RESUMEN
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 H2O and D2O 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.
RESUMEN
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.
RESUMEN
Detailed knowledge of the water status in living organisms is crucial for understanding their physiology and pathophysiology. Here, we developed a technique to spectroscopically image water at high resolution using ultrabroadband multiplex coherent anti-Stokes Raman scattering (CARS) microscopy equipped with a supercontinuum light source. This system allows for the visualization of a wide spectrum of CARS signals from the fingerprint to the end of O-H stretching at a spectral resolution of â¼10 cm-1. Application of the system to living mammalian cells revealed a spectral red shift of the O-H stretching vibrational band inside compared to outside the cells, suggesting the existence of stronger hydrogen bonds inside the cells. Furthermore, potential changes in spectra were examined by adding mannitol to the extracellular solution, which increases the osmolality outside the cells and thereby induces dehydration of the cells. Under this treatment, the red shift of the O-H stretching band was further enhanced, revealing the effects of mannitol on water states inside the cells. The methodology developed here should serve as a powerful tool for the chemical imaging of water in living cells in various biological and medical contexts.
