Changes In Surface Composition Research Articles

Quantitative optical microspectroscopy, electron microscopy, and modelling of individual silver nanocubes reveal surface compositional changes at the nanoscale.

The optical response of metal nanoparticles is governed by plasmonic resonances, which depend often intricately on the geometry and composition of the particle and its environment. In this work we describe a method and analysis pipeline unravelling these relations at the single nanoparticle level through a quantitative characterization of the optical and structural properties. It is based on correlating electron microscopy with microspectroscopy measurements of the same particle immersed in media of different refractive indices. The optical measurements quantify the magnitude of both the scattering and the absorption cross sections, while the geometry measured in electron microscopy is used for numerical simulations of the cross section spectra accounting for the experimental conditions. We showcase the method on silver nanocubes of nominal 75 nm edge size. The large amount of information afforded by the quantitative cross section spectra and measuring the same particle in two environments, allows us to identify a specific degradation of the cube surface. We find a layer of tarnish, only a few nanometers thick, a fine surface compositional change of the studied system which would be hardly quantifiable otherwise.

The landscape-forming role of relief in the formation of the forest composition in the southwestern part of Moscow Oblast

«Вестник Санкт-Петербургского университета. Науки о Земле» — научно-теоретический рецензируемый журнал, обобщающий результаты исследований в области геологии, гидрогеологии и геохимии, петрологии и экологии, ландшафтного планирования и геоморфологии, экономической и социальной географии.

Stainless steel in simulated milk and whey protein solutions – Influence of grade on corrosion and metal release

Reactions at the biointerfaces between stainless steel and protein-rich dairy products, which contain whey proteins, are important to consider in terms of food safety and material grade selection. Changes in corrosion behavior, metal release, and surface composition of austenitic (AISI 316 L), ferritic (AISI 430), and lean duplex (LDX 2101) stainless steels in simulated milk (SMS) and whey protein solution were investigated. The amount of released metals and the corrosion susceptibility increased according to 2101 < 316 L < 430. All grades revealed low corrosion rates in the whey protein solution without any sign of active/metastable corrosion. Pitting corrosion was evident for 430 in SMS. The total amount of released metals (iron, chromium, and nickel) was significantly higher in whey protein solution compared with SMS. This suggests the metal release process to be mainly governed by complexation reactions. Nickel was preferentially released compared to its bulk composition fraction for both 316 L and 2101 in the highly complexing SMS. Reduced metal release rates with time correlated with the enrichment of chromium in the surface oxide. The extent of metal release was for all metals substantially lower than release limits of metals stipulated in health regulations related to the use of alloys and metals in food-related environments.

Dissolution of Stone Wool Fibers with Phenol-urea-formaldehyde Binder in a Synthetic Lung Fluid.

Mineral wool products, composed of stone wool fibers and organic binder, are used in many construction applications. Among all their beneficial properties, the most important requirement is safety for human health, such as when fibers are inhaled. For determining long-term toxicity, biosolubility and biopersistence studies in vitro and in vivo are essential. In vitro fiber dissolution rate, which depends on the medium, fiber composition, and the surface available for dissolution, is a key parameter in determining biopersistence of the material in vivo. We investigated how organic binder (phenol-urea-formaldehyde), which can partially shield fiber surfaces from the solution, influences fiber dissolution kinetics in synthetic lung fluid (modified Gamble's solution) at pH 4.5 and temperature 37 °C, in vitro. Dissolution experiments were made in batch and continuous flow using stone wool fibers with typical insulation product binder amounts (0-6 wt %), applied by the standard industrial process. Dissolution rates were determined from element concentrations in the reacted solution, and changes in fiber surface composition and morphology were monitored. Stone wool fiber dissolution was close to stoichiometric and was similar, whether or not the material contained binder. The high dissolution rate (508 ng of fiber/cm2/h) is explained by Al and Fe complexing agents, that is, citrate and tartrate, in the synthetic lung fluid. The organic binder mainly forms micrometer-sized discrete droplets on the fiber surfaces rather than a homogeneous thick coating. During in vitro tests, fibers with organic binder preferentially dissolved in the areas free of binder, forming cavities, whereas the untreated fibers dissolved homogeneously. Propagation of cavities undermined the binder droplets, leading to complete fiber dissolution. Thus, presence of organic binder on stone wool fibers, produced by the standard industrial process, had no measurable effect on dissolution rate in synthetic lung fluid containing Al and Fe complexing agents.

