Publications (8)14.57 Total impact
- [Show abstract] [Hide abstract] ABSTRACT: Time of flight secondary ion mass spectrometry (ToF-SIMS) has been employed for the study of the adsorption of epoxy resin molecules, diglycidyl ether of bisphenol A (DGEBA), on aluminium substrates treated with an organosilane, γ-glycidoxypropyltrimethoxysilane (GPS). Both the kinetics of adsorption and the thermodynamics have been examined, by the construction of adsorption isotherms. The kinetics of adsorption was investigated to establish an exposure equilibrium time for DGEBA adsorption onto GPS-treated aluminium. Specimens were treated with three different concentrations of DGEBA solution and six times of treatment. It was found that DGEBA molecules were adsorbed on the aluminium substrate and reached a true adsorption equilibrium after 10 min. Adsorption isotherms were then produced to define the type of adsorption. Two possible types of adsorption isotherms, Langmuir and Temkin, were examined, and DGEBA adsorption was found to be of the Langmuir type, providing a better fit than Temkin adsorption. Using a modified form of the Langmuir equation, the fractional monolayer coverage of DGEBA molecules was determined.
- [Show abstract] [Hide abstract] ABSTRACT: The degradation of a thin layer of adhesive on a grit-blasted aluminium substrate, as a result of aqueous attack, was investigated and compared with the behavior of the adhesive on a grit-blasted aluminium substrate treated with γ-glycidoxypropyl trimethoxy silane (GPS). The degradation study was achieved by examining aluminium coupons treated with adhesive that had been immersed in water at 25°C and an elevated temperature (50°C) for various treatment times ranging between 10 min and 1 day. All samples were characterized using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). XPS and ToF-SIMS data indicated that the adhesive layer on both types of substrate was readily displaced by water. This is shown to be a two-stage process with bond rupture being identified by ToF-SIMS analysis and the displacement of the organic phase occurring at a later stage, as indicated by the XPS analysis, which showed a reduction in surface carbon concentration. When the substrates were directly in contact with water, a hydration process occurred and hydrated oxide species were formed on the surfaces. The results indicated that the hydration process was a postfailure event.
- [Show abstract] [Hide abstract] ABSTRACT: The adsorption of a commercial adhesive and two of its major components—an amine curing agent [2,4-toluene diisocyanate urone (TDI urone)] and an adhesive prepolymer resin [diglycidyl ether of bisphenol A (DGEBA)]—on a hydrated aluminium surface and the hydrated surface coated with γ-glycidoxypropyltrimethoxysilane (GPS) has been investigated by x-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The study of TDI urone adsorption indicated that adsorption was of the chemisorption type, and a specific interaction involving this molecule and the GPS immobilized on the hydrated aluminium surface was identified. From XPS and ToF-SIMS data it was found that the types of interaction of the curing agent with the bare substrate were of the donor–acceptor type. Study of the DGEBA adsorption showed different-shaped isotherms for the bare and the GPS-coated substrates. It was found that the typical Langmuir isotherm type was obtained for the GPS-coated substrate whereas no adsorption plateau was observed for the bare substrate within the concentration range studied. This resulted from a change in the conformation of the DGEBA molecule on the substrate when the concentration of DGEBA solution was increased. The bonding of DGEBA with both types of substrates was assumed to be via acid–base interactions (i.e. donor–acceptor interactions). Adsorption of the commercial adhesive on the hydrated surfaces was of BET Type IV form, rather than the simple monolayer adsorption isotherm (Langmuir type). This indicates multilayer adsorption, presumably in the pores of the hydrated substrate, as a result of a process analogous to adsorption condensation. Copyright
- [Show abstract] [Hide abstract] ABSTRACT: Polysulphide sealants are now widely used to ensure the integrity of fuel tanks on both civil and military aircraft. The consequences of failure of such sealants are severe both in terms of the length of time that the aircraft will be removed from service and the nature of the remedial work that must be carried out within the tanks themselves. It was against this background that a recent multi-partner European Union Project MaSSPS (Materials System for Surface Protection and Sealing) was established. The members of the consortium include sealant manufacturers, aircraft manufacturers and other interested parties. The work to be presented in this paper concerns an extended study of the surface behaviour of candidate polysulphide sealant materials on exposure to water for times of up to 3 months. Coupons of research-grade sealants were immersed in ultrapure water at 25°C and 55°C in a thermostated water bath. These coupons were examined by XPS, using a Thermo VG Scientific Sigma Probe spectrometer with monochromated Al Kα radiation, and by ToF-SIMS, using a VG Scientific Type 23 instrument equipped with a two-stage reflectron analyser. Copyright
- [Show abstract] [Hide abstract] ABSTRACT: Study of the adsorption of polysulphide sealants with oxidized aluminium and oxidized aluminium treated with an organosilane adhesion promoter, γ-glycidoxypropyltrimethoxysilane (GPS), was achieved using XPS and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The kinetics and thermodynamics of adsorption have been investigated. The kinetics of adsorption were investigated to establish an exposure equilibrium time for the adsorption of polysulphide sealants onto both surfaces. Specimens were treated with polysulphide sealant solutions in toluene and different treatment times ranging from 30 s to 30 min. It was found that a 20 min treatment time allows the adsorption equilibrium of polysulphide sealants on both substrates to be reached. The thermodynamics of adsorption were studied as follows: all substrates have been treated with solutions of polysulphide sealants in toluene in a range of seven concentrations. Thermodynamic studies were carried out by the construction of adsorption isotherms. It was found that the polysulphide sealants adsorbed more on GPS-treated surfaces; on both surfaces, competition was observed between components present in the sealant formulation. The high-resolution C 1s XPS spectra were also peak fitted to account for the functional groups known to be present in the sealants and identified from ToF-SIMS data. Copyright © 2002 John Wiley & Sons, Ltd.
