Polarized Neutron Reflectometry of Nickel Corrosion Inhibitors.

Polarized neutron reflectometry has been used to investigate the detailed adsorption behavior and corrosion inhibition mechanism of two surfactants on a nickel surface under acidic conditions. Both the corrosion of the nickel surface and the structure of the adsorbed surfactant layer could be monitored in situ by the use of different solvent contrasts. Layer thicknesses and roughnesses were evaluated over a range of pH values, showing distinctly the superior corrosion inhibition of one negatively charged surfactant (sodium dodecyl sulfate) compared to a positively charged example (dodecyl trimethylammonium bromide) due to its stronger binding interaction with the surface. It was found that adequate corrosion inhibition occurs at significantly less than full surface coverage.X-ray photoelectron spectra were obtained at the National Engineering and Physical Sciences Research Council (EPSRC) XPS User’s Service (NEXUS) at Newcastle University, an EPSRC midrange facility. NR data were obtained on the D17 instrument, and samples were treated in the laboratories of the Partnership for Soft Condensed Matter (PSCM) at the Institut Laue-Langevin. M.H.W. is grateful for funding from the Oppenheimer Trust.This is the final version of the article. It first appeared from the American Chemical Society via http://dx.doi.org/10.1021/acs.langmuir.5b0171

Electrochemical SERS study of a biomimetic membrane supported at a nanocavity patterned Ag electrode

Lipid bilayers in which two leaflets were made of dimyristoyl- phosphatidylcholine (DMPC) and hybrid bilayers with one leaflet composed of hydrogenated lipid and another leaflet of deuterium substituted molecules (d63-DMPC) were deposited on highly ordered nanocavity patterned Ag electrodes using LB-LS and vesicle fusion techniques. In situ electrochemical surface enhanced Raman scattering (EC-SERS) was then used to study potential driven changes in these model biological membranes. The nanocavity structures provided a SERS active substrate with uniformly distributed surface enhancement. To ensure that the bilayer was separated from the metal surface by a hydrophilic space layer, the electrodes were chemically modified with a self-assembled monolayer (SAM) of \u3b2-thioglucose (TG) molecules. The monolayer of TG ensured that the solid substrate surface was hydrophilic. The electrochemical properties of the bilayer were monitored by recording differential capacitance curves. EC-SERS indicated that at the silver surface modified by the monolayer of TG the lower leaflet (in contact with the support) is more ordered than the top leaflet that is contact with solution. However, both leaflets remained in the liquid crystalline (LC) state for the entire range of investigated potentials. The results of this study show that the DMPC bilayer at the nanocavity patterned Ag surface may be used as a good biomimetic membrane model in future SERS studies of membrane proteins. The information concerning the effect of the electrode potential on membrane stability may be useful for the development of biosensors.\ua9 2013 Published by Elsevier Ltd.Peer reviewed: YesNRC publication: Ye

Hydrogen absorption into titanium under cathodic polarization: An in-situ neutron reflectometry and EIS study

Hydrogen (deuterium) absorption into sputter-coated titanium (Ti) film electrodes during cathodic polarization in heavy water (D2O) was monitored using in-situ neutron reflectometry (NR) and electrochemical impedance spectroscopy (EIS). The scattering length density (SLD) of Ti metal increased with increasing cathodic polarization, due to the penetration of deuterium through the surface oxide and into the underlying metal. The rate of D absorption estimated from the NR data showed a pattern with four distinctive regions separated by potential boundaries between -0.35 and -0.4 VSCE and around 3c-0.6 VSCE. EIS results support division of the behavior into these potential ranges. Hydrogen absorption by Tiwas observed at potentials < 3c-0.35 VSCE, where the capacitance and resistance of the TiO2 layer dramatically changed. At this point, the D content of the film quickly achieved a level of 3c900 ppm by weight (atom ratio D:Ti 3c 0.04). Decreased absorption kinetics were observed over the potential region from 3c-0.40 VSCE to -0.6 VSCE, indicating that D absorption was controlled either by a diffusion process through the TiO 2 layer or by the formation of blocking hydrides at the Ti/TiO 2 interface, at the base of the defective locations in the oxide through which the hydrogen was entering. Significant increases in the current density and SLD of the Ti film at potentials more negative than -0.6 V SCE were assigned to widespread hydrogen absorption and TiH x growth within the metal. These observations are consistent with hydrogen ingress through the oxide film, probably via weak points containing electronic defects and disorder, such as grain boundaries and triple points, at potentials as mild as 3c-0.4 VSCE, and with hydrogen penetration through continuous, intact oxide via the previously published redox transformation mechanism, at potentials more negative than -0.6 VSCE. \ua9 2013 The Electrochemical Society. All rights reserved.Peer reviewed: YesNRC publication: Ye

The penetration depth of chemical reactions in a thin-film Co 3O4 supercapacitor electrode

An experiment designed to measure the thickness of an electrochemically active layer on the surface of a thin-film Co3O4 electrode shows that the entire thickness of the film, 40 nm in all, undergoes chemical changes. This was the case when the film was first exposed to pure water and later subjected to +1 VSCE in 0.01M KOH solution. Upon removal of the applied potential, the film reverted to a state that was nearly identical to the one it had before polarization.Peer reviewed: YesNRC publication: Ye

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