Surface Modification Of Metals Research Articles

Optimizing bidentate N-heterocyclic carbene ligands for the modification of late transition metal surfaces - new insights through theory.

The functionalization of metal surfaces with N-heterocyclic carbenes (NHCs) has gained much interest in the past decade, since the modified materials are highly suitable for the development of specialized applications, for example in heterogeneous catalysis. More recently, multidentate NHC-ligands have been utilized to further improve the properties of the modified materials. However, the influence of the linker, which connects the NHC units, on the adsorption behavior of multidentate NHC-ligands has not been investigated so far. This knowledge is essential in order to access the full potential of applications. Here, we provide a thorough computational study, which compares the performance of bidentate NHC-ligands with twelve different linkers on the Cu(111), Pd(111) and Au(111) surfaces. It is shown that, on the Cu(111) and Au(111) surfaces, linkers should most importantly allow for a favorable arrangement of all NHC units, while aromatic linkers lead to stronger adsorption than aliphatic ones on Pd(111) surfaces. As a consequence, bidentate NHCs with aromatic linkers on Pd(111) surfaces tolerate larger deviations from the optimum single-NHC adsorption mode.

Surface modification of plasmonic noble metal-metal oxide core-shell nanoparticles.

A comprehensive survey on the methods for the surface modification of plasmonic noble metal–metal oxide core–shell nanoparticles is presented. The review highlights various strategies for covalent attachment and electrostatic binding of molecules and molecular ions to core–shell nanoparticles with a focus on plasmonically active silver and gold nanoparticles encapsulated by SiO2 and TiO2 shells.

The surface chemistry of metal-organic frameworks and their applications.

Modifying the outer surfaces of metal-organic frameworks (MOFs) has received considerably less attention than functionalization of the bulk, despite the range of physical and chemical properties that can be tuned by controlling MOF surface chemistry. In this Frontier article, we summarise developments over the last five years in both functionalizing and visualizing the outer surfaces of MOFs, with particular focus on their application as surface-modified nanoparticles for drug delivery and in the enhanced self-assembly of hybrid materials.

Novel bioelectrodes based on polysaccharide modified gold surfaces and electrochemically active Lactobacillus rhamnosus GG biofilms

Lactobacillus rhamnosus GG is an environmentally and human-friendly bacteria that can be found in probiotics. However, it is incapable of forming a biofilm on metal surfaces, what limits the possibility of using it in bioelectrochemical systems (BESs) as promising and green alternatives. Hence, we propose a simple and cost-effective modification of metal surface with cationic dextran derivative (DEX-G) by using the electrostatically driven self-assembly procedure resulting in the formation of a polymeric monolayer. Modification of metal electrodes was confirmed by using infrared spectroscopy (IR) and atomic force microscopy (AFM). Synthesized metal/polycation electrodes provided a bioactive environment for L. rhamnosus GG enhancing its proliferation and formation of the biofilm as confirmed by SEM imaging. Moreover, using cyclic voltammetry (CV) and chronoamperometry measurements, it was proven that metal/polycation/L. rhamnosus bioelectrodes are electrochemically active in the glucose-rich medium. The electrochemical activity of fabricated bioanodes allows to consider them for their potential use in the bioelectrochemical systems.

Dendrite-Free Li Metal Anode for Rechargeable Li-SO2 Batteries Employing Surface Modification with a NaAlCl4-2SO2 Electrolyte.

Dendritic growth of a Li metal anode during cycling is one of major issues to be addressed for practical application of Li metal rechargeable batteries. Herein, we demonstrate that surface modification of Li metal with a Na-containing SO2 electrolyte can be an effective way to prevent dendritic Li growth during cell operation. The surface-modified Li metal anode exhibited no dendritic deposits even under a high areal capacity (5 mA h cm-2) and a high current density (3 mA cm-2), whereas the unmodified anode showed typical filamentary Li deposition. The surface-modified Li metal anode also demonstrated significantly enhanced electrochemical performance, which could be attributed to the newly formed Na-containing inorganic surface layer that exhibits uniform and dense properties. Consequently, surface modification with a Na-containing SO2 inorganic electrolyte is suggested as one of the most effective ways to realize a highly stable Li metal anode with dendrite-free Li deposition for Li metal-based rechargeable batteries.

