1,720,995 research outputs found
Well-Controlled Organic Monolayers as Model Inhibitors for Dealloying Corrosion of Noble Metal Alloys
No full textMaterials degradation due to corrosion is one of the most critical problems on our way to a more sustainable society because of the extensive use of alloys in sensors, electronic appliances, fuel storages and supplies, chips and micro - nano devices. Understanding the fundamental microscopic processes in corrosion initiation and development at the atomic level is essential to improve corrosion protection and resistance by inhibitors. Despite the fact that a substantial number of reports on corrosion testing are available, only a few of them aspired to understand the basic processes driving materials degradation on an atomic or molecular level. Many researches have been devoted to find possible organic inhibitors to protect metallic alloys. An interesting type of alloy corrosion, localized dealloying, takes place in alloy surfaces protected by self-assembled monolayers (SAMs) of organic inhibitors such as alkanethiols and selenols but, the mechanism behind the localized dealloying initiation still remains unexplored. Therefore, dealloying initiation at the nanoscale can be addressed by controlling the spatial distribution and molecular organization of SAMs at nano and micro length scales. The aim of this PhD thesis is to gain insights into localized dealloying initiation of noble metal alloys, mainly Cu3Au, as a model system by using well-controlled alkanethiol SAMs. Similarly, the nanoscale inhibitor stability and corrosion efficiency in pure Cu and Cu-based alloys was also investigated.
Initially, different chain-length alkanethiols were tested on a reference surface, ultraflat gold (UFG), by using a multistep approach of microcontact printing (µCP) combined with subsequent backfilling. The molecular organization of single and double printed (2-µCP) followed by further backfilling to produce complex alkanethiol SAMs was characterized by atomic force microscope (AFM) at the nanoscale. By using double printing, both alkanethiol forms coexist as compact SAMs with well-defined thickness. Microcontact printing and further backfilling with the same molecule resulted in well-delimited nanometer-thick domain boundaries of micrometer-range lateral dimension in between patterned and backfilled areas. This finding provides an opportunity to explore localized dealloying at the nanoscale level in the presence of well-defined complex alkanethiol inhibitor layers. Microcontact printing and subsequent backfilling of different chain-length alkanethiol creates artificial heterogeneous molecular interfaces in well-controlled way which trigger localized dealloying corrosion at the artificially created defects such as the patch backfilled boundaries. Such heterogeneous inhibitor assemblies strongly depend on nanoscale geometrical and chemical features of the metal-film interface and are in turn ultimately important for surface processes such as corrosion and corrosion inhibition. Electrochemical dealloying in the presence of such complex alkanethiol inhibitor revealed that localized dealloying initiation starts at the boundary region between two differently approached molecules, as well as from the junction between two print patches. Besides this, the Cu dissolution also initiates from the SAM defect areas on regions with a high density of atomic terraces, developing either large circular or more delimited star-shaped dealloying pits. Thus, localized dealloying initiation is strongly dependent on the alloy surface morphology but also the stability of the applied inhibitor molecule. This work uses model systems to reach better insights at the atomic or molecular level of localized corrosion initiation process.
In addition, SAMs of mercapto-based imidazole derivatives were used as model corrosion inhibitors for Cu and Cu-Zn alloys. Several selected imidazole derivatives were chosen to gain understanding of the monolayer stability at the molecular and nanoscale by in-situ force spectroscopy AFM (FS-AFM) and its influence on macroscale corrosion inhibition. In this work, two imidazole-based inhibitors were studied, commonly being used for Cu surface protection. The molecular stability and intermolecular forces of SAMs consisting of imidazole derivatives, namely, 5-methoxy-2-mercapto-benzimidazole (SH-BimH-5OMe) and 5-amino-2-mercapto-benzimidazole (SH-BimH-5NH2) on Cu surfaces were characterized experimentally by AFM, and theoretically by density functional theory (DFT) in collaboration. The inhibitor-covered Cu surfaces were characterized by AFM imaging and by tip-sample force measurements using Quantitative Imaging (QI) mode AFM. For a SH-BiMH-5NH2 molecular layers, molecular fishing by the AFM tip frequently occurred with about 20% of total events, displaying a ‘fishing’ force magnitude representative of intermolecular attractions rather than a surface bond strength. For SH-BimH-5OMe molecules, no molecular fishing events were observed, indicating more stable layers in line with its better Cu corrosion efficiency. Both, computational modeling and electrochemical corrosion measurements also proved that the SH-BiMH-5OMe-covered Cu surface is more protective. This study helped to gain knowledge on noble metal alloy corrosion, which contributes towards an understanding of more complex and more reactive alloys mostly found in real-world applications
Well-Controlled Organic Monolayers as Model Inhibitors for Dealloying Corrosion of Noble Metal Alloys
No full textMaterials degradation due to corrosion is one of the most critical problems on our way to a more sustainable society because of the extensive use of alloys in sensors, electronic appliances, fuel storages and supplies, chips and micro - nano devices. Understanding the fundamental microscopic processes in corrosion initiation and development at the atomic level is essential to improve corrosion protection and resistance by inhibitors. Despite the fact that a substantial number of reports on corrosion testing are available, only a few of them aspired to understand the basic processes driving materials degradation on an atomic or molecular level. Many researches have been devoted to find possible organic inhibitors to protect metallic alloys. An interesting type of alloy corrosion, localized dealloying, takes place in alloy surfaces protected by self-assembled monolayers (SAMs) of organic inhibitors such as alkanethiols and selenols but, the mechanism behind the localized dealloying initiation still remains unexplored. Therefore, dealloying initiation at the nanoscale can be addressed by controlling the spatial distribution and molecular organization of SAMs at nano and micro length scales. The aim of this PhD thesis is to gain insights into localized dealloying initiation of noble metal alloys, mainly Cu3Au, as a model system by using well-controlled alkanethiol SAMs. Similarly, the nanoscale inhibitor stability and corrosion efficiency in pure Cu and Cu-based alloys was also investigated.
