Protection of iron corrosion by stearic acid and stearic imidazoline self-assembled monolayers

A type of stearic imidazoline (IM) inhibitor was prepared using stearic acid (SA) and diethylenetriamine (DETA) as raw materials. The monolayers of IM and SA were assembled on the iron surface. The electrochemical characterization of stearic acid (SA) and stearic imidazoline (IM) on an oxide free iron surface had been studied. The monolayers of IM inhibitor were characterized by electrochemical impedance spectroscopy (EIS), electrochemical polarization curves, double layer capacitance, X-ray photoelectron spectroscopy (XPS) and molecular simulation. The results of electrochemical studies had illustrated that the inhibition efficiency of IM was higher than SA. XPS showed that the IM molecules adsorbed on the iron surface. The molecular simulation calculations showed that the IM molecules were tilted at an angle on the iron surface.     

Synergistic inhibition effect of 2-mercaptobenzothiazole and Tween-80 on the corrosion of brass in NaCl solution

The corrosion inhibition of brass in 0.2 M NaCl in the presence of 2-mercaptobenzothiazole (MBT) and polyoxyethylene sorbitan monooleate (Tween-80) has been investigated using potentiodynamic polarization, X-ray photoelectron spectroscopy and inductively coupled plasma analysis. Analysis of the results revealed that the addition of MBT and Tween-80 inhibits the corrosion of brass in 0.2 M NaCl. Potentiodynamic polarization measurements showed that MBT acts as a mixed-type inhibitor and Tween-80 as an anodic inhibitor. Corrosion inhibition occurs through adsorption of the inhibitor on brass surface without modifying the corrosion mechanism. The adsorption of MBT and Tween-80 both follow Langmuir adsorption isotherm. Potentiodynamic polarization results suggested that the mixture of MBT and Tween-80 acts as a mixed-type inhibitor. Inhibition efficiency of 79.0 and 62.5% were obtained in the presence of optimum concentration of MBT and Tween-80, respectively. The addition of the mixture of MBT and Tween-80 enhanced the inhibition efficiency to 94.0% and showed a synergism of inhibition. XPS analysis indicated that MBT adsorbed on brass surface along with Tween-80 in the presence of the mixture of MBT and Tween-80. The results of solution analysis using ICP showed that the mixture of MBT and Tween-80 effectively controlled the dezincification of brass.     

Inhibition performance of 2-mercaptobenzothiazole derivatives in CO2 saturated solution and its adsorption behavior at Fe surface

Two 2-mercaptobenzothiazole derivatives, N,N′-bis-(2-thionobenzothiazolin-3-yl-methyl)-n-dodecylamine (BTBMDA) and N,N′-bis-(2-thionobenzothiazolin-3-yl-methyl)-n-octadecylamine (BTBMOA), were synthesized under microwave irradiation. Their inhibition performance for N80 steel in CO₂ saturated solution at 90 °C were tested by weight loss method and the surface analysis was performed by SEM. The adsorption behavior of two inhibitors at the Fe surface was studied by the molecular dynamics simulation method and the quantum chemistry calculations. Results showed that the two inhibitors could inhibit the corrosion of N80 steel in simulated solution significantly. There were two types of end configurations for two inhibitors at the Fe surface in the molecular dynamics simulation, and the two inhibitors adsorbed at the surface mainly through one of the two types.     

Synthesis and surface characterization of alkylthioacetyl-capped self-assembled monolayers on gold surface

A novel alkylthioacetyl-capped hydroxyethyl methacrylate monomer and its corresponding homopolymer have been synthesized and characterized. Direct chemisorption of these moieties have been carried out on gold-coated substrate and found to form a strong surface bonding. The surface coverage and the properties of the resultant self-assembled layers have been investigated by multiple surface characterization techniques (i.e. ellipsometry, GA-FTIR, XPS, AFM, and contact angle measurements). These analyses have all confirmed the occurrence of complete chemisorption reactions with typical n-alkanethiol self-assembled characteristics.     