Plasma-arc surface modification of metals in a liquid medium

The method of saturation of the steel surface with carbon under the action of a plasma electric arc in a liquid is considered. The microstructure and microhardness of the hardened layer after treatment using this method were studied. It is established that during the time of plasma action of 0.1-1c the surface layer is saturated with carbon and nitrogen to the level of concentration of high-carbon steel. Microstructures and characteristics of the metal surface after plasma modification in a liquid medium were studied. The main parameters of the modified layer were determined: depth of the layer is 15-1200 μm, microhardness reaches 7.000-14.000 MPa.

Wrapping flexible metal–organic framework with organic polymers via site-specific radical polymerization from its crystal surface

In this study, we succeeded in the crystal surface modification of metal–organic framework (MOF) with an organic polymer by site-specific radical polymerization. A MOF was selected with interpenetrated structure containing a naphthalenediimide moiety with electron accepting capability. N, N-dimethylaniline, as an electron donating guest, induced electron transfer to the napthalenediimide moiety, generating radical anions on the pore and crystal surfaces, initiating radical polymerization. The resulting composite was examined in detail with XRD, TG, TEM, ICP, IR, gas adsorption, and fluorescent measurements, demonstrating that an organic polymer was generated only on the crystal surface, preserving the original porous property. In addition, higher structural stability in response to H2O was observed after polymer wrapping.

A Comparative Study on Performance Improvement of ZnO Nanotubes Based Alcohol Sensor Devices by Pd and rGO Hybridization

This paper concerns a comparative study on the improved alcohol sensing performance of ZnO nanotubes (NTs) based devices via two means: 1) by widely explored catalytic noble metal (Pd) surface modification (Type 1 device) and 2) relatively less explored technique of surface decoration by reduced graphene oxide (rGO) (Type 2 device). Three types of alcohols viz., methanol, ethanol, and 2-propanol, in the concentration range of 1–800 ppm were considered as the test species for the above-mentioned two types of sensor devices and the results were compared with those of the pristine ZnO NTs based device also. It was found that the sensing performance of the modified devices (both Type 1 and Type 2) was remarkably improved compared to that of its pristine counterpart in terms of response magnitude, response time, and recovery time. The Pd–ZnO NTs hybrid structure offered better sensing performance toward methanol, while the rGO–ZnO NTs hybrid structure offered the same toward ethanol. The underlying sensing mechanism for such improvement of the modified devices toward a specific alcohol species was also elucidated correlating the molecular size of the target species, respective dissociative electron attachment (DEA), and associated band diagram of the hybrid structures.

Influence of transition metal alloying and surface modification of the CdTe quantum dots on their optical properties, band structure and electrochemical activity

We report a study of CdTe quantum dots modification bythe alloying of with Zn2+ and Hg2+ ions and shell growth. Optical and cyclic voltammetry measurements were used to explain changes in the band structure of the particles via shell growth and during the alloying. Influence of stabilizer on the electrochemical behavior of the particles is also discussed. Obtained nanostructures demonstrate photoluminescence in the wider range of wavelengths than pure CdTe QDs.

Coupling Plant-Derived Cyclotides to Metal Surfaces: An Antibacterial and Antibiofilm Study.

Modification of metal surfaces with antimicrobial peptides is a promising approach to reduce bacterial adhesion. Here, cyclic peptides or cycloids, possessing remarkable stability and antimicrobial activities, were extracted and purified from Viola philippica Cav., and identified using mass spectrometry. Cyclotides were subsequently utilized to modify stainless steel surfaces via polydopamine-mediated coupling. The resulting cyclotide-modified surfaces were characterized by Fourier transform infrared (FTIR) spectroscopy and contact angle analysis. The antibacterial capacity of these cyclotides against Staphylococcus aureus was assessed by Alamar blue assay. The antibiofilm capacity of the modified surfaces was assessed by crystal violet assay, and scanning electron microscopy (SEM). A composite of Kalata b1, Varv A, Viba 15 and Viba 17 (P1); Varv E (P2); and Viphi G (P3) were isolated and identified. FTIR analysis of the modified surfaces demonstrated that cyclotides bound to the surfaces and induced reduction of contact angles. Antimicrobial effects showed an order P3 > P1 and P2, with P3-treated surfaces demonstrating the strongest antibiofilm capacity. SEM confirmed reduced biofilm formation for P3-treated surfaces. This study provides novel evidence for cyclotides as a new class for development of antibacterial and antibiofilm agents.