- [Show abstract] [Hide abstract] ABSTRACT: XPS and ToF-SIMS have been employed to study the interaction of solutions of a commercial dry film adhesive with grit-blasted aluminium and grit-blasted aluminium coated with an organosilane adhesion promoter, γ-glycidoxypropyltrimethoxy silane (GPS). From adsorption isotherm studies derived from XPS and ToF-SIMS results, it is shown that the adhesive uptake on both substrates was by chemisorption. The isotherm curves from XPS data indicated that the adhesive uptake on both substrates was similar. The uptake curves plotted using the relative peak intensity of ToF-SIMS characteristic fragment at m/z=58+ against the adhesive concentrations showed an important result. This fragment is characteristic of the curing agent as a result of chain scission of the end of the curing agent molecule. The adsorption isotherm demonstrated that the intensity for the grit-blasted surface was greater (by a factor of two) than that for a GPS coated surface. This is because on the bare surface, both ends of the molecule were available to yield the m/z=58 fragment, whereas on the GPS coated surface one end was immobilised by the interaction with the glycidoxy functionality.ToF-SIMS spectra exhibit a characteristic feature at m/z=277+ for both substrates. The presence of this ion is important evidence of a specific interaction occurring on both substrates. It was found that it is indicative of the formation of a covalent bond. On the surface not primarily treated with silane primer, the covalent bond is formed by partial crosslinking within the adhesive. On the surfaces treated with GPS and then the adhesive, this bond is from the interaction between the curing agent and either the epoxy functionality from the adhesive or the GPS.
- [Show abstract] [Hide abstract] ABSTRACT: The interaction of γ-glycidoxypropyltrimethoxysilane (GPS) with oxidised aluminium substrates has been investigated in terms of the effect of the drying, or curing, temperature. Samples treated with aqueous solutions of GPS at concentrations of 1,4 and 8% v/v were cured at 25, 50, 93 and 120°C. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to construct adsorption isotherms and determine the thicknesses of the various GPS coatings. A temperature effect induces subtle changes in the structure of the resulting films. The uptake of GPS is increasing with increasing concentration of GPS. The structure of the films changes at a threshold temperature between 50 to 93°C. XPS and ToF-SIMS data both indicate that the interaction of the GPS film on aluminium is different for low and high temperatures drying regimes. Using the Beer-Lambert equation, it was found that increasing the curing temperature leads to the variation of the thickness of silane films. This is interpreted in terms of changes in the crosslink density of the films and in their state of hydration and/or degradation.
- [Show abstract] [Hide abstract] ABSTRACT: Specimens treated with solutions of an epoxy analogue molecule, diethanolamine (DEA), have been studied by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF−SIMS). The initial substrates were of two different types: grit-blasted aluminum and aluminum coated with an organosilane adhesion promoter, γ-glycidoxy propyl trimethoxy silane (GPS). Specific interactions between the aluminum substrate and/or GPS treated aluminum and DEA are proposed on the basis of XPS and SIMS data. On oxidized aluminum, DEA forms either a single alkoxy or two alkoxy bonds (bridge). The formation of the so-called bridge brings the nitrogen atom close to the substrate. The nitrogen atom of DEA interacts with the surface via formation of a hydrogen bond or via donor−acceptor interaction with an aluminum atom. When deposited onto GPS-coated aluminum, DEA undergoes two types of interactions: formation of covalent bond with nucleophilic addition or Brönsted type of interaction between nitrogen of DEA and silanol functionality of hydrolyzed GPS.
University of Surrey
Guildford, ENG, United Kingdom
- Department of Mechanical Engineering Sciences