Chemical nature of superhydrophobic aluminum alloy surfaces produced via a one-step process using fluoroalkyl-silane in a base medium

Various surface characterization techniques were used to study the modified surface chemistry of superhydrophobic aluminum alloy surfaces prepared by immersing the substrates in an aqueous solution containing sodium hydroxide and fluoroalkyl-silane (FAS-17) molecules. The creation of a rough micronanostructure on the treated surfaces was revealed by scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) and infrared reflection absorption spectroscopy (IRRAS) confirmed the presence of low surface energy functional groups of fluorinated carbon on the superhydrophobic surfaces. IRRAS also revealed the presence of a large number of OH groups on the hydrophilic surfaces. A possible bonding mechanism of the FAS-17 molecules with the aluminum alloy surfaces has been suggested based on the IRRAS and XPS studies. The resulting surfaces demonstrated water contact angles as high as ~166° and contact angle hystereses as low as ~4.5°. A correlation between the contact angle, rms roughnesses, and the chemical nature of the surface has been elucidated.     

Effect of a new low pressure SF6 plasma sterilization system on polymeric devices

A low pressure RF remote plasma, with low temperature, was used as new sterilization system. This system was designed especially for thermo-sensitive materials. SF₆ plasma has been found to totally inactivate all investigated microorganisms within three minutes. The effect of the SF₆ plasma treatment (soft conditions) and following the aging on three polymers films has been investigated.The evolution of surface after plasma treatment was studied by several techniques. FTIR was used to follow the degradations and changes in the bulk polymers. The SEM images showed the etching and grafting on the polymers surfaces. The decreasing of the wettability in the treated surfaces indicates an increasing in surface hydrophobicity. The decreasing of C and O atoms on the surface and the developing of non-polar sites (F functionalities) were observed by XPS analysis. The surface modifications were found to be permanent.     

Use of hydration inhibitors to improve bond durability of aluminium adhesive joints

The adsorption of selected organic hydration inhibitors onto Forest Products Laboratory (FPL)-etched aluminium surfaces and the subsequent hydration of the treated surfaces have been studied using X-ray photoelectron spectroscopy (XPS) and surface behaviour diagrams (SBDs) supplemented by Fourier Transform Infra-red Spectroscopy (FTIR). Wedge tests were used to evaluate performance of these inhibitors in improving bond durability and the locus of failure was identified by XPS and high resolution scanning electron microscopy (X-SEM). The results indicate that nitrilotris methylene phosphonic acid (NTMP) and related compounds adsorb to the alumina surface via the POH bonds of the phosphonic acid groups, resulting in a displacement of water normally adsorbed onto the surface. A model of adsorption was developed which suggests that after treatment with very low concentrations of inhibitor (1 ppm), only one leg of the NTMP molecule adsorbs onto the surface although at higher concentrations (100 ppm) all three legs adsorb. Hydration is a three-step process: (i) reversible physisorption of water; (ii) slow dissolution of the inhibitor followed by rapid hydration of the freshly exposed Al₂O₃ to boehmite (AlOOH); and (iii) further hydration of the AlOOH to bayerite [Al(OH)₃]. Analysis of the adsorption, hydration, and wedge test results using different inhibitors suggests the following five inhibitor characteristics that promote good bond performance: (i) displacement of water and occupation of all active sites on the Al₂O₃ surface; (ii) formation of strong inhibitor surface bonds; (iii) insolubility of the resulting inhibitor-aluminium complex in aqueous solutions; (iv) compatibility with the adhesive or primer; (v) coupling of the inhibitor to the adhesive.     

Microstructured bioreactive surfaces: covalent immobilization of proteins on Au(1 1 1)/silicon via aminoreactive alkanethiolate self-assembled monolayers

Micrometer-scale patterns of a defined surface chemistry and structure were produced on both ultraflat Au(1 1 1) and on gold-coated monocrystalline silicon surfaces by a method combining microcontact printing, wet chemical etching and the replacement of etch-resist self-assembled monolayers (SAMs) by functionalized or reactive SAMs. Key steps in this methodology were characterized by X-ray photoelectron spectroscopy (XPS), ellipsometry and contact angle measurements. The covalent immobilization of (functional) biological systems on these surfaces was tested using an N-hydroxysuccinimide ester -functionalized disulphide (DSU), which covalently binds primary amines without the need for further activation steps. Atomic force microscope images of native collagen V single molecules immobilized on these patterned surfaces revealed both high spatial resolution and strong attachment to the monolayer/gold surface. Microcontact printing of DSU is shown to be feasible on specially prepared, ultraflat Au(1 1 1) surfaces providing a valuable tool for scanning probe experiments with biomolecules. The retention of enzymatic activity upon immobilization of protein was demonstrated for the case of horseradish peroxidase. The described approach can thus be used to confine biological activity to predetermined sites on microstructured gold/silicon devices – an important capability in biomedical and biomolecular research. © 1999 Kluwer Academic Publishers     