The most stable adsorption geometries of two chiral modifiers on Pt(111)

The molecular description of chirality transfer on chirally modified metal surfaces is unclear due to the complexity of the systems and the weak energetic biases favoring specific enantioselective pathways. In order to move to an enhanced level of molecular understanding it is critical to define the chemisorption geometries of the modifiers responsible for enantiodifferentiation. Model surface science studies of chiral molecules on single crystals provide an indirect method to probe catalytic chirality transfer molecular mechanisms. Apart from the great difference between ultrahigh vacuum (UHV) and reaction conditions, the extent to which such studies can inform the interpretation of data obtained under reaction conditions depends on the degree to which the model systems are correctly defined. The same holds true for any comparison of UHV surface spectroscopy data to spectroscopic measurements made at the catalyst-solution interface under either in-situ or operando conditions.We present detailed reflection absorption infrared spectroscopy (RAIRS) data on (R)-1-(1-naphthyl)ethylamine, (R)-NEA, and its simple derivative, (R)-1-(8-methyl-1-naphthyl)ethylamine, on Pt(111). Various conflicting proposals for the structure of NEA and analogous modifiers on Pt catalyst particles and extended Pt surfaces are found in the literature. Here, we find that below high sub-monolayer coverages on Pt(111), (R)-NEA adopts a chemisorption geometry where the entire naphthyl group is π-bonded to the surface and the amine group forms a dative bond to the surface. The same general adsorption geometry is found for the methyl-substituted derivative. The study provides reference spectra for these chiral modifiers and confirms the molecular structures described in our previous studies of diastereomeric complexes formed by the (R)-NEA/Pt(111) system.

A homogeneous focusing system for diode lasers and its applications in metal surface modification

High power diode lasers are applied in many different areas, including surface modification, welding and cutting. It is an important technical trend in laser processing of metals in the future. This paper aims to analyze the impact of the shape and homogeneity of the focal spot of the diode laser on surface modification. A focusing system using the triplet lenses for a direct output diode laser which can be used to eliminate coma aberrations is studied. A rectangular stripe with an aspect ratio from 8:1 to 25:1 is obtained, in which the power is homogeneously distributed along the fast axis, the power is 1117.6 W and the peak power intensity is 1.1587 × 106 W/cm2. This paper also presents a homogeneous focusing system by use of a Fresnel lens, in which the incident beam size is 40 × 40 mm2, the focal length is 380 mm, and the dimension of the obtained focal spot is 2 × 10 mm2. When the divergence angle of the incident light is in the range of 12.5–20 mrad and the pitch is 1 mm, the obtained homogeneity in the focal spot is the optimum (about 95.22%). Experimental results show that the measured focal spot size is 2.04 × 10.39 mm2. This research presents a novel design of homogeneous focusing systems for high power diode lasers.

Delamination Kinetics of Thin Film Poly(acrylate) Model Coatings Prepared by Surface Initiated Atom Transfer Radical Polymerization on Iron

Living radical polymerization is often considered as an unsuitable method of surface modification for reactive metals such as iron. Necessary noble metal catalyst systems may react with the surface to be modified, causing deactivation of the catalyst. Here, surface-initiated atom transfer radical polymerization (SI-ATRP) using the typical CuI-based catalyst was used to synthesize well-defined poly(methyl methacrylate) thin films grafted on iron. Alkoxy- and chloro-silane initiators were anchored to the metal surface via Si-O-Fe bonds in a metal pretreatment step, yielding a thin cross-linked multilayer sol/gel coating. Except for the precursor’s leaving group, the resulting 10s of nm thick polymer layers were almost identical. Assessment of the delamination kinetics of the model coatings by scanning Kelvin probe (SKP) showed the average delamination to be ≈ 40 % lower in the systems with alkoxy-precursor compared to those with chloro-precursor. In addition, the spread of the measured delamination rates decreased to 1/3 in the alkoxy system, despite identical polymers. The higher delamination rate in the case of chloro-precursors was attributed to residual chloride at the interface. Initiator surface coverage differences may also contribute to stability differences. The ATRP-CuI-catalyst is consequently also suitable for surface modification of non-noble metals after appropriate pretreatment.

