Ashokanand Vimalanandan

Redox Responsive Release of Hydrophobic Self-Healing Agents from Polyaniline Capsules

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.

Redox‐Responsive Self‐Healing for Corrosion Protection

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.

Regenerative Nano‐Hybrid Coating Tailored for Autonomous Corrosion Protection

A novel bilayer coating system for autonomous corrosion-triggered self-healing is demonstrated. The storage of the encapsulated monomer and the catalyst is separated in two different layers. The encapsulated catalyst is stored inside a metallic coating, which ensures its activity even for an extended exposure time. The release from the capsules is triggered by corrosion and the correlated pH increase.

Existence of a Lower Critical Radius for Incorporation of Silica Particles into Zinc during Electro-codeposition

Recently, it was shown that the surface modification of silica particles with -SH functional groups enables their electro-codeposition with zinc. Here, however, we report that no incorporation into Zn can be observed for such modified particles with diameters of <100 nm, while incorporation is possible for particles with diameters of 225 nm and larger. Furthermore, when silica particles are functionalized with mixtures of -SH and -Cl functional groups, which affect the interface energy at the particle/metal interface differently but have similar interfacial energies for the particle/electrolyte interface, it is found that, for successful incorporation of the particles, a minimum amount of -SH functional groups is needed. An explanation for these observations has been derived based on energetic considerations regarding the interfaces involved in the process.

Fundamentals of Electrochemistry, Corrosion and Corrosion Protection

This chapter introduces the basics of electrochemistry, with a focus on electron transfer reactions. We will show that the electrode potential formed when a metal is immersed in a solution is most of the time not an equilibrium potential, but a mixed potential in a stationary state. This mixed potential formation is the basis of corrosion of metals in aqueous solutions. Organic coatings are introduced as protecting agents, and several types of coatings are discussed: classical passive coatings, and active coatings as modern developments. Three electrochemical techniques, which are commonly used to asses the protecting properties of coatings, are shortly introduced as well: linear polarisation measurements, electrochemical impedance spectroscopy, and scanning Kelvin probe measurements.

Fabrication of Robust Reference Tips and Reference Electrodes for Kelvin Probe Applications in Changing Atmospheres

The scanning Kelvin probe (SKP) is a versatile method for the measurement of the Volta potential difference between a sample and the SKP-tip (ΔψsampleSKP-tip). Based on suitable calibration, this technique is highly suited for the application in corrosion science due to its ability to serve as a very sensitive noncontact and nondestructive method for determining the electrode potential, even at buried interfaces beneath coatings or on surfaces covered by ultrathin electrolyte layers, which are not accessible by standard reference electrodes. However, the potential of the reference (i.e., the SKP-tip) will be influenced by variations of the surrounding atmosphere, resulting in errors of the electrode potential referred to the sample. The objective of this work is to provide a stable SKP-tip which can be used in different or changing atmosphere, e.g., within a wide range of relative humidity (approximately 0-99%-rh) or varying O2 partial pressure, without showing a change of its potential (note that the work functions measured in non-UHV atmospheres are electrochemical in nature [Hausbrand et al. J. Electrochem. Soc. 2008, 155 (7), C369-C379], and hence in the following we will refer to the potential of the SKP-tip instead of its work function). In that regard, the SKP-tip is in a first approach modified with self-assembled monolayers (SAMs) in order to create a hydrophobic barrier between the metallic surface and the surrounding atmosphere. The changes in potential upon varying relative humidity (ΔErh) of different bare metallic substrates are quantified, and it is shown that these potential differences cannot be minimized by SAMs. On the contrary, the ΔErh increases for every examined material system modified with SAMs. The major explanation for this observation is the dipole layer at the interface metal|SAM, causing an interfacial adsorption of water molecules even in a preferred orientation of their dipole moments, which leads to a changed work function and consequently to the correlated electrode potential. However, thin paraffin coatings were found to lead to a strongly reduced ΔErh, finally validated with novel robust Ag/Ag+ reference electrodes. It is also shown that nickel as SKP-tip material is seemingly more stable in varying atmospheric conditions compared to widely used Ni/Cr, stainless steel, or gold as SKP-tip material.

Electro-codeposition of modified silica colloids and copper

Abstract Copper-silica composite coatings were prepared by electro-codeposition on stainless steel substrates. The influence of functionalization and surface charge of SiO2 particles on the electrodeposition of Cu-SiO2 nanocomposite coating was studied. SiO2-SH particles were embedded inside the metal matrix whereas particles with other surface termination did not incorporate inside the metal matrix. Moreover, cysteamine addition to the electrolyte containing bare SiO2 particles induced embedding of particles into the metal matrix. The diameter-dependence of incorporation of -SH functionalized SiO2 particles as well as the role of the density of the effective functional group (-SH) for successful incorporation into Cu have been investigated. Infrared (IR) and X-ray photoelecotron (XPS) spectroscopy were used to observe the interaction of Cu2+ ions with thiol groups, showing a Cu2+ binding. The incorporated particles were found to increase the microhardness of the coating.