Adhesive properties of polypropylene (PP) and polyethylene terephthalate (PET) film surfaces treated by DC glow discharge plasma

In this study, the adhesive properties of the plasma modified polypropylene (PP) and polyethylene terephthalate (PET) film surfaces have been investigated. Hydrophilicity of these polymer film surfaces was studied by contact angle measurements. The surface energy of the polymer films was calculated from contact angle data using Fowkes method. The chemical composition of the polymer films was analyzed by X-ray photoelectron spectroscopy (XPS). Atomic force microscopy (AFM) was used to study the changes in surface feature of the polymer surfaces due to plasma treatment. The adhesion strength of the plasma modified film was studied by T-peel strength test. The results showed a considerable improvement in surface wettability even for short exposure times. The AFM and XPS analyses showed changes in surface topography and formation of polar groups on the plasma modified PP and PET surfaces. These changes enhanced the adhesive properties of polymer film surfaces.     

静电自组装表面修饰HA/PA6膜:表征及其细胞相容性研究

通过表面改性引入活性生物分子可以用来增强材料表面的生物相容性。采用静电自组装技术将明胶和聚乙烯亚胺引入羟基磷灰石/聚酰胺6(HA/PA6)材料表面,最终获得大分子修饰的复合材料。利用水接触角测量(WCA)、X射线光电子能谱(XPS)和原子力显微镜(AFM)测试手段对表面改性前后HA/PA6膜的表面化学、亲水性和表面形貌进行表征。并研究了其对细胞活性的影响。结果表明,改性后膜表面的亲水性增强,粗糙度增大。体外细胞实验表明,明胶涂层后的HA/PA6表面细胞更利粘附、铺展和生长。该固定方法模拟细胞外基质组成制备出的生物活性膜能进一步满足生物医学工程需求。     

Surface modification of polystyrene using polyaniline nanostructures for biomolecule adhesion in radioimmunoassays

The selection of an appropriate surface as a solid phase for coupling antibodies is a critical step in the development of solid-phase immunoassays. Availability of a new method of preactivating the surface of polystyrene tubes with a layer of another polymer for enhanced immobilization of antibodies seems to be promising. In this paper, we report the activation of a polystyrene surface using a layer of polyaniline and its effect on immobilizing antibodies for use as a solid phase in a T3 immunoassay. The modified surface on the polystyrene was characterized by optical absorption, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The modified tubes were coated with antibody and evaluated for their performance in the assay and validated for radioimmunoassay of T3. AFM images of the modified surface showed an enhancement in the surface roughness (Ra of 20.2 nm), as compared to an unmodified surface (Ra of 6 nm), allowing more adsorption of antibodies to the surface. XPS revealed the presence of N (binding energy approximately 400 eV) on the modified surface, which could help the antibody molecules to bind to these preactivated (modified) tubes. The modified tubes, when coated with antibody, not only showed an increase in the binding with the radioiodinated tracer but also improved the precision of coating the antibody. The present method of activating polystyrene surfaces is simple, does not involve severe chemical treatment, and may have wide applicability to functionalize other supports for immobilizing biomolecules.     

Poly(dimethylsiloxane)-polyimide blends in the formation of thick polyimide films