Development and experimental study of large size composite plasma immersion ion implantation device

Plasma immersion ion implantation (PIII) overcomes the direct exposure limit of traditional beam-line ion implantation, and is suitable for the treatment of complex work-piece with large size. PIII technology is often used for surface modification of metal, plastics and ceramics. Based on the requirement of surface modification of large size insulating material, a composite full-directional PIII device based on RF plasma source and metal plasma source is developed in this paper. This device can not only realize gas ion implantation, but also can realize metal ion implantation, and can also realize gas ion mixing with metal ions injection. This device has two metal plasma sources and each metal source contains three cathodes. Under the condition of keeping the vacuum unchanged, the cathode can be switched freely. The volume of the vacuum chamber is about 0.94 m3, and maximum vacuum degree is about 5 × 10−4 Pa. The density of RF plasma in homogeneous region is about 109 cm−3, and plasma density in the ion implantation region is about 1010 cm−3. This device can be used for large-size sample material PIII treatment, the maximum size of the sample diameter up to 400 mm. The experimental results show that the plasma discharge in the device is stable and can run for a long time. It is suitable for surface treatment of insulating materials.

Surface modification of valve metals using plasma electrolytic oxidation for antibacterial applications: A review.

Plasma electrolytic oxidation (PEO) is an advance technique to develop porous oxidation layer on light metals, primarily to enhance corrosion and wear resistance. The oxidation layer can also offer a wide variety of mechanical, biomedical, tribological, and antibacterial properties through the incorporation of several ions and particles. Due to the increasing need of antimicrobial surfaces for biomedical implants, antibacterial PEO coatings have been developed through the incorporation of antibacterial agents. Metallic nanoparticles that have been employed most widely as antibacterial agents are reported to demonstrate serious health and environmental threats. To overcome the current limitations of these coatings, there is a significant need to develop antibacterial surfaces that are not harmful for patient's health and environment. Attention of the readers has been directed to utilize bioactive glasses as antibacterial agents for PEO coatings. Bioactive glasses are well known for their excellent bioactivity, biocompatibility, and antibacterial character. PEO coatings incorporated with bioactive glasses can provide environment-friendly antimicrobial surfaces with exceptional bioactivity, biocompatibility, and osseointegration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 590-605, 2018.

Engineering the internal surfaces of three-dimensional nanoporous catalysts by surfactant-modified dealloying

Tuning surface structures by bottom-up synthesis has been demonstrated as an effective strategy to improve the catalytic performances of nanoparticle catalysts. Nevertheless, the surface modification of three-dimensional nanoporous metals, fabricated by a top-down dealloying approach, has not been achieved despite great efforts devoted to improving the catalytic performance of three-dimensional nanoporous catalysts. Here we report a surfactant-modified dealloying method to tailor the surface structure of nanoporous gold for amplified electrocatalysis toward methanol oxidation and oxygen reduction reactions. With the assistance of surfactants, {111} or {100} faceted internal surfaces of nanoporous gold can be realized in a controllable manner by optimizing dealloying conditions. The surface modified nanoporous gold exhibits significantly enhanced electrocatalytic activities in comparison with conventional nanoporous gold. This study paves the way to develop high-performance three-dimensional nanoporous catalysts with a tunable surface structure by top-down dealloying for efficient chemical and electrochemical reactions.

Plasma surface modification in liquid environment

Plasma modification of metal surfaces in liquid environment was described. Microstructure and microhardness of a hardened layer were studied. As a result of plasma impact during 0.1-1 sec, the surface is carburized and nitrated to the concentration of highcarbon steel. Microstructure and metal surface properties after plasma modification were studied. Main parameters of the modified layer were identified: the layer depth is 50-300 μm, microhardness is 6000–14000 MPa.

Hemocompatibility of hyaluronan enhanced linear low density polyethylene for blood contacting applications.

