N. Brack

Cerium Dibutylphosphate as a Corrosion Inhibitor for AA2024-T3 Aluminum Alloys

The suitability of cerium dibutylphosphate [Ce(dbp) 3 ] as a corrosion inhibitor for AA2024-T3 aluminum alloy in sodium chloride aqueous solutions has been investigated. Weight loss tests combined with electrochemical assessment have been used to evaluate the degree of protection and determine the inhibition characteristics of this compound. It was found that Ce(dbp) 3 offers superior protection when compared to CeCl 3 , with no discernable corrosion products, significant pitting, or evidence of replated copper on the surface. Cathodic polarization indicated inhibited oxygen reduction reaction kinetics consistent with reduced Cu replating. Corrosion protection seems to be enhanced at higher Cl - concentrations, suggesting the inhibiting film is more readily deposited when some corrosion takes place. X-ray photoelectron spectroscopy analysis of the surface confirmed the presence of both Ce(III) and Ce(IV). Focused ion beam secondary-ion mass spectroscopy (SIMS) analysis clearly indicated the presence of a 500 nm thick cerium-containing layer on the surface of the alloy after 10 days immersion in the inhibited solution. A strong phosphorus signal was also detected in the SIMS experiment. Toxicity testing using the EC-50 test suggested that cerium dibutylphosphate is able to fulfil the basic requirements for consideration as an environmentally friendly corrosion inhibitor.

Contact angle measurement and surface energetics of sized and unsized paper

Abstract Determining the surface free energy of paper from contact angle data for various liquids is not straight forward and the results can sometimes be misleading. For insufficiently sized paper, errors may arise from rapid penetration of liquid probes into the sheet, which prevents accurate measurement of contact angles. For well-sized paper, errors may arise from factors associated with the roughness of the sheet. Despite the fact that some of the sources of error are well known, contact angle methods are still favoured for determining the surface free energy of paper. In this study, we focus on some factors associated with the topographical and chemical heterogeneity of paper (particularly sized sheets) that may cause contact angle data to lead to incorrect prediction of surface energetics. Whatman filter paper with and without calendering and AKD sizing treatment was used as a model system for studying the effect of sheet surface heterogeneity. To evaluate the sheet surface roughness at an interfibre pore level, the contact area between a water drop and the sized sheet surface was studied using confocal laser-scanning microscopy (CLSM). For well-sized sheets the actual contact area between the drop and the sheet was much smaller than the apparent contact area. The chemical heterogeneity of the sized filter paper sheets was studied using XPS and IGC. Both techniques again showed that the surfaces of well sized papers still possess acid and base polarities that are capable of interacting with liquid or vapour probes with acid and base functionality. Poor liquid–sheet contact area, however, acts as a factor that limits the number of acid–base adducts formed across the liquid–sheet interface. A possible way of correcting for the effect of sheet surface roughness on the apparent liquid–sheet contact angle using the Cassie–Baxter equation was tested.

Effects of Plasma Treatment of Wool on the Uptake of Sulfonated Dyes with Different Hydrophobic Properties

A wool fabric has been subjected to an atmospheric-pressure treatment with a helium plasma for 30 seconds. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry confirmed removal of the covalently-bound fatty acid layer (F-layer) from the surface of the wool fibers, resulting in exposure of the underlying, hydrophilic protein material. Dye uptake experiments were carried out at 50°C to evaluate the effects of plasma on the rate of dye uptake by the fiber surface, as well as give an indication of the adsorption characteristics in the early stages of a typical dyeing cycle. The dyes used were typical, sulfonated wool dyes with a range of hydrophobic characteristics, as determined by their partitioning behavior between water and n-butanol. No significant effects of plasma on the rate of dye adsorption were observed with relatively hydrophobic dyes. In contrast, the relatively hydrophilic dyes were adsorbed more rapidly (and uniformly) by the plasma-treated fabric. It was concluded that adsorption of hydrophobic dyes on plasma-treated wool was influenced by hydrophobic interactions, whereas electrostatic effects predominated for dyes of more hydrophilic character. On heating the dyebath to 90°C in order to achieve fiber penetration, no significant effect of the plasma treatment on the extent of uptake or levelness of a relatively hydrophilic dye was observed as equilibrium conditions were approached.

Surface modification of electrospun fibres for biomedical applications: A focus on radical polymerization methods.