Thick polyimide layers can be formed by using some unique properties of poly(dimethylsiloxane)-polyimide (PDMS/PMDA–ODA) blends followed by surface modification and deposition of a second layer of polyimide precursor chemicals. The method is based on the micro-phase separation characteristics of these blends to yield surfaces that have PDMS-like character. Upon modification with UV/ozone treatment, a surface that is essentially SiO _x and hydrophilic in nature is produced. This surface is amenable to reaction and deposition of a second polyimide layer from polyimide precursors. The thicker polyimide layer has enhanced adhesion between the original layer of the blend and the new polyimide layer and this approach finds extensive applications for products that require thick polymer layers. Changes in surface energy for various blend compositions were monitored by measurement of advancing contact angle with de-ionized water. Contact angle for unmodified polyimide films was on the order of 70° and it increased to about 104° after blending with PDMS and curing. UV/ozone treatment reduced the contact angle of the doped polyimide to less than 5°. X-ray photoelectron spectroscopy (XPS) and angle resolved XPS (ARXPS) measurements were used to monitor the chemical compositions of the various surfaces. High-resolution XPS spectra in the Si2p region confirm the transformation of O–Si–C bonds in PDMS to SiO _x , where x is about 2. Scanning electron microscopy (SEM) of some selected samples shows that the blends contain phase separation of the polymers at the surfaces of the samples. Atomic force microscopy (AFM) of siloxane-free polyimide, and PDMS/PMDA–ODA blends both prior to and after UV/ozone exposure, show that the films are essentially flat at short treatment times (less than 60 min). AFM also reveals the separation of PDMS into micro-domains at the cured film surface and throughout the layer below the surface of the blended films. Adhesion of a subsequently deposited polyimide layer to the modified polyimide surface was found to be greatly improved when compared to the adhesion obtained for deposition onto a pristine polyimide surface.     

Desmutting of aluminium alloy 2024-T3 using rare earth electrolyte

Abstract

The desmutting of 2024-T3 aluminium alloy using a new rare earth desmutting solution has been studied by SEM and X-ray photoelectron spectroscopy (XPS). It was evident from SEM that, during desmutting, there was dissolution and etching of both the intermetallics and the basic oxide scale left after alkaline cleaning. In addition, copper from the intermetallics was deposited as a residue on the surface of the desmutted alloy. The residue, in the form of precipitates ～200 nm in size, proved to be copper with an oxide coating. The addition of oxidants such as hydrogen peroxide (H₂O₂ ) and potassium persulphate (K₂ S₂O₈ ) removed these precipitates. It was apparent from XPS that the surface was coated with a thin 6 nm aluminium oxide after desmutting.     

Polypropylene non-woven fabric membrane via surface modification with biomimetic phosphorylcholine in Ce(IV)/HNO3 redox system

Surface modification of polypropylene non-woven fabric membrane (NWF) for improving its hemocompatibility was developed by grafting a biomimic monomer, 2-methacryloyloxyethyl phosphorycholine (MPC). The NWF membrane surface was first activated by potassium peroxydisulfate to form hydroxyl groups, and then grafted with MPC using ceric (IV) ammonium nitrate as the redox initiator. The surface chemical changes before and after modification were confirmed by Fourier transform infrared spectroscopy with an ATR unit (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS); the water contact angle results showed the gradual changes in wettability from hydrophobic to hydrophilic surface. Meanwhile, the hemocompatibility of these samples was also evaluated by protein adsorption and platelet adhesion. These experimental results exhibited that the introduction of poly(MPC) onto the NWF membrane surfaces substantially improved their hemocompatibility. The feasibility and simplicity of this procedure may lead to potential applications of NWF membranes in biomedical separation and blood purification.     

Simulation and modeling of self-assembled monolayers of carboxylic acid thiols on flat and nanoparticle gold surfaces

Quantitative analysis of the 16-mercaptohexadecanoic acid self-assembled monolayer (C16 COOH-SAM) layer thickness on gold nanoparticles (AuNPs) was performed using simulation of electron spectra for surface analysis (SESSA) software and X-ray photoelectron spectroscopy (XPS) experimental measurements. XPS measurements of C16 COOH-SAMs on flat gold surfaces were made at nine different photoelectron emission angles (5-85° in 10° increments), corrected using geometric weighting factors and then summed together to approximate spherical AuNPs. The SAM thickness and relative surface roughness (RSA) in SESSA were optimized to determine the best agreement between simulated and experimental surface composition. On the basis of the glancing-angle results, it was found that inclusion of a hydrocarbon-contamination layer on top the C16 COOH-SAM was necessary to improve the agreement between the SESSA and XPS results. For the 16 COOH-SAMs on flat Au surfaces, using a SAM thickness of 1.1 ?/CH(2) group, an RSA of 1.05, and a 1.5 ? CH(2)-contamination overlayer (total film thickness = 21.5 ?) for the SESSA calculations provided the best agreement with the experimental XPS data. After applying the appropriate geometric corrections and summing the SESSA flat-surface compositions, the best fit results for the 16 COOH-SAM thickness and surface roughness on the AuNPs indicated a slightly thinner overlayer with parameters of 0.9 ?/CH(2) group in the SAM, an RSA of 1.06 RSA, and a 1.5 ? CH(2)-contamination overlayer (total film thickness = 18.5 ?). The 3 ? difference in SAM thickness between the flat Au and AuNP surfaces suggests that the alkyl chains of the SAM are slightly more tilted or disordered on the AuNP surfaces.     

