Marie-Laure Abel

The determination of the surface energy of conducting polymers by inverse gas chromatography at infinite dilution

Abstract Inverse gas chromatography (IGC) has been used at infinite dilution to determine the dispersive and acid–base contributions to the surface energy of inherently conducting polymer (ICP) powders and nanocomposites, with an emphasis on polypyrrole bulk powder. New and previously published results are discussed and show that polypyrrole and polyaniline are high-surface energy materials by contrast to conventional polymers and undoped poly(3-octyl thiophene), thus reflecting a behaviour comparable to that of metals or graphite. In the case of polypyrrole, it was found that the dispersive and acid–base properties are correlated, and that the high energetic sites are predominantly acidic. Ageing and low doping levels have a significant impact on polypyrrole surface thermodynamics as they resulted in low surface energy and acidity of this ICP.

DNA adsorption onto conducting polypyrrole

Abstract Deoxyribonucleic acid (DNA) adsorption onto chemically synthesized polypyrrole powders was investigated as a function of pH, buffer nature, ionic strength and substrate nature. DNA adsorption was found to be in the range of 0.13–0.55 mg m −2 for the conditions under investigation. Strong DNA adsorption was obtained at low pH and high ionic strength. The decreasing order of adsorption as a function of the native dopant was nitrate, chloride>sulfate. The isotherms were found to be of the Langmuir type or sigmoid, depending on the combination of (at least) substrate and buffer natures. Affinity constants determined using Scatchard and Hill plots were found to be as high as 10 6 M −1 .

Evidence of specific interaction between γ-glycidoxypropyltrimethoxysilane and oxidized aluminium using high-mass resolution ToF-SIMS†

High mass resolution time-of-flight secondary ion mass spectroscopy (ToF-SIMS) has been employed to study the interaction between oxidized aluminium and hydrolysed γ-glycidoxypropyltrimethoxysilane (GPS). The process used to prepare the specimens was similar to that used in the aerospace industry. Fragments present at nominal mass m/z = 71 were examined carefully. The high mass resolution allowed us to show the presence of AlOSi+ fragment of nominal mass 71 and exact mass 70.9534. Its presence demonstrates the formation of a covalent bond between aluminium and GPS. This result is also enhanced by the detection of another feature in the mass spectra assigned to a fragment of structure AlOSi+ = CH2 detected at a nominal mass of m/z = 85. Depth profiles of these ions were obtained using the primary ion beam in continuous mode to perform gentle etching of the surface. It is shown that the AlOSi+ is the only fragment that is retained at mass 71. The other, organic, features are quickly removed. This is to be expected when profiling through an interfacial layer where this type of specific interaction is present. Copyright

Characterization of conducting polymers by inverse gas chromatography Part II. Effect of dopant on the dispersive and specific properties of polypyrrole

Abstract A series of polypyrroles, synthesized using iron(III) oxidizing agent, was characterized by inverse gas chromatography (IGC). The dispersive component to the surface tension of these materials falls in the range 40–60 mJ/m 2 for Cl − - and NO 3 − -doped polypyrroles, whereas that of Fe(CN) 6 − is extremely high (106 mJ/m 2 ) when compared to a conventional polymer. These values rank conducting polypyrroles between conventional insulating polymers and high surface energy materials such as metals, metal oxides and graphite. In addition, all polymers exhibit strong specific adsorption of acidic and basic molecular probes, confirming the Lewis amphoteric behaviour of conducting polypyrroles. The hard and soft acids and bases (HSAB) concept is also emphasized in an original manner based on acidic and basic Lewis probes and in connection with the nature of the dopant. This IGC study shows that the dopant plays an important role in the surface thermodynamics of conducting polypyroles, as evidenced by the magnitude of the dispersive and acid-base properties.

Impact of water quality on removal of carbamazepine in natural waters by N-doped TiO2 photo-catalytic thin film surfaces

Photocatalytic experiments on the pharmaceutical pollutant carbamazepine (CBZ) were conducted using sol-gel nitrogen-doped TiO(2)-coated glass slides under a solar simulator. CBZ was stable to photodegradation under direct solar irradiation. No CBZ sorption to the catalyst surface was observed, as further confirmed by surface characterization using X-ray photoelectron spectroscopic analysis of N-doped TiO(2) surfaces. When exposing the catalyst surface to natural organic matter (NOM), an excess amount of carbon was detected relative to controls, which is consistent with NOM remaining on the catalyst surface. The catalyst surface charge was negative at pH values from 4 to 10 and decreased with increasing pH, correlated with enhanced CBZ removal with increasing medium pH in the range of 5-9. A dissolved organic carbon concentration of 5mg/L resulted in ~20% reduction in CBZ removal, probably due to competitive inhibition of the photocatalytic degradation of CBZ. At alkalinity values corresponding to CaCO(3) addition at 100mg/L, an over 40% decrease in CBZ removal was observed. A 35% reduction in CBZ occurred in the presence of surface water compared to complete suppression of the photocatalytic process in wastewater effluent.