The development of electrospun ultrafine fibres from biodegradable and biocompatible polymers has created exciting opportunities for biomedical applications. Fibre meshes with high surface area, suitable porosity and stiffness have been produced. Despite desirable structural and topographical properties, for most synthetic and some naturally occurring materials, the nature of the fibre surface chemistry has inhibited development. Hydrophobicity, undesirable non-specific protein adsorption and bacterial attachment and growth, coupled with a lack of surface functionality in many cases and an incomplete understanding of the myriad of interactions between cells and extracellular matrix (ECM) proteins have impeded the application of these systems. Chemical and physical treatments have been applied in order to modify or control the surface properties of electrospun fibres, with some success. Chemical modification using controlled radical polymerization, referred to here as reversible-deactivation radical polymerization (RDRP), has successfully introduced advanced surface functionality in some fibre systems. Atom transfer radical polymerization (ATRP) and reversible addition fragmentation chain transfer (RAFT) are the most widely investigated techniques. This review analyses the practical applications of electrospinning for the fabrication of high quality ultrafine fibres and evaluates the techniques available for the surface modification of electrospun ultrafine fibres and includes a detailed focus on RDRP approaches.

X-ray photoelectron emission microscopy and time-of-flight secondary ion mass spectrometry analysis of ultrathin fluoropolymer coatings for stent applications.

Fluoropolymer plasma coatings have been investigated for application as stent coatings due to their chemical stability, conformability, and hydrophobic properties. The challenge resides in the capacity for these coatings to remain adherent, stable, and cohesive after the in vivo stent expansion, which can generate local plastic deformation of up to 25%. Plasma-coated samples have been prepared by a multistep process on 316L stainless steel substrates, and some coated samples were plastically deformed to mimic a stent expansion. Analyses were then performed by X-ray photoelectron spectroscopy (XPS), X-ray photoelectron emission microscopy (X-PEEM), and time-of-flight secondary ion mass spectrometry (TOF-SIMS) to determine the chemical and physical effects of such a deformation on both the coating and the interfacial region. While XPS analyses always showed a continuous coating with no significant effect of the deformation, TOF-SIMS and near-edge X-ray absorption fine structure (derived from X-PEEM) data indicated the presence of a certain density of porosity and pinholes in all coatings as well as sparse fissures and molecular fragmentation in the deformed ones. The smallness of the area fraction affected by the defects and the subtlety of the chemical changes could only be evidenced through the higher chemical sensitivity of these latter techniques.

Comparative analysis of Ti3SiC2 and associated compounds using x-ray diffraction and x-ray photoelectron spectroscopy

Ti3SiC2 exhibits a unique combination of ceramic and metallic properties suitable for both electrical and mechanical application. With high-temperature stability, high electrical and thermal conductivity and resistance to oxidation, Ti3SiC2 has proven promising as a contact layer for high power SiC semiconductors. However, until recently, synthesis of this material has proven difficult without appreciable quantities (<2 vol{%}) of impurity phases, namely TiC1-x and Ti5Si3Cx. As such, many properties of this compound are as yet unknown. In this paper, a comparable analysis of Ti3SiC2 and associated compounds, TiC and Ti5Si3Cx has been performed using both x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). Assessing impurity sensitivities for each technique, XRD was shown to readily identify impurities of TiC and Ti5Si3Cx within Ti3SiC2 at <2 wt{%}. Although XPS could not independently resolve these impurities, its use resulted in the detection of a complex oxide structure on Ti3SiC2. It was speculated that it was composed of mixed C-Ti-C-O and Si-Ti-C-O bond chemistries. In a comparison of TiC, Ti5Si3Cx and Ti3SiC2, differences in oxide states suggest that oxidation is chemically dissimilar for all the three compounds. However, upon etching, the binding energies of Ti3SiC2 and Ti5Si3Cx were shown to be very similar. It may be concluded that a concurrent analysis of both XRD and XPS was essential for identifying the overall surface chemistry of Ti3SiC2.

A comparative study between the adsorption and covalent binding of human immunoglobulin and lysozyme on surface-modified poly(tert-butyl methacrylate).