Surface analysis of NBR and HNBR elastomers modified with different plasma treatments

In this work, three rubber-like materials (NBR 7201, NBR 9003 and HNBR 8001) with applications in the automotive industry were studied. Different atmospheric pressure plasma treatments were used to modify the surface properties of these materials in order to improve their tribological behaviour. Surface analyses of the samples by means of X-ray photoelectron spectroscopy (XPS) were performed in order to get information about the surface chemistry and the elemental composition of the contact surfaces. In addition, wetting experiments were also carried out by measuring the contact angle of water drops on the surfaces using the sessile drop method. The XPS results showed a modification of the surface composition in both NBR rubbers, mainly due to an increase in the oxygen content, while the same treatments produced only slight modifications on the surface composition of the HNBR. The combination of N₂ and CH₃COOH during the plasma operation produced the strongest modifications of the surface composition of the tested elastomers. All these surface modifications also produced a change in the wetting of the rubber-like materials. The results revealed that the plasma treatments modified the hydrophobicity of the rubber-like NBRs.     

Dissolution of calcite crystals in the presence of some metal ions

A constant composition method has been used for the study of the kinetics of calcium carbonate (calcite) dissolution in which the activities of ionic species in relatively undersaturated solutions are maintained constant. Over a range of relative undersaturation (0.032–0.158) the dissolution reaction appears to be controlled by a bulk diffusion process. The suggestion of a predominantly diffusion-controlled process was supported by the observed low activation energy (2.09 kcal mol^–1). The influence of a number of metal ions on the reaction rate has been investigated. The retardation effect of these additives has been attributed to the blocking of active sites by adsorption of metal ions at the crystal surfaces. Inhibition of dissolution by metal ions can be interpreted in terms of a Langmuir isotherm.     

Correlation between Lewis donor/acceptor properties determined by XPS and Brönsted acid/base properties determined by rest-potential measurements,for aluminium and silicon oxides

In order to qualify the reactivity of various aluminium and silicon oxide substrates for elastomer adhesion applications, X-ray photoelectron spectroscopy (XPS) and rest-electrochemical potential measurements have been performed on those surfaces. The interpretation of XPS binding energy shift measurements in terms of Fermi level variation from one surface to another, as proposed by Mullins and Averbach in 1988, is discussed in view of results on an aluminosilicate compound surface. The correlation with electrochemical restpotential measurements on an anodized aluminium surface and a silane coupling agent is described and discussed. The possibility of surface reactivity assessment through correlated XPS and electrochemical measurements for metal oxides is demonstrated.     

Effect of alloying addition of Pr on the dissolution rate of melt-spun Mg in 3% NaCl solution

Melt-spun Mg-1 and 15 wt % Pr binary alloys were immersed in a 3% NaCl solution saturated with Mg(OH)2 for up to 72 h. The dissolution rate was evaluated by hydrogen evolution method. Surface characterization of the pristine and corroded surfaces has been carried out using X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The surfaces of both the pristine and corroded samples were found to consist mainly of Mg(OH)2 and MgO. However, results of XRD and SEM showed that the dominant product formed on the corroded sample was Mg(OH)2. SIMS depth profiling showed that there was a depletion of Pr at the surfaces of Mg–Pr samples. © 1998 Chapman & Hall     

Influence of oxygen and nitrogen plasma treatment on polyethylene terephthalate (PET) polymers

In this paper we present surface modification of polyethylene terephthalate (PET) polymer, which is commonly used as synthetic vascular graft. Surface modification was made by oxygen and nitrogen plasma at different treatment times. Plasma was created by means of an RF generator at a discharge power of 200 W and gas pressure fixed at 75 Pa. The surface of PET polymer was modified in order to achieve improved attachment of fucoidan, which is a bioactive coating with antithrombogenic properties. In our study we analysed chemical modification of plasma treated surfaces by X-ray photoelectron spectroscopy (XPS), while the changes in morphology and surface roughness were observed with atomic force microscopy (AFM). Our results indicate that attachment of fucoidan is improved by oxygen plasma treatment, especially due to surface roughening.     