Inhibition effect of self-assembled films formed by gold nanoparticles on iron surface

The self-assembled (SA) films formed by gold nanoparticles on iron surface had been proved to have inhibition effect for the substrate in 0.5 M H₂SO₄ solutions. The inhibition action was investigated using electrochemical impedance spectroscopy (EIS). The SA films formed by gold nanoparticles protected with sodium oleate had better corrosion protection to the iron substrate than only by sodium oleate. Scanning electron microscopy (SEM) was used to observe the imagines of the SA films. In addition, it was found that the gold nanoparticles could influence the nickel electroless plating films on the iron substrate. The structure and composition of the plating films were test by electron probe microanalyzer (EPMA). The mechanisms of the formation of the SA films and the nickel electroless plating reaction were also discussed.     

Self-assembled monolayers of flufenaminate anions on mild steel surface formed in aqueous solution

Adsorption of derivative of phenylanthranilic acid - flufenamic acid (FFA) on the “oxide-free” and oxidized surface of mild steel in neutral borate buffer solution was studied by ellipsometry and XPS. Anodic polarization curves reveal that complete suppression of the anodic dissolution of iron is achieved at FFA concentration C_in = 3.8 mM. Besides, adding FFA substantially shifts the pitting potential from 0.06 V to 0.67 V. Ellipsometric studies have shown that at the applied potential −0.65 V, when the surface is free from the oxide layer, FFA forms monomolecular layer. To characterize the surface layers formed after exposing the sample in 5 mM FFA solution the XPS was used to assess the composition and the thickness of the layers. Using the intensities of the Fe 2p, Fe 3p, N 1s, F 1s, O 1s and C 1s and analyzing the angle resolved XPS data the FFA molecules have been shown to form monomolecular layer in which FFA is (vertically or slightly inclined) anchored by iron cations through oxygen atoms of carboxyl group to the surface and the fluorine atoms of CF₃ groups form the utmost layer. Similar orientation is also assumed for FFA molecules adsorbed on the oxidized iron surface. It seems that the layer formed by FFA or similar molecules may serve a robust interface for grafting other substances on such a functionalized surface.     

乙醇溶剂中2-巯基苯并噻唑吸附于铁表面的SERS光谱研究

利用共焦显微拉曼系统研究了乙醇溶剂中2 巯基苯并噻唑(HMBT)在不同pH条件下吸附在ORC法粗糙化处理所得铁表面的SERS光谱。结果表明2 巯基苯并噻唑分子在酸性和中性溶液中通过环外S或环内N原子吸附于铁表面,而在碱性溶液中分子失去氢原子,并通过静电相互作用吸附于铁表面上。     

Characterization of the “native” surface thin film on pure polycrystalline iron: A high resolution XPS and TEM study

The characterization of the “native” surface thin film on pure polycrystalline iron has been studied by high resolution X-ray photoelectron (XP) spectroscopy of Fe 2p and O 1s regions. The film was allowed to form by exposing the sample to atmosphere at ambient conditions for a period of 1 h. The systematic approach used here includes the determination of curve fitting parameters from external standards and their use in fitting the raw data for the surface thin film. The quantitative high resolution XPS analysis involved an angle resolved study of the surface to determine the chemical composition and thickness of this native film. The film was found to be a mixture of Fe₃O₄ and Fe(OH)₂ with a thickness of 1.2 ± 0.3 nm. This conclusion is consistent with thermodynamics as indicated by the Pourbaix diagram for the Fe-H₂O system and the phase diagram for the Fe-oxygen system. A detailed TEM study of the native surface film also supports this conclusion.     

Step-wise decomposition process of azobenzene self-assembled monolayers

The step-wise decomposition of 4-(12-(dodecyldithio)dodecyloxy)azobenzene (AzoC24) in self-assembled monolayer (SAMs) on Au(1 1 1) was observed by thermal desorption spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS) under the ultra-high vacuum (UHV) condition. This decomposition process only occurred after the formation of the SAM.The TD spectra clearly showed two steps of thermal decomposition of the azobenzene moiety. At approximately 450 K, fragments of m/e = 77 and 105 were clearly observed. These fragments were decomposed species obtained by the breakage of the C-N bonds of the azobenzene moiety. At about 490 K, other fragment of m/e = 93 assigned to the phenoxy ion was detected. In order to examine the decomposition process, we measured the S 2p and N 1s XPS of the SAM at various temperatures. The results suggest that diazonium moiety is the first to be decomposed and the remaining structure is desorbed together with breakage of C-O bond between the phenoxy moiety and alkyl chain with increasing temperature.     