Two-step synthesis of few layer graphene using plasma etching and atmospheric pressure rapid thermal annealing

A two-step process using halogen based plasma etching combined with atmospheric pressure rapid thermal annealing has been used to synthesize few layer graphene films on 6H-SiC (0001) surfaces. In this process, the 6H-SiC substrates were etched under different plasma conditions to produce a carbon rich surface layer. This was followed by rapid thermal annealing in a flow of atmospheric pressure Ar to produce the graphene films. The effects of different etching conditions, heating rates, and average and maximum annealing temperatures were investigated. Changes in surface and near-surface composition after each step were characterized by x-ray photoelectron spectroscopy and overall film quality was assessed using Raman spectroscopy. Film defects associated with this synthesis method included a buffer layer between the SiC substrate and graphene as well as oxygen-based defects on the graphene surface. Electrical characterization of these films was performed using both two and four point methods. In the two point measurements, these films exhibited back-to-back Schottky behavior from which the Schottky barrier height, carrier density and mobility were determined. The four point measurements were used to determine the contact and film resistivity as well as the transfer length.

An Accurate Device for Apparent Emissivity Characterization in Controlled Atmospheric Conditions Up To 1423 K

Emissivity is a material property that must be measured before an accurate noncontact temperature measurement can be made. We have developed a novel instrument for measuring apparent emissivity under a controlled atmosphere, providing data for applications in radiation thermometry. Our instrument employs a split furnace, a sample-blackbody component, two custom-designed radiometers, and a controlled atmospheric system. We measure across the temperature range from 973 to 1423 K and the spectral range from 0.85 to 1.1 μm; this range is matched to the majority of high-temperature radiation thermometers. The sample and reference approximate blackbody are heated and maintained in the thermal equilibrium, with a temperature difference of better than 1 K at 1423 K. The combined standard uncertainty of the system is lower than 0.0590 (at k = 2) over the whole temperature range. Apparent emissivity of type 304 stainless steel (SS304) was studied under different oxidizing procedures. Nitrogen and compressed air were input into the system to control the oxidization process. We elucidated the relationship between the apparent emissivity variations and the surface composition changes of SS304 during oxidization. This article aims toward accurate and traceable apparent emissivity data, with well-investigated uncertainty, for use in radiation thermometry.

Highly Efficient AuPd Catalyst for Synthesizing Polybenzoxazole with Controlled Polymerization

Summary Using nanoparticles (NPs) to catalyze chemical reactions for the formation of functional polymers with controlled polymerization is an important field of chemical research. In this article, we report an AuPd NP system as an active and stable catalyst to catalyze one-pot reaction of formic acid, 1,5-diisopropoxy-2,4-dinitrobenzene, and terephthaldehyde, leading to the controlled polymerization and the formation of polybenzoxazole (PBO) (Mw = 3.6 kDa). The one-pot reaction is AuPd NP size and composition dependent, and 8-nm Au39Pd61 NPs are the best catalyst for the polymerization. The highly pure PBO shows excellent thermal stability up to 600°C and improved chemical and mechanical stability under challenging environmental conditions compared with commercial PBO (Zylon, Mw = 40 kDa). The reported NP-catalyzed one-pot reaction to polymerization is not limited to the formation of PBO but can be extended as a general approach to rigid polymers that are important for ballistic fiber, anti-flame, and smart-textile applications.

Electro-Responsive Surface Composition and Kinetics of an Ionic Liquid in a Polar Oil.

The quartz crystal microbalance (QCM) has been used to study how the interfacial layer of an ionic liquid dissolved in a polar oil at low weight percentages responds to changes in applied potential. The changes in surface composition at the QCM gold surface depend on both the magnitude and sign of the applied potential. The time-resolved response indicates that the relaxation kinetics are limited by the diffusion of ions in the interfacial region and not in the bulk, since there is no concentration dependence. The measured mass changes cannot be explained only in terms of simple ion exchange; the relative molecular volumes of the ions and the density changes in response to ion exclusion must be considered. The relaxation behavior of the potential between the electrodes upon disconnecting the applied potential is more complex than that observed for pure ionic liquids, but a measure of the surface charge can be extracted from the exponential decay when the rapid initial potential drop is accounted for. The adsorbed film at the gold surface consists predominantly of ionic liquid despite the low concentration, which is unsurprising given the surtactant-like structures of (some of) the ionic liquid ions. Changes in response to potential correspond to changes in the relative numbers of cations and anions, rather than a change in the oil composition. No evidence for an electric field induced change in viscosity is observed. This work shows conclusively that electric potentials can be used to control the surface composition, even in an oil-based system, and paves the way for other ion solvent studies.