Microstructural and chemical surface and rim zone changes of ferrite-perlite 42CrMo4 steel after electrochemical machining

Electrochemical machining is based on the anodic dissolution of most metals and generates high quality polished surfaces. However, ferrite-perlite 42CrMo4 steel reveals local optical changes at the surface after electrochemical finishing, such as a widely variable surface finish from shiny (reflective) to rough (dark) surfaces even after one processing step. The optical different surface areas of ferrite-perlite 42CrMo4 steel (AISI 4140) are studied by different electron microscopy techniques, x-ray diffraction and x-ray photoelectron spectroscopy to gain information about the local chemistry of the reaction layers and residual stresses of the rim zone. The results show that the rim zone for the different surface areas are about 50 nm–100 nm thick and contain oxygen. Selected area diffraction reveals the formation of iron(II/III) oxide (Fe₃O₄) and x-ray photoelectron spectroscopy confirms the formation of a mixed iron oxide (Fe_3-xO₄) with a variation of the oxidation state for both near-surface rim zones. Furthermore, the reflective surfaces reveal a homogeneous dissolution of ferrite and cementite lamellae whereas the rough surfaces show a preferred dissolution of cementite and an inhomogeneous dissolution of ferrite within the rim zone. X-ray diffraction measurements do not show any introduced residual stresses in the rim zone.     

Surface oxide dissolution in titanium subhydrides studied by Auger electron spectroscopy and X-ray photoelectron spectroscopy

The surface sensitive spectroscopic techniques of Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) have been applied to the study of oxide dissolution of titanium subhydrides. In an earlier study using AES, it was shown that the rate of oxygen dissolution into titanium increased sharply at ~350° C. These data correlated well with physical property measurements that indicated an exothermic reaction was occurring at these temperatures which corresponded to the reaction of free titanium with atmospheric oxygen. In the present study the work has been expanded to include studies of TiH _x (x=1.15, 1.62). It has been found that dissolution of the native oxide on titanium subhydrides occurs at a temperature substantially higher (~ 500° C) than that required for titanium. It appears that the outward diffusion of hydrogen is inhibiting the inward diffusion of oxygen on the subhydride samples at temperatures below 500° C.Mound Facility is operated by Monsanto Research Corporation for the United States Department of Energy under Contract Number DE-AC04-76-DP00053.     

铝合金表面微波等离子体类聚乙二醇涂层的亲水性研究

通过对铝合金低温微波等离子体表面改性,增强其亲水性,减少铝离子扩散,降低生物学毒性,可提高铝合金的生物相容性.采用三乙二醇二甲醚有机试剂,于电子回旋共振低温微波等离子体条件下,在铝合金表面进行沉积对其改性,对所得涂层用X射线光电子能谱、衰减全反射红外光谱和水接触角进行分析表征,以判断表面沉积物的组成及亲水性变化,评价低温微波等离子体处理对提高铝合金亲水性的机理及作用.结果表明,铝合金经三乙二醇二甲醚低温微波等离子体改性后,表面得到一层均匀、致密的涂层,其化学组成为类聚乙二醇结构,表面主要聚集有大量的碳氢和碳氧极性键;与改性前相比,等离子体涂装的铝合金表面接触角大大下降.低温微波等离子体表面改性能显著提高铝合金表面的亲水性.     

Effects of plasma oxidation on the surface and interfacial properties of ultra-high modulus carbon fibres

An ultra-high modulus (UHM) carbon fibre was submitted to an oxygen plasma treatment. The effects of this treatment on the physical and chemical properties of the carbon surfaces were investigated by using surface characterisation techniques. SEM and STM studies were performed in order to determine the changes in the surface morphology. Observations on the nanometre scale lead to the conclusion that the plasma oxidation “cleaned” the original surfaces of carbonaceous impurities. XPS analysis of the treated fibres revealed a very significant increase of oxygen content. Single-fibre epoxy composites were prepared from as-received and plasma-treated fibres, and fragmentation tests were performed in order to characterise fibre/matrix interfacial adhesion. Raman spectroscopy has been used to map the strain along the fibre during tensile loading of the matrix, and the distribution of interfacial shear stress has been obtained. The quality of the interface improved dramatically after the surface treatment, supporting the ability of cold plasma oxidation to enhance the adhesion of UHM carbon to epoxy matrices. It is concluded that the increase of the oxygen surface content and the removing of the outermost layers may contribute in a co-operative way to the improvement on fibre/matrix adhesion.