The adsorption and covalent immobilization of human immunoglobulin (HIgG) and lysozyme (LYZ) on surface-modified poly(tert-butyl methacrylate) PtBMA films have been evaluated using x-ray photoelectron spectroscopy (XPS), ellipsometry and atomic force microscopy (AFM). Surface modification of PtBMA (UV irradiation) afforded surfaces suitable for both the physical and covalent attachment of proteins. The XPS and ellipsometry results showed good correlation in terms of variable-dense/thickness protein layer formation between physisorbed and covalently bound proteins. The amount of physisorbed HIgG ranged from 23.0 +/- 1.6 ng mm(2) on PtBMA, with corresponding film thicknesses 17.0 +/- 1.2 nm. Covalent immobilization mediated through 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)/N-hydroxysulfosuccinimide (sulfo-NHS) coupling chemistry, afforded 5.6-8 ng mm(2) of HIgG with a corresponding thickness of 5.9 +/- 0.6 nm on PtBMA. The attachment of LYZ to modified PtBMA surface was similarly translated, where adsorption yielded up to 15 ng mm(2), while covalent immobilization afforded typically 7-8 ng mm(2). The thickness of the adsorbed LYZ protein layer was 11.0 +/- 3.2 nm (PtBMA), suggesting the greater portion of protein adsorbs on surface-modified PtBMA.

The influence of hydroxyl group concentration on epoxy–aluminium bond durability

The influence of hydroxyl group (OH) concentration on the durability of adhesive bonds formed between an epoxy resin and aluminium adherend has been examined. Initially, surface analysis in combination with chemical derivatisation was employed to characterise the OH and epoxy functional groups present in FM-73, a structural epoxy adhesive. Bulk FM-73 indicated a higher degree of cure than the surface of FM-73 present at the interface of an epoxy–aluminium adhesive joint. Plasma and water treatment of the aluminium adherend was employed to alter the metal oxides surface OH concentration. Despite a several-fold difference of aluminium surface OH concentrations for the different metal pre-treatments, there was no significant variation in the adhesive joint fracture toughness in a humid environment, G Iscc. In contrast, grit-blasting the aluminium prior to bonding increased G Iscc almost 15-fold. Simple calculations indicate that the aluminium surfaces used in the bonding experiments would have a large excess of OH groups available to react with a standard epoxy resin and that the influence of surface roughness on adhesion durability is not insignificant.

Disposable biochip fabrication for DNA diagnostics

The need for disposable diagnostic sensors in the health care industry has been a major factor in the development of low-cost microfluidic devices. Polymer materials have been the obvious choice due to their cost effectiveness. However, these materials often do not possess the desired properties for biochip operation, such as their high non-specific binding and poor electroosmotic flow characteristics. Various fabrication techniques have also been developed for polymeric chips over the past few years due to their incompatibility with the traditionally preferred micromachining technologies associated with glass and silicon. This paper presents a method for constructing microfluidic devices in Poly(ethylene terephthalate) (PET) using a direct-write Neodymium Yttrium Aluminium Garnet (Nd:YAG) laser system. Issues involving the operation and fabrication of such disposable devices, with particular emphasis on the development of a bio-chip for DNA diagnostics, are discussed.

Mechanism of AKD migration studied on glass surfaces

Abstract Alkyl ketene dimers are widely used in sizing treatment of paper products. It is known that a good sizing effect can only be developed after the sized paper is cured at elevated temperatures. It is generally accepted that AKD re-distributes on the surface of the fibres during curing. The mechanism that dominates the re-distribution of AKD during curing is not fully understood and contradictory opinions can be found in the literature. There have been speculations in the literature that AKD undergoes a spontaneous ‘flow-like’ spreading during curing, leading to the development of an adequate sizing effect of paper. Other studies have suggested that AKD melt does not undergo a spontaneous spreading on the surface of smooth cellulose films. Some authors stressed that the vaporisation/deposition of AKD also plays a significant role in AKD sizing. The re-distribution of AKD in the curing process of papermaking is complicated and may involve the spreading of AKD melt, which is driven by the surface tension and/or the capillary forces, and the evaporation/re-deposition of AKD vapour. In this work, we examined the mechanism of AKD re-distribution on a smooth hydrophilic surface. By excluding the influence of porosity, this study allows us to focus on the effect of interfacial energetics on the possible spreading of AKD and the development of a sizing effect. Glass was used to provide the model for this study. AFM and XPS were used to monitor the spreading of AKD on the glass surface before and after curing. The Wilhelmy method was used to monitor the development of a sizing effect on the glass surfaces. Our results show that AKD wax does not undergo a macroscopic ‘flow-like’ spreading on the glass surface at a temperature well above the AKD melting point within the time scale of the experiment. A sizing effect developed more rapidly on areas of the glass surface which were covered with AKD than on areas that were initially not covered by AKD, since in the latter case sizing develops purely via exposure of the glass surface to AKD vapour. This implies that the distribution of AKD on the glass surface is likely to be very uneven on a microscopic scale. However, such an uneven distribution of AKD does not affect the development of a good macroscopic sizing effect on the glass surface.