Characterization of a bioactive nanotextured surface created by controlled chemical oxidation of titanium

Events at bone-implant interfaces are influenced by implant surface properties. Our previous work has revealed that osteogenic activity is enhanced by a nanotextured Ti surface, obtained by controlled chemical oxidation using a H₂SO₄/H₂O₂ mixture. To better understand the origin of this biological effect, we have carried out a characterization of the modified surface at the nanoscale. In particular, the morphology, structure, and chemical composition of the Ti surface were examined thoroughly. X-ray photoelectron spectroscopy (XPS), combined with grazing-angle Fourier-transform infrared (FTIR) spectroscopy, revealed that the oxidized Ti surface consists of almost pure TiO₂ with Ti:O ratio ranging between 1:2.02 and 1:2.08. Raman spectroscopy and X-ray diffraction (XRD) indicated that the chemically treated Ti surface is mainly composed of amorphous titania. Scanning electron microscopy (SEM) clearly showed that the treated Ti substrate becomes highly porous and has a surface consisting of nano-sized pits, which have average diameters and fractal dimensions ranging between 20-22 nm and 1.11-1.17, respectively. Atomic force microscopy (AFM) revealed a three-fold increase in surface roughness. The thickness of the oxide layer on the treated Ti surface is estimated to be ∼32-40 nm. Together, these observations provide a detailed characterization of chemically oxidized Ti surfaces at the nanoscale and offer new prospects for understanding and controlling the relationship between the properties of materials and their interactions with cells. Our work brings us closer to the creation of “intelligent” implant surfaces, capable of selectively influencing cell behavior.     

Electrochemical and molecular simulation studies on the corrosion inhibition of 5,10,15,20-tetraphenylporphyrin adlayers on iron surface

5,10,15,20-Tetraphenylporphyrin (TPP) was synthesized and self-assembled on iron surface to form adlayers. Some surface analysis techniques such as XPS, FT-IR and SEM were performed to characterize the adlayers. The corrosion inhibition ability was investigated by using the technique of electrochemical impedance spectroscopy (EIS) and polarization curves in 0.5 M H₂SO₄. Results showed that the presence of the porphyrin adlayers was able to protect iron from corrosion effectively and longer immersion time would lead to better inhibition performance. In addition, molecular simulation studies were applied to optimize the adsorption structures of TPP molecules on iron surface. Calculated results indicated that the middle macrocycle of the TPP molecules assumed a nearly flat orientation with respect to the iron surface and the four centrosymmetric benzene rings were tilted by 44.8° and 58.8° because of the steric hindrance effect.     

Surface Analysis of Inhibitor Film Formed by 4-Amino-N-(1,3-thiazol-2-yl) Benzene Sulfonamide on Carbon Steel Surface in Acidic Media

Inhibitive properties of the antibacterial sulfa drug sulfathiazole—IUPAC name being 4-amino-N-(1,3-thiazol-2-yl) benzene sulfonamide—on the corrosion of carbon steel in 1.0 M HCl solution were investigated using weight loss measurements, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Sulfathiazole is a good adsorption inhibitor, and the inhibition efficiency increases with increasing concentration. Adsorption is spontaneous and is best described by Temkin isotherm. XPS analysis showed, at this stage, that the main product of corrosion is a nonstoichiometric Fe³⁺ oxide/oxyhydroxide consisting of a mixture of Fe₂O₃, α, and γ-FeO(OH) and/or Fe(OH)₃, where α, γ-FeO(OH) is the main phase.     

