Application of ToF-SIMS surface analysis to tribochemistry in metal forming processes

Tribochemical properties are an essential component of the efficiency of metal forming lubricants. Their understanding, a basis for the selection of adequate additives, heavily relies on surface analytical techniques. In the last ten years, we have applied time-of-flight secondary ion mass spectroscopy (ToF-SIMS) to the analysis of the reactions of strip surfaces with typical additives of cold strip rolling and deep drawing lubricants. Data analysis procedures have been evolved to perform semi-quantitative comparisons. Analytical results performed on laboratory simulation tests and on real-size processes are compared. Examples of competition and synergies between different additives in a single lubricant are described.     

Characterisation of biological material with ToF-SIMS: a review

Abstract

Time of flight secondary ion mass spectrometry (ToF-SIMS) has the unique ability to simultaneously obtain chemical information (elemental and molecular) with its spatial distribution on a subcellular scale. Recent progress in instrumentation, in particular the developments of cluster ion beam sources, has resulted in a growing interest in applying ToF-SIMS to a range of biological samples. In this review, the instrumental and methodological approaches responsible for this interest are presented along with some examples where the technique has been successfully applied.     

Time-of-flight SIMS and in-situ XPS study of O2 and O2-N2 post-discharge microwave plasma-modified high-density polyethylene and hexatriacontane surfaces

The O₂ and O₂-N₂ ([N₂] < 15%) post-discharge microwave plasma modifications of high-density polyethylene (HDPE) and hexatriacontane (HTC) surfaces have been studied as a function of the distance from the discharge and the gas composition. They are compared in terms of the in-situ XPS O/C ratios and C 1s components, and the ex-situ ToF-SIMS O^-/CH^- ratios and relative intensities of series of peaks. The results on the effect of the distance from the discharge showed a clear correlation between the in-situ XPS results and the O₂ post-discharge modeling, exhibiting the double role of oxygen atoms: functionalization initialization by creating radicals (which react with molecular oxygen) and degradation due to the energy released by the oxygen atom recombination process. Specific in-situ XPS and ex-situ ToF-SIMS signatures of this in-situ degradation related to the oxygen atom recombination process were exhibited. When N₂ was introduced in the plasma gas, the in-situ XPS results and the ex-situ ToF-SIMS results were very different. The in-situ functionalization decreased as a function of the N₂ addition and the ex-situ functionalization exhibited a high maximum for the 5% N₂-95% O₂ post-discharge plasma and then decreased. Despite the absence of a complete O₂-N₂ post-discharge modeling, it can be assumed that there is also a maximum of the oxygen atom content for the 5% N₂-95% O₂ post-discharge. Thanks to the in-situ XPS and ex-situ ToF-SIMS specific signatures, it was also shown that this maximum corresponds to a low in-situ degradation effect. Nitrogen introduction could influence the role of oxygen atoms in such a way that there is a decrease in oxygen atom recombination processes (thus in degradation) for small N₂ addition and even a decrease in oxygen functionalization initialization for further N₂ incorporation in the plasma gas. No nitrogen was observed in the in-situ XPS results, whereas some ex-situ ToF-SIMS nitrogen-containing ions were observed for the O₂ and O₂-N₂ post-discharge. However, their relative intensities followed the variation in oxidation and not the variation in N₂ concentration in the plasma gas. They could be related to a post-treatment functionalization effect. Differences observed between HDPE and HTC are explained in terms of their structural differences (desorption of low molecular weight oxygen-containing fragments for HTC).     

Specific control of cell–material interactions: Targeting cell receptors using ligand-functionalized polymer substrates

Cells respond to their environment in complex and sometimes poorly understood ways. Protein, peptide and synthetic peptidomimetic ligands may all be used to stimulate cells via receptor signaling, using interactions that are often highly specific. Polymer substrates that present these ligands provide a promising way to control cell development, both for applications in biotechnology and for fundamental studies of cell biology. Here we review a large range of techniques that have been employed to create and characterize ligand-functionalized substrates, with a particular focus on techniques that allow specific and consistent stimulation.     

Phase identification and interfacial transitions in ternary polymer blends by ToF-SIMS