Initially, different chain-length alkanethiols were tested on a reference surface, ultraflat gold (UFG), by using a multistep approach of microcontact printing (µCP) combined with subsequent backfilling. The molecular organization of single and double printed (2-µCP) followed by further backfilling to produce complex alkanethiol SAMs was characterized by atomic force microscope (AFM) at the nanoscale. By using double printing, both alkanethiol forms coexist as compact SAMs with well-defined thickness. Microcontact printing and further backfilling with the same molecule resulted in well-delimited nanometer-thick domain boundaries of micrometer-range lateral dimension in between patterned and backfilled areas. This finding provides an opportunity to explore localized dealloying at the nanoscale level in the presence of well-defined complex alkanethiol inhibitor layers. Microcontact printing and subsequent backfilling of different chain-length alkanethiol creates artificial heterogeneous molecular interfaces in well-controlled way which trigger localized dealloying corrosion at the artificially created defects such as the patch backfilled boundaries. Such heterogeneous inhibitor assemblies strongly depend on nanoscale geometrical and chemical features of the metal-film interface and are in turn ultimately important for surface processes such as corrosion and corrosion inhibition. Electrochemical dealloying in the presence of such complex alkanethiol inhibitor revealed that localized dealloying initiation starts at the boundary region between two differently approached molecules, as well as from the junction between two print patches. Besides this, the Cu dissolution also initiates from the SAM defect areas on regions with a high density of atomic terraces, developing either large circular or more delimited star-shaped dealloying pits. Thus, localized dealloying initiation is strongly dependent on the alloy surface morphology but also the stability of the applied inhibitor molecule. This work uses model systems to reach better insights at the atomic or molecular level of localized corrosion initiation process.
In addition, SAMs of mercapto-based imidazole derivatives were used as model corrosion inhibitors for Cu and Cu-Zn alloys. Several selected imidazole derivatives were chosen to gain understanding of the monolayer stability at the molecular and nanoscale by in-situ force spectroscopy AFM (FS-AFM) and its influence on macroscale corrosion inhibition. In this work, two imidazole-based inhibitors were studied, commonly being used for Cu surface protection. The molecular stability and intermolecular forces of SAMs consisting of imidazole derivatives, namely, 5-methoxy-2-mercapto-benzimidazole (SH-BimH-5OMe) and 5-amino-2-mercapto-benzimidazole (SH-BimH-5NH2) on Cu surfaces were characterized experimentally by AFM, and theoretically by density functional theory (DFT) in collaboration. The inhibitor-covered Cu surfaces were characterized by AFM imaging and by tip-sample force measurements using Quantitative Imaging (QI) mode AFM. For a SH-BiMH-5NH2 molecular layers, molecular fishing by the AFM tip frequently occurred with about 20% of total events, displaying a ‘fishing’ force magnitude representative of intermolecular attractions rather than a surface bond strength. For SH-BimH-5OMe molecules, no molecular fishing events were observed, indicating more stable layers in line with its better Cu corrosion efficiency. Both, computational modeling and electrochemical corrosion measurements also proved that the SH-BiMH-5OMe-covered Cu surface is more protective. This study helped to gain knowledge on noble metal alloy corrosion, which contributes towards an understanding of more complex and more reactive alloys mostly found in real-world applications
Solvent-Assisted Lipid Bilayer Formation on Au Surfaces: Effect of Lipid Concentration on Solid-Supported Membrane Formation
No full textSolvent-assisted lipid bilayer (SALB) formation is emerged as a versatile approach in forming supported lipid membranes (SLBs) on metal surfaces, interesting platforms for transducing a biological signal to an electrical readout where vesicle rupture is not straightforward. Herein, the effect of the lipid concentration in the organic solvent, a key parameter controlling SALB, is addressed in the low and high concentration limits of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine lipid on a Au surface. Quartz crystal microbalance with dissipation (QCM-D) responses are correlated with atomic force microscopy (AFM) topographic and nanomechanical measurements. Upon SALB completion at both concentrations, QCM-D and AFM topographical characterization suggest the formation of thin, although incomplete, lipid layers at the Au–liquid interface, with frequency and dissipation plateau values departing from well-established homogeneous SLB responses. Nanomechanical analysis reveals the presence of mostly monolayers at low concentration due to lack of lipid material, while at high concentration excess of lipid material leads to the coexistence of diverse structures. Their formation stems from the SALB formation mechanism, based on lyotropic transformations upon solvent exchange, which differs from customarily vesicle rupture. Such mechanism leads to peculiar two-step features in approach force curves on SLBs pointing toward a decoupling in bilayer leaflets when supported.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Quartz Crystal Microbalance With Dissipation Monitoring: A Versatile Tool to Monitor Phase Transitions in Biomimetic Membranes