Characterization of silane layers on modified stainless steel surfaces and related stainless steel-plastic hybrids

The aim of this work was to characterize silane layers on the modified stainless steel surfaces and relate it to the adhesion in the injection-molded thermoplastic urethane-stainless steel hybrids. The silane layers were characterized with scanning electron microscope and transmission electron microscope, allowing the direct quantization of silane layer thickness and its variation. The surface topographies were characterized with atomic force microscope and chemical analyses were performed with X-ray photoelectron spectroscopy. The mechanical strength of the respective stainless steel-thermoplastic urethane hybrids was determined by peel test. Polishing and oxidation treatment of the steel surface improved the silane layer uniformity compared to the industrially pickled surface and increased the adhesion strength of the hybrids, resulting mainly cohesive failure in TPU. XPS analysis indicated that the improved silane bonding to the modified steel surface was due to clean Fe₂O₃-type surface oxide and stronger interaction with TPU was due to more amino species on the silane layer surface compared to the cleaned, industrially pickled surface. Silane layer thickness affected failure type of the hybrids, with a thick silane layer the hybrids failed mainly in the silane layer and with a thinner layer cohesively in plastic.     

ToF-SIMS investigation of FIB-patterning of lactoferrin by using self-assembled monolayers of iron complexes

Geometrically well-defined patterns of surface-immobilized proteins can be produced with several methods. We developed a method for patterning of proteins by means of specific, non-covalent interactions between a protein and a metal complex immobilized at the surface. In particular, reproducible patterns of lactoferrin have been obtained by exploiting the different adsorption properties of this protein on a OH-terminated self-assembled monolayer (SAM) or onto an iron-containing SAM present in certain regions of the pattern. The OH-terminated SAM was etched with a focused ion beam (FIB) in order to produce square regions of bare gold. These regions were selectively covered with a SAM of iron-terpyridine complex, formed via a stepwise procedure involving the initial formation of a mixed component SAM (containing the terpyridine ligand) and the subsequent reaction with an iron(II) salt in order to produce the complex. The patterned substrate was finally allowed to interact with a lactoferrin solution. It is shown that lactoferrin selectively and stably adsorbs on iron-containing layers, whereas it is not retained on the OH-terminated regions of the surface. The use of ToF-SIMS was crucial for obtaining this information, as well as for monitoring each sequential step necessary for the preparation of the patterns.     

Integrity of functional self-assembled monolayers on hydrogen-terminated silicon-on-insulator wafers

Silicon-on-insulator (SOI) wafers are commonly used to design microelectronics, energy conversion, and sensing devices. Thin solid films on the surfaces of SOI wafers have been a subject of numerous studies. However, SOI wafers modified by self-assembled monolayers (SAMs) that can also be used as functional device platforms have been investigated to a much lesser extent. In the present work, tert-butoxycarbonyl (t-boc, (CH₃)₃-C-O-C(O)-)-protected 1-amino-10-undecene monolayers were covalently attached to a H-terminated SOI (1 0 0) surface. The modified wafers were characterized by X-ray photoelectron spectroscopy to confirm the stability of the SAM/Si interface and the integrity of the secondary amine in the SAM. The transmission electron microscopy investigation suggested that this t-boc-protected 1-amino-10-undecene SAM produces atomically flat interface with the 2 μm single crystalline silicon of the SOI wafer, that the SiO_x and both available Si/SiO_x interfaces are preserved, and that the organic monolayers are stable, with apparent thickness of 1.7 nm, which is consistent with the result of the density functional theory modeling of the molecular features within a SAM.     

Protection of iron against corrosion by coverage with Au nanoparticles and n-hexylthiol mixed films

Through a one-step thermal reaction, Au nanoparticles were synthesized and self-assembled mixed films of Au nanoparticles and n-hexylthiol were prepared on iron surface. The size distribution and shape of Au nanoparticles were examined using transmission electron microscopy (TEM). Results of two electrochemical methods - electrochemical impedance spectroscopy (EIS) and polarization curves indicate that self-assembled mixed films can form on the iron surface and prevent it from corrosion effectively. Energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) measurements were applied to identify the formation of the mixed films on iron surface.     

