Parallel and perpendicular cascades in solar wind turbulence

MHD-scale fluctuations in the velocity, magnetic, and density fields of the solar wind are routinely observed. The evolution of these fluctuations, as they are transported radially outwards by the solar wind, is believed to involve both wave and turbulence processes. The presence of an average magnetic field has important implications for the anisotropy of the fluctuations and the nature of the turbulent wavenumber cascades in the directions parallel and perpendicular to this field. In particular, if the ratio of the rms magnetic fluctuation strength to the mean field is small, then the parallel wavenumber cascade is expected to be weak and there are difficulties in obtaining a cascade in frequency. The latter has been invoked in order to explain the heating of solar wind fluctuations (above adiabatic levels) via energy transfer to scales where ion-cyclotron damping can occur. Following a brief review of classical hydrodynamic and magnetohydrodynamic (MHD) cascade theories, we discuss the distinct nature of parallel and perpendicular cascades and their roles in the evolution of solar wind fluctuations

E-ALD: Tailoring the Optoeletronic Properties of Metal Chalcogenides on Ag Single Crystals

Technological development in nanoelectronics and solar energy devices demands nanostructured surfaces with controlled geometries and composition. Electrochemical atomic layer deposition (E-ALD) is recognized as a valid alternative to vacuum and chemical bath depositions in terms of growth control, quality and performance of semiconducting systems, such as single 2D semiconductors and multilayered materials. This chapter is specific to the E-ALD of metal chalcogenides on Ag single crystals and highlights the electrochemistry for the layer-by-layer deposition of thin films through surface limited reactions (SLRs). Also discussed herein is the theoretical framework of the under potential deposition (UPD), whose thermodynamic treatment open questions to the correct interpretation of the experimental data. Careful design of the E-ALD process allows fine control over both thickness and composition of the deposited layers, thus tailoring the optoelectronic properties of semiconductor compounds. Specifically, the possibility to tune the band gap by varying either the number of deposition cycles or the growth sequence of ternary compounds paves the way toward the formation of advanced photovoltaic materials

Corrosion Resistance Test of Electroplated Metals using Fast Electrochemical Non-Destructive Analysis

Corrosion testing is a very important step in quality control for metal industrial processes. Especially for electroplated goods, corrosion resistance is a primary indicator of surface quality. International Standard Organization has established several standards that use Electrochemical Impedance Spectroscopy (EIS), alone or combined with other electrochemical techniques, to determine corrosion resistance of metal surfaces such ISO 16773 for testing coated and uncoated metallic specimens and ISO 17463 specially designed for organic-coated metal surfaces. EIS is a versatile procedure for the accelerated evaluation of the anti-corrosion performance of coatings: unlike other standard procedures is generally a non-destructive method. EIS works applying an electrical sinusoidal perturbation with a fixed frequency and measuring electrical impedance Z of the sample. Measuring impedance at different frequencies and analysing the data it is possible to postulate the structure of an equivalent circuit and extract corrosion resistance data. This approach is commonly used for high-impedance coatings, in this study we will explore EIS as well as the OCP measurement, the corrosion current and other techniques to find the best option for low-impedance metallic coatings analysis. The objective of this study is to develop a method to determine corrosion resistance for electroplated goods that can give results as reliable as other more diffuse and traditional destructive corrosion testing techniques (such as corrosion tests in artificial atmosphere ISO 9227 and ISO 17228) with a non-destructive process and in a fair less amount of time

Stimulus-Responsive Au@(MeO₂MA_<i>x</i>-<i>co</i>-OEGMA_<i>y</i>) Nanoparticles Stabilized by Non-DLVO Interactions: Implications of Ionic Strength and Copolymer (<i>x</i>:<i>y</i>) Fraction on Aggregation Kinetics

Functionalized nanoparticles can assist in stabilizing fluid–fluid interfaces; however, developing and applying the appropriate surface modification presents a challenge because successful application of these nanomaterials for biotechnological, food processing, and environmental applications requires their long-term stability in elevated ionic strength media. This work studies stimulus responsive polymeric materials based on random copolymers of di­(ethylene glycol) methyl ether methacrylate (<i>x </i>= MeO₂MA) and oligo­(ethylene glycol) methyl ether methacrylate (<i>y</i>= OEGMA) which, when grafted to gold nanoparticles, show significant, tunable, colloidal stability. The nanoparticles Au@(MeO₂MA_<i>x</i>-<i>co</i>-OEGMA_<i>y</i>) display tunable, reversible aggregation that is highly dependent on the (<i>x</i>:<i>y</i>) ratio and ionic strength. Effects of these parameters on the initial rate constant of aggregation (<i>k</i>_<i>11</i>) are studied by time-resolved dynamic light scattering (TR-DLS) experiments. At the same nanoparticle concentration, a strong sensitivity to salt concentration is observed. Over less than 300 mM increase in NaCl concentration, we observed a two-order of magnitude increase in aggregation rate constants, 4.2 × 10^–20 < <i>k</i>_<i>11</i> < 1.8 × 10^–18 m³s^–1. Additionally, for the same gold nanoparticles, a higher fraction of OEGMA requires a higher salt concentration to induce aggregation. A linear relationship between the critical NaCl coagulation concentration (CCC) and the copolymer composition is observed. Analysis of the experimental data with an extended Derjaguin–Landau–Verwey–Overbeek (xDLVO) theory that includes hydration and osmotic forces is used to explain the stability of these systems. We find the hydration pressure, 2.4 < <i>P</i>_h,0 < 7.2 MPa, scales linearly both with the osmotic pressure and the OEGMA monomer concentration (5 <<i> y</i> < 20%). Specific knowledge of <i>P</i>_h,0(<i>y, C</i>_NaCl) enables design of both aggregation kinetics and stability as a function of the copolymer ratio and external stimuli