Surface degradation of strontium-based perovskite electrodes of solid oxide fuel cells

Solid oxide fuel cells (SOFCs) are chemical-to-electrical energy conversion devices that consist of ceramic and metallic materials. The electrodes of SOFCs function as sites for electrochemical reactions, and as electronic conductors to transfer charge. The strontium-based perovskite electrode has been considered because it offers ionic and electronic conductivity, and tolerance to reduction-oxidation cycling. However, as shown in this work, exposure to humidity greater than 40% relative humidity, that may be present during non-operation conditions, including storage, can result in changes in the electrode surface composition with resulting degradation of electrical performance. This study investigates the physical-chemical and electrical characteristics of electrode surfaces when subjected to various humidity and temperature conditions, using scanning electron microscopy, energy dispersive spectroscopy, X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction techniques. Electrode phase decomposition, along with strontium-based degradation mechanisms, were found at humidity levels greater than 40% relative humidity.

SURFACE ABLATION OF 52100 BEARING STEEL USING FEMTOSECOND LASER IRRADIATION

Laser ablation is a rapid-material removal technique with potential application in remanufacturing of bearings to clean damaged surfaces. This study reports the ablation morphology and change in surface composition of 52100 bearing steel irradiated with a femtosecond laser. A smooth ablated surface was achieved by operating the laser at fluence just above the ablation threshold, but higher fluences resulted in roughened surfaces with recast formation. Such coarse morphology is believed to result from higher energy deposition and surface melting. Minimal oxidation occurred at lower fluences. Periodic ripple patterns formed in the ablated area at low fluence; their morphology and possible formation mechanism is discussed.

Surface Reconstruction by a Coassembly Approach.

Materials with switchable surfaces, capable of changing surface properties under external stimuli, are playing a pivotal role in many applications, such as tissue engineering, biosensors, and drug/protein delivery. In this research silica particles with patterned and switchable surfaces are fabricated. Surface micelles on silica particles are formed by coassembly of polymer brushes and "free" block copolymer chains in a selective solvent. The cores of the surface micelles are crosslinked by anthracene photodimerization. After quaternization of the coronae, amphiphilic surface micelles are prepared. The surface micelles are able to rearrange in different media. After treatment with an organic solvent, the surfaces of silica particles are occupied by hydrophobic polymer components; in aqueous solution, the positively charged polymer chains are on the surfaces. The switching of the surface micelles results in changes in surface composition and wetting behaviors.

Surface Reconstruction by a Coassembly Approach

AbstractMaterials with switchable surfaces, capable of changing surface properties under external stimuli, are playing a pivotal role in many applications, such as tissue engineering, biosensors, and drug/protein delivery. In this research silica particles with patterned and switchable surfaces are fabricated. Surface micelles on silica particles are formed by coassembly of polymer brushes and “free” block copolymer chains in a selective solvent. The cores of the surface micelles are crosslinked by anthracene photodimerization. After quaternization of the coronae, amphiphilic surface micelles are prepared. The surface micelles are able to rearrange in different media. After treatment with an organic solvent, the surfaces of silica particles are occupied by hydrophobic polymer components; in aqueous solution, the positively charged polymer chains are on the surfaces. The switching of the surface micelles results in changes in surface composition and wetting behaviors.

The influence of storage relative humidity on aerosolization of co-spray dried powders of hygroscopic kanamycin with the hydrophobic drug rifampicin

The purpose of this study was to investigate the influence of storage humidity on in vitro aerosolization and physicochemical properties of co-spray dried powders of kanamycin with rifampicin. The powders were stored for one-month in an open Petri dish at different relative humidities (RHs) (15%, 43%, and 75%) and 25 ± 2 °C. The in vitro aerosolization (fine particle fraction, FPF) of the powders was determined by a next generation impactor (NGI). The moisture content, particle morphology and crystallinity of the powders were determined by Karl Fischer titration, scanning electron microscopy, and X-ray powder diffractometry, respectively. At all RH, the FPF of hydrophobic rifampicin-only powder was unaffected but the FPF of hygroscopic kanamycin-only powder significantly decreased even at 43% RH. The kanamycin-only particles fused together, crystallized and formed hard cakes at 75% RH. The aerosolization of kanamycin and rifampicin in the combination powders remained unaffected at 15% and 43% RH, but aerosolization significantly decreased at 75% RH. Enrichment of the surface of the particles with hydrophobic rifampicin did not protect the combination powders from moisture uptake but it prevented particle agglomeration up to 43% RH. At 75% RH, the moisture uptake led to agglomeration of the particles of the combination powder particles and consequently an increase in aerodynamic diameter. Further studies are required to investigate how rifampicin enrichment prevents particle agglomeration, the possible mechanisms (e.g. particle interactions due to capillary forces or electrostatic forces) for the changes in the aerosolization and changes in surface composition during storage.

