We propose a potential‐pulse‐assisted method for the formation of highly compact thiol self‐assembled monolayers (SAMs), ensuring fully covered surfaces within minutes. By pulsing between potentials that are more positive and more negative with respect to the potential of zero charge, kinetics of SAM formation is substantially enhanced. The formation of the SAM is followed by using real‐time impedance measurements by superimposing the applied potential‐pulse profile with a high‐frequency AC signal that allows for calculation of the interfacial capacitance and provides information about the compactness of the formed layers. A systematic study of the influence of the pulse potential intensity, the pulse duration, and the nature of the thiol derivative on the potential‐pulse‐assisted SAM formation is performed. We show that compact thiol monolayers are obtained much faster with the suggested technique, as compared to SAM formation performed at the open‐circuit potential or by applying a constant potential.
Control over the properties of ultrathin films plays a crucial role in many fields of science and technology. Although nondestructive optical and electrical methods have multiple advantages for local surface characterization, their applicability is very limited if the surface is in contact with an electrolyte solution. Local electrochemical methods, e.g., scanning electrochemical microscopy (SECM), cannot be used as a robust alternative yet because their methodological aspects are not sufficiently developed with respect to these systems. The recently proposed scanning electrochemical impedance microscopy (SEIM) can efficiently elucidate many key properties of the solid/liquid interface such as charge transfer resistance or interfacial capacitance. However, many fundamental aspects related to SEIM application still remain unclear. In this work, a methodology for the interpretation of SEIM data of "charge blocking systems" has been elaborated with the help of finite element simulations in combination with experimental results. As a proof of concept, the local film thickness has been visualized using model systems at various tip-to-sample separations. Namely, anodized aluminum oxide (Al2O3, 2-20 nm) and self-assembled monolayers based on 11-mercapto-1-undecanol and 16-mercapto-1-hexadecanethiol (2.1 and 2.9 nm, respectively) were used as model systems.
This work is aimed to investigate the metal content (i.e., Cu, Pb, Cd y Zn) present in Mexican spirituous beverages which include: Tequila, Raicilla, Sotol and Mezcal by using Differential Pulse Polarography (DPP). Metal content depends on the type of beverage, geographic region of origin, and aging stage. Noteworthy is metal removal, specifically copper, during the aging process of tequila, suggesting a copper capture by the oak wooden aging barrel. Metal content in aged beverages can be an alternative method to estimate both aging time and sneaky aged tequilas. Further, the results presented in this paper may provide a guide to establish metal regulations to improve quality control of spirituous Mexican beverages.
The modification of graphite electrode surfaces with different hardness using hexane/CTAB-CTAmodified-butanol/water microemulsion forming system with inverse micelles (W/O) is presented. CTAB is modified by exchanging bromide ions of the surfactant with ferrocyanide ions in a salt solution. Carbon electrodes are modified by immersing them into a W/O microemulsion, followed by a rinsing step with pure water, and a potential cycling in a ferrocyanide solution. After this treatment, electrodes display two redox peaks, characteristic of strongly adsorbed species. The amount of adsorbed material at the electrode surface is greater for soft graphite electrodes than for hard ones. FTIR spectra of carbon electrodes before and after modification not show signal of C-C bonds and the increase of C-N signal from ferrocyanide ions attached to the surfactant. These results support the formation of a new bond between the surfactants tail and the carbon surface.
The formation of a localized differential aeration cell on metals, susceptible to both anodic and cathodic corrosion, is a serious threat because of multiple degradation processes commencing with the passivation layer destruction. By using local electrochemical and X‐ray dispersive techniques, it has been demonstrated that the differential aeration cell formed on high brass (α‐brass, Cu65‐Zn35) in the presence of 1H‐benzotriazole or 5‐methyl‐1H‐benzotriazole plays both corrosion‐inhibiting and accelerating roles, depending on the inhibitor exposure time. Alternating‐current scanning electrochemical microscopy was used to image local electrochemical activity, whereas energy‐dispersive X‐ray spectroscopy provided evidence for the mechanism of the observed phenomena. Short‐term exposure to the inhibitor (5 min) promotes the formation of a passivation layer in the waterline region. In contrast, after prolonged exposure (45 min), a deficient passivation layer develops for both inhibitors. An excess of zinc(II)–inhibitor complexes in the passivation layer is accountable for the corrosion resistance of the region with high differential aeration. Rapid dezincification and local alkalinization facilitate the initial rapid formation of a passivation layer in the area under differential aeration to preserve its composition upon further modification.
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