Electroplating for Decorative Applications: Recent Trends in Research and Development

Electroplating processes are widely employed in industrial environments for a large variety of metallic coatings, ranging from technological to decorative applications. Even if the galvanic electrodeposition is certainly a mature technology, new concepts, novel applications, environmental legislation and the new material requirements for next-generation devices make the scientific research in this field still very active. This review focuses mostly at the decorative and wearable applications, and aims to create a bridge between the past knowledge and the future direction that this process, i.e., electrodeposition, is taking. Both the theoretical fundamentals as well as some of the most widespread practical applications&mdash;limited to metallic and alloy coatings&mdash;are explored. As an integral part of the industrial process, we take a look at the main techniques thought which the quality control of deposits and surfaces is carried out. Finally, global industrial performance and research directions towards sustainable solutions are highlighted

Corrosion Resistance Test of Electroplated Gold and Palladium Using Fast Electrochemical Analysis

Noble metal coatings are commonly employed to improve corrosion resistance of metals in the electronic and jewellery industry. The corrosion resistance of electroplated goods is currently determinate with long, destructive and almost subjective interpretation corrosion tests in artificial atmosphere. In this study we present the application of electrochemical analysis to obtain fast and numerical information of the antiaging coating. We performed open circuit potential (OCP) and corrosion current measurement; we employed also the electrochemical impedance spectroscopy (EIS), commonly applied to organic or passivated metal with high-impedance, to find the best option for noble low-impedance coating analysis. For comparison, traditional standardized tests (damp heat ISO 17228, salt spray ISO 9227 and sulphur dioxide ISO 4524) were also performed

Corrosion Resistance Test of Electroplated Gold and Palladium Using Fast Electrochemical Analysis

Noble metal coatings are commonly employed to improve corrosion resistance of metals in the electronic and jewellery industry. The corrosion resistance of electroplated goods is currently determinate with long, destructive and almost subjective interpretation corrosion tests in artificial atmosphere. In this study we present the application of electrochemical analysis to obtain fast and numerical information of the antiaging coating. We performed open circuit potential (OCP) and corrosion current measurement; we employed also the electrochemical impedance spectroscopy (EIS), commonly applied to organic or passivated metal with high-impedance, to find the best option for noble low-impedance coating analysis. For comparison, traditional standardized tests (damp heat ISO 17228, salt spray ISO 9227 and sulphur dioxide ISO 4524) were also performed

Engineering Adhesion to Thermoresponsive Substrates: Effect of Polymer Composition on Liquid–Liquid–Solid Wetting

Adhesion control in liquid–liquid–solid systems represents a challenge for applications ranging from self-cleaning to biocompatibility of engineered materials. By using responsive polymer chemistry and molecular self-assembly, adhesion at solid/liquid interfaces can be achieved and modulated by external stimuli. Here, we utilize thermosensitive polymeric materials based on random copolymers of di­(ethylene glycol) methyl ether methacrylate (<i>x</i> = MEO₂MA) and oligo­(ethylene glycol) methyl ether methacrylate (<i>y</i> = OEGMA), that is, P­(MEO₂MA_<i>x</i>-<i>co</i>-OEGMA_<i>y</i>), to investigate the role of hydrophobicity on the phenomenon of adhesion. The copolymer ratio (<i>x</i>/<i>y</i>) dictates macromolecular changes enabling control of the hydrophilic-to-lipophilic balance (HBL) of the polymer brushes through external triggers such as ionic strength and temperature. We discuss the HBL of the thermobrushes in terms of the surface energy of the substrate by measuring the contact angle at water–decane–P­(MEO₂MA_<i>x</i>-<i>co</i>-OEGMA_<i>y</i>) brush contact line as a function of polymer composition and temperature. Solid supported polyelectrolyte layers grafted with P­(MEO₂MA_<i>x</i>-<i>co</i>-OEGMA_<i>y</i>) display a transition in the wettability that is related to the lower critical solution temperature of the polymer brushes. Using experimental observation of the hydrophilic to hydrophobic transition by the contact angle, we extract the underlying energetics associated with liquid–liquid–solid adhesion as a function of the copolymer ratio. The change in cellular attachment on P­(MEO₂MA_<i>x</i>-<i>co</i>-OEGMA_<i>y</i>) substrates of variable (<i>x</i>/<i>y</i>) composition demonstrates the subtle role of compositional tuning on the ability to control liquid–liquid–solid adhesion in biological applications