Glass Hardness Modification by Means of Ion Implantation: Electronic Doping versus Surface Composition Effect

AbstractCritical load measurements point to an improvement in the hardness of a soda–lime glass upon nitrogen implantation. In order to determine whether this improvement originates from electronic doping or surface composition changes induced by ion implantation, a theoretical approach using quantum‐chemical and force‐field methods combined with X‐ray photoelectron spectroscopy is performed. The results indicate that neither an electronic effect nor a lattice distortion appear to be the primary cause of the hardness improvement. It is rather a change in the surface composition leading to a more densely cross‐linked and stiffer silica network at the top surface of the glass which is at the origin of this improvement.

Solvent mediated inclusion of metal oxide into block copolymer nanopatterns: Mechanism of oxide formation under UV-Ozone treatment

Uniform, periodic and ordered iron oxide nanopatterns can be generated by selective metal ion inclusion into microphase separated polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer (BCP) thin films. After solvent mediated metal ion inclusion into the PEO block, an ultraviolet-ozone (UVO) treatment was used to remove the polymer and oxidize the metallic ions to their oxides. This paper provides an in-depth study of the UVO processing steps as a function of exposure time. Surface wettability, topography, morphology, compositional and interfacial changes were analysed by contact angle measurement, microscopic and spectroscopic techniques through the UVO treatment. It was found that the UVO treatment initially cross-links the polymer network followed by oxidation and removal of the polymer simultaneously. It was also found that if short UVO exposure times are used, a post calcination treatment can be used to generate similar patterns. The iron oxide nanopatterns created due to strong coordination bond between metallic ions and free electron pairs of O atoms in the PEO and these interactions are responsible for the final pattern mimicking the original self-assembled BCP morphology. The film thicknesses, surface roughness, the size/shape of the iron oxides and patterns, the amount of residual polymers were also investigated regarding the UVO exposure time.

Reactions at noble metal contacts with methylammonium lead triiodide perovskites: Role of underpotential deposition and electrochemistry

Chemical reactivity of halide perovskites coupled with a low energy of formation makes it a challenge to characterize material properties and achieve long-term device stability. In this study, we elucidate electrochemical reactions occurring at the methylammonium lead triiodide (MAPbI3)/Au interface. X-ray photoemission spectroscopy is used to identify a type of reduction/oxidation reaction termed underpotential deposition (UPD) involving lead, iodine, and hydrogen occurring at interfaces with noble metals. Changes in surface compositions and oxidation states suggest that UPD derived adsorbates at MAPbI3/Au interfaces lower the energy barrier for release of volatile HI and/or I2 catalyzing degradation at exposed contacts. Additionally, comparison to PbI2/Au interfaces demonstrates that the presence of methylammonium/methylamine accelerates the formation of a Pb0 adlayer on the Au. Reactions involving UPD Pb0 can transform the typically anodic (hole collecting) Au to a cathode in a photovoltaic measurement. Cyclic voltammetry reveals electrochemical reaction peaks in indium tin oxide (ITO)/MAPbI3/Au devices occurring within voltage ranges commonly used for perovskite characterization. The electrochemical stability window of this device architecture is measured to be between −0.5 V and 0.9 V. Voltage induced interfacial reactions contribute to reversible electrochemical peaks, hysteresis, switchable perovskite diode polarity, and permanent degradation at larger voltages. These types of surface reactions alter the interface/interphase composition beyond ion accumulation, provide a source for the diffusion of defects, and contribute to electrode material dependent current-voltage hysteresis. Moreover, the results imply fundamental limitations to achieving high device stability with noble metals and/or methylammonium containing perovskites.