No full textSolid-supported lipid membranes are popular models that connect biological and artificial materials used in bio-technological applications. Controlling the lipid organization and the related functions of these model systems entails understanding and characterizing their phase behavior. Quartz crystal microbalance with dissipation monitoring (QCM-D) is an acoustic-based surface-sensitive technique which is widely used in bio-interfacial science of solid-supported lipid membranes. Its sensitivity to mass and energy dissipation changes at the solid-lipid layer-liquid interface allows the detection of phase transformations of solid-supported membrane geometries. In this perspective, we highlight this valuable feature and its related methodology, review current advances and briefly discuss future perspectives. Furthermore, a specific example is also provided on the ability of QCM-D to detect changes in lipid organization of cholesterol containing solid-supported lipid vesicle layers (SVLs) upon the addition of aspirin.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
In Operando Atomic Force Microscopy Imaging of Electrochemical Interfaces: A Short Perspective
No full textElectrochemical interfaces are at the core of many important current applications, from corrosion and biophysics to electrocatalytic and battery interfaces. Further understanding in the processes taking place at these interfaces is often linked to better observation techniques. In situ or in operando imaging and characterization of the electrochemical interface helps improve our understanding of structural sequences and kinetics of complex processes. Atomic force microscopy (AFM) offers a unique combination to monitor surface morphology and mechanical properties at micro- and nanoscale surfaces and solid–electrolyte interfaces. Two examples are given where the application of AFM during electrochemical processes is clearly useful. Organic inhibitors and their behavior play an important role in corrosion mitigation and the influence of thiol monolayers on dealloying is reported: Zinc films find application for coatings or Zn batteries and an in situ electrodeposition study is shortly described. With the ongoing improvement of computational simulations, the broadening of spatiotemporal scales possible with AFM imaging and its combination with mechanical information points in a prospective future for in operando AFM.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Simplistic correlations between molecular electronic properties and inhibition efficiencies: Do they really exist?
Full text linkThe often used simplistic correlations between molecular electronic parameters and experimentally determined corrosion inhibition efficiencies are critically evaluated for a set of 24 heterocyclic organic compounds, tested as corrosion inhibitors for copper in 3 wt.% NaCl aqueous solution. Twelve different molecular electronic descriptors—such as ionization potential, electron affinity, HOMO–LUMO gap, dipole moment—are tested and it is shown that none of them displays any noticeable correlation with the inhibition efficiency. Our results, therefore, cast serious doubt on reported correlations between such parameters and inhibition efficiency, obtained for only a few inhibitors, which are abundant in the literature. We also discuss some pros and cons of inhibition efficiency as a metric for evaluating the performance of corrosion inhibitors, and introduce a new metric termed inhibition power that uses the universal logarithmic scale and dimensionless decibel (dB) units.Team Peyman TaheriTeam Arjan Mo
Study Of Mercaptobenzimidazoles As Inhibitors For Copper Corrosion: Down to the Molecular Scale
No full textThe initiation of corrosion can be triggered by defects in the adsorbed layer of organic inhibitors. A detailed knowledge of the intermolecular forces between the inhibitor molecules and the interfacial bonding will be decisive to unravel the mechanisms driving the corrosion initiation. In this work, adsorbed organic layers of 2-mercapto-5-methoxybenzimidazole (SH-BimH-5OMe) and 5-amino-2-mercaptobenzimidazole (SH-BimH-5NH2) were compared regarding their performance mitigating copper corrosion. Atomic force microscopy was used to address the stability and intermolecular forces of the self-assembled monolayers, using imaging and force measurement modes. For a film formed by amino-derivative molecules, a gold-coated tip frequently picked up individual molecules (molecular fishing) in force-distance measurements. For layers of the methoxy-derivative, no fishing events were observed, pointing to a constant functional layer. X-ray photoelectron spectroscopy revealed that SH-BimH-5OMe molecules form a stronger bond with the surface and more stable SAM layers on Cu surfaces as compared to SH-BimH-5NH2 molecules. Results of computational density functional theory modeling and electrochemical corrosion tests are in line with the microscopy and spectroscopy results. In particular, with aid of computational modeling the less ordered structure of the SH-BimH-5NH2 monolayer is attributed to dual bonding ability of SH-BimH-5NH2 that can adsorb with either S or NH2 groups.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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