The interaction of a commercial dry film adhesive with aluminium and organosilane treated aluminium surfaces: a study by XPS and ToF-SIMS

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.

An inverse gas chromatographic study of the PMMA / conducting polypyrrole interface

The poly(methyl methacrylate)/chloride-doped polypyrrole (PMMA/PPyCl) interface in PMMA-coated PPyCl powders has been characterized by inverse gas chromatography (IGC). The study is based on the determination of the surface energy of the various materials tested. It is shown that γd s, the dispersive contribution to the surface energy of PPyCl, decreases following adsorption of PMMA onto PPyCl, a high surface energy material. The overall acid-base character of the coated powders shifts from a predominant acidity to a predominant basicity following PMMA adsorption. However, the nature of the casting solvent strongly influences the morphology of the PMMA coatings, as judged from their surface thermodynamic properties. Indeed, for approximately the same relative surface proportion of PMMA, both dispersive and acid-base properties of the coated PPyCl differ, depending on whether PMMA is cast from a good or a poor solvent. The results obtained suggest that from poor solvents, PMMA adsorbs onto PPyCl and leads ...

Segregation and crosslinking in urea formaldehyde/epoxy resins: a study by high-resolution XPS

Abstract The segregation of minor components such as flow agents, in an industrial coil coating based on epoxy resins crosslinked with a urea formaldehyde resin and applied to a hot-dipped galvanized steel (HDGS) substrate, has been investigated by high resolution XPS. The addition of a low amount of flow agent in the coating formulation leads to changes in the surface elemental composition. High-resolution monochromated XPS C1s spectra can be peak-fitted taking into account all functionalities of the respective components of the formulation. The examination of both the elemental and chemical surface compositions clearly demonstrates that the use of flow agent in the process leads to its preferential segregation towards the air–film interface. This result is interpreted in terms of minimisation of the surface free energy of the final coil coating. It is also possible to monitor the extent of crosslinking undergone within the coil coating system, using the peak-fitting in the same manner as above, and it was concluded that the system is fully crosslinked.

THE INFLUENCE OF PROCESS PARAMETERS ON THE INTERFACIAL CHEMISTRY OF γ-GPS ON ALUMINIUM: A REVIEW

Within the “International Collaborative Programme on Organosilane Adhesion Promoters” (ICOSAP), scientists from the U.S. and Europe contributed to the understanding of an organosilane primer process, based on an aqueous solution of γ-glycidoxypropyl trimethoxysilane (γ-GPS), used currently for aerospace repair purposes. Parameters such as temperature of cure, ageing time, and concentration of the aqueous solution have been investigated, and this work reviews the effect that each variable has on the process, and the resulting integrity of the GPS/aluminium interface. The aim of the work was to provide a more environmentally friendly replacement for pretreatments containing Cr(VI) that are currently used, such as chromic acid anodising and acid etching employed for the structural adhesive bonding of aluminium. The formation of covalent interfacial bonding is shown to be a function of the hydrolysis and condensation of the silane molecules in solution as well as the type of solvent used. The curing temperature of the aqueous film on the aluminium is also shown to have an effect on the chemistry of the resulting primer film and its efficacy as an adhesion promoter. All these parameters must be optimised to obtain durability that matches that obtained by a phosphoric acid anodising pretreatment. This work reports on the various studies performed towards this aim carried out within the remit of the ICOSAP initiative, with a particular emphasis on the interfacial chemistry between γ-GPS and the aluminium substrate, and indicates the manner in which the results point the way towards a viable, environmentally friendly pretreatment for the adhesive bonding of aluminium for aerospaceapplications.

Adsorption of poly(methyl methacrylate) and poly(vinyl chloride) blends onto polypyrrole. Study by X-ray photoelectron spectroscopy, time-of-flight static secondary ion mass spectroscopy, and inverse gas chromatography.

Poly(vinyl chloride) (PVC) and poly(methyl methacrylate) (PMMA) were co-adsorbed onto conducting, nitrate-doped, polypyrrole (PPyNO3) from tetrahydrofuran and 1,4-dioxane. The surface composition of PPyNO3 before and following polymer adsorption was monitored by X-ray photoelectron spectroscopy and time-of-flight static secondary ion mass spectroscopy which indicated that PMMA and PVC co-adsorb. However, PVC adsorption is substantially higher from 1,4-dioxane, hence a solvent effect. Inverse gas chromatography permitted to determine the dispersive contribution to the surface energy (gamma(s)d) and acid-base descriptors of the untreated and polymer blend-coated polypyrrole specimens. Whilst gamma(s)d values clearly indicate that the polymer coatings are patchy, acid-base descriptors suggest that the blend patches have a PMMA-rich surface, especially in the case of adsorption from 1,4-dioxane.