Surface Treatment of Carbon Fibers by Oxy-Fluorination

In this paper, the oxy-fluorination process and the influence of different concentrations of fluorine and oxygen in the gas phase on the physicochemical properties of polyacrylonitrile(PAN)-based carbon fibers are described. The properties of the treated carbon structures are determined by zeta potential and tensiometry measurements. In addition, changes in surface composition and morphology are investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Adhesion properties are characterized by the single fiber pull-out (SFPO) test. Furthermore, changes in intrinsic properties are described by means of tensile and density measurements. After a primary desizing effect by oxy-fluorination, an increased number of oxygen-containing surface functional groups could be detected, which led to more debonding work in SFPOs with an epoxy-based matrix. It was also shown that the polar surface energy grows with rising fluorine concentration in the reaction gas mixture. In addition, a minor increase of ~10% in the maximum strength of PAN-based carbon fibers is detected by single fiber tensile measurements after oxy-fluorination with a fluorine content of 5% in the reaction mixture.

Time-dependent effect on wetting and tribological properties of plasma-modified acrylonitrile–butadiene rubber (NBR) surface

Different time air plasma treatment was conducted on acrylonitrile–butadiene rubber (NBR) surface, the wettability and friction behavior of the samples surface were measured after two months of storage. The changes in surface composition and microstructure during storage process were observed by X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM), respectively. The results show that the wettability of modified surface has obvious “hydrophobic recovery” phenomenon in the storage process, and the range of contact angle increase is closely related to the plasma treatment time, mainly because the change in surface composition at various time treatment are different during storage; the frictional behavior of plasma-modified NBR surface has not exhibited a “recovery” phenomenon after two months of storage, and the friction coefficient of the surface treated for 4 min and 8 min were even smaller than those before storage, which is due to the smoother and lower roughness of the surface morphology after storage. This study demonstrates that air plasma treatment is a promising technique for improving the wettability and tribological properties of NBR rubber, but the proper treatment time is needed to make the surface have the best wetting and frictional behavior.

Investigation on surface properties of superhydrophobic nanocomposites based on polyvinyl chloride and correlation with cell adhesion behavior

The main aim was to study the roles of structural homogeneity and superhydrophobicity on the adhesion of SW colon cancer cells on the surface of polyvinyl chloride (PVC) nanocomposites. Concurrent use of a proper nonsolvent (ethanol) and silica nanoparticles resulted in superhydrophobic behavior and also different surface structures. The effect of added‐ethanol content on the surface properties of PVC nanocomposites was also studied. The synergetic combination of silica and ethanol has led to the formation of a porous surface layer resulting in a considerable boost in the hydrophobic behavior. The scanning electron microscopy, roughness, and X‐ray photoelectron spectroscopy (XPS) analysis results were all in total agreement indicating the substantial change in surface morphology, topography, and composition once the ethanol content was increased to 50 vol.%. The surface structure was notably changed by the addition of polyhedral oligomeric silsesquioxanes (POSS) nanoparticles. It was found that the induced inhomogeneity as a result of POSS addition had an adverse effect on the surface properties. In conclusion, superhydrophobicity could be regarded as a prerequisite for achieving cell‐repellent behavior, but it cannot guarantee a cell repellent surface especially if the surface layer possesses structural inhomogeneity.

In vitro assessment of human enamel surface composition bleached with two different bleaching agents

Background: Varieties of methods are available for more obstinate tooth discoloration such as crowns, veneer, and micro and macro abrasion of enamel, but tooth bleaching gained high patient acceptance. The aim of the present research was to estimate changes in surface enamel composition after bleaching 16% carbamide peroxide (CP) (home-use bleaching) with 38% hydrogen peroxide (HP) (in office bleaching). Materials and Methods: A total of 90 enamel slabs from 45 sound human third molars were randomly divided into three groups. Of three groups, per group had thirty samples (n = 30), of which samples of Group 1 were placed in artificial saliva at 37°C in incubator (Memart, Germany) during complete experiment. Sample of Groups 2 and 3 was treated with power whitening gel (White Smile 2011, Germany) and tooth whitening pen (white Smile 2011, Germany), respectively. Later on, after bleaching treatment, discs were thoroughly washed and stored in artificial saliva at 37°C in incubator. Chemical analysis was done with energy dispersive spectroscopy (Edx) detector to detect changes in surface composition. Results: Energy dispersive X-ray spectroscopy (Edx) analysis showed no significant difference between all the three groups for Ca% mass (P > 0.99) and Ca% atomic (P > 0.99), C% mass (P = 0.78) and C% atomic (P = 0.76), and O% mass (P > 0.99) and O% atomic (P = 0.28). Similar results were shown for Na, Mg, P, and F. Conclusion: Statistically insignificant effect was observed on enamel composition with both bleaching agents (38% HP and 16% CP).