Phase identification and the study of the interphase region in multi-component polymer blends with a chemically similar structure using conventional techniques is a challenge. In this work, the detailed morphological analysis of such systems is examined. A ternary blend comprised of poly butylene succinate (PBS); poly lactic acid (PLA); and polycaprolactone (PCL) with a partial wetting morphology is carefully selected since all three components are polyesters with low interfacial tensions. It will be shown that a novel technique by applying multivariate analysis (MVA) on time-of-flight secondary ion mass spectrometry (ToF-SIMS) data can effectively identify the complex phase structure, especially in blends with chemically similar components. Furthermore, for the first time for such systems, this technique provides detailed information about interfacial thicknesses and transitions. By employing the principal component analysis (PCA) method on the ToF-SIMS data of pure polymers, specific peaks with a certain molecular ion mass related to each polymer are determined. Using overlaid mappings on the surface of the blend by ToF-SIMS and selected ion masses to identify each polymer results in the differentiation of the various phases represented as a morphological image. In a second step, the multivariate curve resolution (MCR) method is used as a “self modeling curve resolution” for the recovery of pure components from a multi-component mixture when little or no prior information is available. Total pseudo-color RGB images of PBS/PLA/PCL show that PLA droplets unambiguously partially wet the PBS and PCL phases. Since each pixel from the analysis in the high lateral resolution image represents a 200 nm diameter, the interfacial transitions can also be studied for both PLA/PBS and PLA/PCL interfaces. The results show the concentration variation of phases across the interfaces. A complete trace line across the two interfaces (PLA/PBS and PLA/PCL) allows for the quantitative determination of interfacial thickness for the first time for such systems.     

Interphase Chemistry: The Synergy of Surface Analysis,Surface Adsorption and Adhesion

The formation of an interphase zone at the junction between an organic system, such as an adhesive or coating, and an inorganic substrate is considered. Drawing on experimental work for a fully-formulated photocured resin and theoretical models for a simple homopolymer it is shown that such a feature may be the result of preferential adsorption (for a multicomponent system) or conformational changes in the case of a homopolymer. Guidelines for the recognition, cause and prediction of such layers are provided, and their possible effects on the strength and durability of the organic/inorganic couple are discussed. It is suggested that the consideration of these phenomena at the design stage of a new resin may provide a route to optimise hydrolytic stability. The behaviour of an interphase zone of this type as a weak boundary layer is also considered.     

Aliphatic hyperbranched polyesters based on 2,2-bis(methylol)propionic acid—Determination of structure, solution and bulk properties

Due to their highly branched structure and the large number of functional groups hyperbranched polymers possess unique properties that make them interesting for uses in a wide variety of applications. Some of the most widely investigated hyperbranched polymers are the polyesters based on 2,2-bis(methylol)propionic acid. In this paper we present the results of characterization studies of hyperbranched polyesters based on 2,2-bis(methylol)propionic acid which show that they are very complex products with a multidimensional distribution of various properties. The influence of the synthesis conditions on the structure and molar-mass characteristics of hyperbranched polyesters as well as the findings that allow a thorough understanding of the structure-property relationships are reviewed in detail.     

Electrochemical reactivity, surface composition and corrosion mechanisms of the complex metallic alloy Al3Mg2

A corrosion mechanism is proposed for Al₃Mg₂, based on electrochemical tests, XPS, and depth profiling using XPS and ToF-SIMS. After short (∼2 min) solution exposure, the surface consists of a surface film above dealloying. The dealloying is attributed to selective Mg dissolution and the surface rearrangement of Al into islands, although the metallic Al could alternatively be formed by two reduction reactions. The surface film thickness was ∼10 nm. After exposure to ultra-pure water, the composition was AlMg_1.3O_0.2(OH)_5.1 corresponding to Al(OH)₃·1.1 Mg(OH)₂·0.2MgO. After exposure to 0.01 M Na₂SO₄, the composition was AlMg_0.2O_0.4(OH)_2.5 corresponding to Al(OH)₃·0.1Al₂O₃·0.2MgO. Longer exposure produced a thicker surface film, more pronounced metallic Al islands and more MgH₂. Three possibilities are identified for MgH₂ formation. Al(OH)₃ formation is attributed to a precipitation reaction. Bulk nanoporous Al₃Mg₂ formation is predicted to be possible by Mg dealloying of Mg₁₇Al₁₂.     

Passivation behavior of Type 304 stainless steel in a non-aqueous alkyl carbonate solution containing LiPF6 salt

Passivation behavior of type 304 stainless steel in a non-aqueous alkyl carbonate solution containing LiPF₆ salt was studied using electrochemical polarization, X-ray photoelectron spectroscopy (XPS) and time of flight-secondary ion mass spectroscopy (ToF-SIMS). Cathodic polarization to 0 V vs. Li/Li⁺ resulted in most but not complete reduction of the air-formed film from oxides to metal on the stainless steel, as confirmed by XPS. For complete elimination of the air-formed film, the surface of the stainless steel was scratched under anodic polarization conditions. At 3 V vs. Li/Li⁺ where an anodic current peak appeared, only an indistinct layer was recognized on the newly scratched surface, according to ToF-SIMS analysis. Above 4 V vs. Li/Li⁺, substantial passive films were formed, which were composed of oxides and fluorides of iron and chromium. The origin of oxide was due to water contained in the non-aqueous alkyl carbonate solution, and that of fluorides were the result of the decomposition of electrolytic salt, LiPF₆, especially at higher potential. The resultant passive films were stable in the non-aqueous alkyl carbonate solution containing LiPF₆ salt.