Despite their overall success, different blood-contacting medical devices such as heart valves, stents, and so forth, are still plagued with hemocompatibility issues which often result in the need for subsequent replacement and/or life-long anticoagulation therapy. Consequently, there is a significant interest in developing biomaterials that can address these issues. Polymeric-based materials have been proposed for use in many applications due to their ability to be finely tuned through manufacturing and surface modification to enhance hemocompatibility. In this study, we have developed a novel, hydrophilic biomaterial comprised of an interpenetrating polymer network (IPN) of hyaluronan (HA) and linear low density polyethylene (LLDPE). HA is a highly lubricous, anionic polysaccharide ubiquitously found in the human body. It is currently being investigated for a vast array of biomedical applications including cardiovascular therapies such as hydrogel-based regenerative cell therapies for myocardial infarction, HA-coated stents, and surface modifications of polyurethane and metals for use in blood-contacting implants. The aim of this study was to assess the in vitro thrombogenic response of the hydrophilic polymer surface, HA-LLDPE for future potential use as flexible heart valve leaflets. The results indicate that HA-LLDPE is non-toxic and reduces thromobogenicity as compared to LLDPE surfaces, asserting its feasibility for use as a blood-contacting biomaterial. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1964-1975, 2018.

Biomimetic PDMS-hydroxyurethane terminated with catecholic moieties for chemical grafting on transition metal oxide-based surfaces

The aim of this work was to synthesize a non-isocyanate poly(dimethylsiloxane) hydroxyurethane with biomimetic terminal catechol moieties, as a candidate for inorganic and metallic surface modification. Such surface modifier is capable to strongly attach onto metallic and inorganic substrates forming layers and, in addition, providing water-repellent surfaces. The non-isocyanate route is based on carbon dioxide cycloaddition into bis-epoxide, resulting in a precursor bis(cyclic carbonate)-polydimethylsiloxane (CCPDMS), thus fully replacing isocyanate in the manufacture process. A biomimetic approach was chosen with the molecular composition being inspired by terminal peptides present in adhesive proteins of mussels, like Mefp (Mytilus edulis foot protein), which bear catechol moieties and are strong adhesives even under natural and saline water. The catechol terminal groups were grafted by aminolysis reaction into a polydimethylsiloxane backbone. The product, PDMSUr-Dopamine, presented high affinity towards inhomogeneous alloy surfaces terminated by native oxide layers as demonstrated by quartz crystal microbalance (QCM-D), as well as stability against desorption by rinsing with ethanol. As revealed by QCM-D, X-ray photoelectron spectroscopy (XPS) and computational studies, the thickness and composition of the resulting nanolayers indicated an attachment of PDMSUr-Dopamine molecules to the substrate through both terminal catechol groups, with the adsorbate exposing the hydrophobic PDMS backbone. This hypothesis was investigated by classical molecular dynamic simulation (MD) of pure PDMSUr-Dopamine molecules on SiO2 surfaces. The computationally obtained PDMSUr-Dopamine assembly is in agreement with the conclusions from the experiments regarding the conformation of PDMSUr-Dopamine towards the surface. The tendency of the terminal catechol groups to approach the surface is in agreement with proposed model for the attachment PDMSUr-Dopamine. Remarkably, the versatile PDMSUr-Dopamine modifier facilitates such functionalization for various substrates such as titanium alloy, steel and ceramic surfaces.

Combined plasma surface modification of austenitic stainless steel for bipolar plates

A fundamental study of a new concept for surface modification of metal surfaces based on two consecutive processes – metal coating and plasma nitriding – is conducted in order to obtain thin plasma-nitrided diffusion layers on austenitic stainless steels enriched with the metal from the coating, with superior surface characteristics with respect to the bipolar plate application of proton-exchange membrane fuel cells. The special feature of the concept is that the metal coating is permeable to the nitrogen diffusion into the base material.Austenitic stainless steel sheets EN 1.4301 with a thickness of 0.1mm are coated with chromium films in the range of 5–200nm by means of magnetron sputtering deposition. Subsequently, short-time plasma-nitriding by means of the strip hollow-cathode method is applied. The diffusion layers are analysed taking into account the nitrogen diffusion into the base material, diffusion processes at the interface between the chromium coating and the base material, the distribution of the elements, and the phase formation, in particular the formation of chromium nitrides. Further investigations are performed to determine the influence of applied plasma treatment on the electrical conductivity and corrosion resistance of the stainless steel surfaces.