Room-temperature ionic liquids (RTILs) are promising candidates for a broad range of "green" applications, for which their interaction with solid surfaces plays a crucial role. In this high-energy x-ray reflectivity study, the temperature-dependent structures of three ionic liquids with the tris(pentafluoroethyl)trifluorophosphate anion in contact with a charged sapphire substrate were investigated with submolecular resolution. All three RTILs show strong interfacial layering, starting with a cation layer at the substrate and decaying exponentially into the bulk liquid. The observed decay length and layering period point to an interfacial ordering mechanism, akin to the charge inversion effect, which is suggested to originate from strong correlations between the unscreened ions. The observed layering is expected to be a generic feature of RTILs at charged interfaces.

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The near-surface ion distribution at the solid-liquid interface during the Hydrogen Oxidation Reaction (HOR)/Hydrogen Evolution Reaction (HER) on a rotating platinum disc electrode is demonstrated in this work. The relation between reaction rate, mass transport and the resulting surface pH-value is used to theoretically predict cyclic voltammetry behaviour using only thermodynamic and diffusion data obtained from the literature, which were confirmed by experimental measurements. The effect of buffer addition on the current signal, the surface pH and the ion distribution is quantitatively described by analytical solutions and the fragility of the surface pH during reactions that form or consume H(+) in near-neutral unbuffered solutions or poorly buffered media is highlighted. While the ideal conditions utilized in this fundamental study cannot be directly applied to real scenarios, they do provide a basic understanding of the surface pH concept for more complex heterogeneous reactions.

A key parameter that controls the formation of a local galvanic element during the deadhesion of paint from base metals is the potential gradient between a defect in the paint and the intact metal oxide/polymer interface. The suitable development of zinc coatings allows for control of the potential at the intact interface and thus improvement of the delamination behavior. However, no systematic in-depth study on the origin and meaning of electrode potentials at polymer/metal interfaces or even bare metal surfaces has been presented yet, although in many recent publications Volta potential differences between inclusions and matrix measured on the surfaces of alloys are often interpreted as providing information on the galvanic activity during corrosion. It is the focus of this paper to present a detailed analysis of the origin of the potentials measured on the different materials and to point out what conclusion can be drawn from their values. Special focus is given to the technologically important system Zn-Mg.Zinc-magnesium coatings on a steel sheet perform extremely well in industrial corrosion tests in the painted as well as in the unpainted state and have therefore attracted much attention. 1 While it is reported that protective surface layers cause a reduced anodic dissolution of the coating and enhanced cathodic protection of the steel, 2-4 the high stability in the painted state indicates a greatly reduced rate of cathodic delamination. As we can show, on the intermetallic MgZn 2 , one of the main phases in zinc-magnesium coatings, cathodic delamination is totally inhibited due to a negative electrode potential of the metal oxide/polymer interface. 5 During cathodic delamination, a galvanic element forms between a defect in the polymer ͑local anode͒ and the defect border ͑local cathode͒. As a result, oxygen reduction takes place at the intact metal oxide/polymer interface next to the defect, leading to the destruction of the interface and the deadhesion of the polymer. [6][7][8][9][10][11] Cathodic delamination is the fastest mechanism causing the destruction of the metal oxide/polymer interface. As a consequence, it is essential to suppress especially this delamination mechanism in order to obtain highly stable interfaces. A key parameter that controls the formation of the local galvanic element at the delamination front is the potential gradient between the defect and the intact metal oxide/polymer interface, as it constitutes the driving force for the galvanic coupling ͑see, e.g., Ref. 11͒. Because the corrosion potential of the defect is fixed, the electrode potential of the intact metal oxide/polymer interface determines the gradient and is therefore of utmost relevance. If the oxide can be adequately adjusted in such a way that the electrode potential of the intact interface equals that of the corroding defect, it is straightforward to assume that this results in a significant and system-inherent inhibition of delamination.Such an approach requires knowledge of the factors that determine the electrod...

Raspberry-shaped redox-responsive capsules for storing corrosion inhibitors are introduced, targeted to solve the drawbacks of conducting-polymer-based coating systems for corrosion protection. These capsules synthesized via the miniemulsion technique have a remarkable release property upon reduction (onset of corrosion) and cease release upon reoxidation (passivation of the defect). The self-healing capability is demonstrated by application of these capsules as part of a composite coating on zinc.

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Redox-responsive nanocapsules consisting of conductive polyaniline and polypyrrole shells were successfully synthesized by using the interface of miniemulsion droplets as a template for oxidative polymerizations. The redox properties of the capsules were investigated by optical spectroscopies, electron microscopy, and cyclic voltammetry. Self-healing (SH) chemicals such as diglycidyl ether or dicarboxylic acid terminated polydimethylsiloxane (PDMS-DE or PDMS-DC) were encapsulated into the nanocapsules during the miniemulsion process and their redox-responsive release was monitored by (1)H NMR spectroscopy. The polyaniline capsules exhibited delayed release under oxidation and rapid release under reduction, which make them promising candidates for anticorrosion applications.

We compared the electrical properties of selfassembled monolayers (SAMs) formed on template-stripped Au from two homologous series of five different oligo-(phenylene)s bearing alkane thiol tails. The terminal phenyl ring is substituted by a 4-pyridyl ring in one series, thus the two differ only by the substitution of C−H for N. We formed tunneling junctions using the liquid metal eutectic Ga−In (EGaIn) as a nondamaging, conformal top contact that is insensitive to functional groups and measured the currentdensity, J, tunneling decay constants, β, and transition voltages, V trans . Conductance measurements alone did not sufficiently differentiate the two series of molecules. The length dependences of the two series of SAMs produced values of β of 0.44 and 0.42 Å −1 for pyridyl-and phenyl-terminated SAMs, respectively, which lie between the expected values for alkanethiolates and oligo(phenylene)s. The values of V trans were ∼0.3 V larger for the phenylterminated SAMs than for the pyridyl-terminated SAMs. A comparison of the values of J to highest occupied molecular orbital (HOMO) levels determined by density functional theory (DFT) calculations revealed an odd−even effect for the phenylterminated SAMs but not the pyridyl-terminated SAMs. Plots of V trans versus the measured shift in work function, measured with a Kelvin probe, reveal a roughly linear trend. Plots of the difference between HOMO and Fermi energies reveal a strong linear trend with two distinct series that clearly differentiate the two series of SAMs, even between SAMs with nearly identical HOMO levels, but only when the dipole-induced shift in vacuum level is considered. The influence of the electronic properties of the SAMs is clearly evident in the conductance data and highlights the importance of molecular dipoles in tunneling junctions comprising SAMs. Taken together, the data show that tunneling junctions incorporating EGaIn as a top contact are sensitive enough to differentiate SAMs that differ by the substitution of a single atom.