An electrochemical study for corrosion inhibition of iron by some organic phosphonium chloride derivatives in acid media

The inhibiting action of (chloromethyl) triphenyl phosphonium chloride (CTP), tetraphenyl phosphonum chloride (TP), triphenyl phosphine oxide (TPO), triphenyl (phenylmethyl) phosphonium chloride (TPM) and triphenyl phosphine (TPP) on the corrosion of iron in 1 M HCl solution was studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Experimental results revealed that CTP, TP, TPO, and TPM act as inhibitors for iron in acid environments, while TPP is an accelerator. These compounds are mixed-type inhibitors and the inhibition efficiency increased with increasing concentrations. Equivalent circuits of the investigated systems are suggested.     

Evaluation of residual iron in carbon nanotubes purified by acid treatments

A detailed analysis by X-ray photoelectron spectroscopy was carried out on multi-walled carbon nanotube (MWCNT) surfaces after non-oxidative and oxidative purification treatments in liquid-phase. The MWCNT were produced by pyrolysis of camphor and ferrocene, that provides a high yield but with high iron contamination (∼15% wt). The elimination and/or oxidation of iron nanoparticles were monitored by Fe2p and O1s core level. Oxygen-based functional groups attachment was also investigated by C1s fitting. The effectiveness of each treatment in iron removal was evaluated by thermogravimetric analysis (TGA) and atomic absorption spectroscopy (AAS). The integrity of the MWCNT structure was verified by Raman spectroscopy (RS) and transmission electron microscopy (TEM). A purity degree higher than 98% was achieved only with non-oxidative treatments using sonification process.     

Improved aging performance of vapor phase deposited hydrophobic self-assembled monolayers

A hydrophobic self-assembled monolayer (SAM) of fluoro-octyl-trichloro-silane (FOTS) was deposited on silicon using a vapor phase technique. The aging of the hydrophobic layer was examined using water contact angle measurements. It has been found that while such monolayer films suffer from a loss of hydrophobicity with time, pre-immersion nitrogen annealing can significantly improve the aging characteristics of these monolayers. The effect of nitrogen annealing on the improved aging properties of SAM coatings has been investigated by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The hydrolytic stability and the effect of nitrogen annealing were studied by morphological evolution during immersion. A spontaneous formation of silane mounds on the surface of the monolayers was found by AFM. These mounds have been irreversibly transformed from initially uniform hydrophobic surface layers. It is highly probable that the compliance of these mounds can reasonably allow hydrophilic sites to be located around the mounds. Interestingly, the density of these mounds formation is very less on the annealed samples. XPS reveals a higher level of coverage by the N₂-annealed film due to agglomeration. A relative abundance of CF₃ and CF₂ moieties in the annealed film may explain the enhancement of the hydrophobicity as revealed by higher level of water contact angle. This hydrophobicity was found to be significantly stable in water. This novel finding explains the improved hydrophobic stability of FOTS monolayers as primarily a morpho-chemical effect that originates from the densification of the monolayers upon annealing.     

Control of surface properties of self-assembled monolayers by tuning the degree of molecular asymmetry

We have studied self-assembled monolayers (SAMs) of asymmetric dialkyldisulfide derivatives of the form CH₃-(CH₂)_11+m-S-S-(CH₂)₁₁-OH with m = −4, −3, 0, +2 and +4 on gold. Sub-nanoscale changes in the length of the CH₃-terminated alkylchain have been used to selectively protrude one particular end group in the resulting film. The alteration of the chain length in only two methylene units already results in changes of surface properties, which have been detected with local (chemical force microscopy) and macroscopic (contact angle) techniques. In particular, advancing contact angles can be adjusted between 40° and 80°. The adhesion between a hydrophobic tip and these SAMs in water is determined by the chemical nature of the protruding end group. Chemical force microscopy, X-ray photoelectron spectroscopy and infrared reflection absorption spectroscopy have shown that these SAMs are composed of mixed, well-packed CH₃- and OH-alkylthiolate branches. The surface composition ratio is close to 1:1 for all investigated SAMs.