigate the wettability of primer-treated Al2O3 surfaces by bisphenol A diglycidyl ether (BADGE) and to understand the interaction between the surface and the liquid. The MD simulation results were compared with those obtained by contact angle measurements, time-of-flight secondary ion mass spectrometry (TOF-SIMS), and atomic force microscopy (AFM) and were found to be in agreement with the experimental evaluations. The results obtained from both the MD simulations and the experiments suggest that the configuration of the primers on the surface affect its wettability. In other words, silanes lying flat on the surface, such as mercapto silane, make it easy for BADGE to access any polar functional groups of the silane, thereby leading to a strong interaction and good wettability. For amino silane, although the configuration is similar to that of mercapto silane, its amino groups are bound to the surface owing to their high polarity, which results in a reduced accessibility for BADGE and a relatively poor wettability in comparison with mercapto silane. On the contrary, for silanes that stand up on the surface, including trifluoroalkyl silane, BADGE is hindered from approaching the silanol groups and interacting with them, and the surface shows poor wettability.

No abstract

Molecular dynamics simulations are used to study the fracture mechanism of the joining interface of a polymer and metal oxide. A polyphenylene sulfide (PPS) layer is sandwiched between two plates of aluminum oxide and one of the plates is pulled to simulate fracture under tensile force. The stress-strain curve for the polymer-metal interface is similar in shape to the stress-strain curve for constant cross-sectional strain in bulk PPS. In the simulations, fracture of the polymer-metal joint is initiated by the formation of small voids inside the polymer layer, which occurs at the yield point of the polymer-metal interface. Annealing prior to tensile loading is determined to enhance the joint strength.