Christian Perruchot

Preparation and characterisation of gold nanoparticle assemblies on silanised glass plates

Abstract Gold nanoparticles were prepared by the chemical reduction of AuCl 4 − and attached to aminopropyltrimethoxysilane-treated glass plates. The assemblies of gold nanoparticles on silanised glass were characterised by UV spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and surface-enhanced Raman scattering (SERS). The gold nanoparticles had a diameter in the range 40±10 nm as estimated by AFM. Gold was found to be in the metallic state as judged from XPS measurements of the Au 4f 7/2 core electron binding energy. AFM showed that the gold nanoparticles experience a self-organisation on the silanised surface in such a way that the final assemblies have a certain degree of roughness and compactness. These characteristics are intimately related to the SERS effect as determined using the molecular probe bi-ethylene-pyridine at very low concentration. A huge enhancement of the Raman signals was observed and assigned to a coupling between gold particles. However, this SERS effect critically depends on the surface treatment of the substrate by the silane coupling agent, a procedure that is necessary for the attachment of the gold nanoparticles.

Synthesis and aqueous solution properties of polyelectrolyte-grafted silica particles prepared by surface-initiated atom transfer radical polymerization

A range of polyelectrolyte-grafted silica particles have been prepared by grafting suitable initiators onto near-monodisperse, 304-nm-diameter silica particles using siloxane chemistry, followed by surface-initiated atom transfer radical polymerization (ATRP) of four ionic vinyl monomers, namely sodium 4-styrenesulfonate (SStNa), sodium 4-vinylbenzoate (NaVBA), 2-(dimethylamino)ethyl methacrylate (DAM), and 2-(diethylamino)ethyl methacrylate (DEA) in protic media. The resulting polyelectrolyte-grafted silica particles were characterized using dynamic light scattering (DLS), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), helium pycnometry, and diffuse reflectance infrared Fourier transfer spectroscopy (DRIFTS). The TGA results indicated that the polyelectrolyte contents of the silica particles could be varied from 0.6% to 6.0% in weight. SEM studies revealed several surface morphologies for the grafted polyelectrolytes and XPS analysis of the particle surface also provided good evidence for surface grafting. Combined aqueous electrophoresis and DLS studies confirmed that these polyelectrolyte-grafted silica particles had pH-dependent colloid stabilities, as expected. Cationic polyelectrolyte-grafted silica particles were colloidally stable at low or neutral pH, but became aggregated at high pH. Conversely, anionic polyelectrolyte-coated silica particles became unstable at low pH. It was found that the rate of surface-initiated ATRP was substantially slower than the analogous solution polymerization. Finally, there was some evidence to suggest that, at least in some cases, a significant fraction of polymer chains became detached from the silica particles during polymerization.

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.

The surface chemistry and acid–base properties of a PAN-based carbon fibre

Akzo Tenax HTA carbon fibres (high strength) with progressive amounts of the standard commercial treatment have been investigated using a number of surface analytical methods. Chemical content and structure have been interrogated by XPS and ToF-SIMS, and compared to thermodynamic and acid–base properties probed by IGC and DCAA. The γsd values of the fibres were calculated at ca. 50°C and were found to decrease from 104 mJ m−2 for untreated fibres to 78 mJ m−2 for 200% oxidised fibres. The acid–base character at the molecular level and the macroscopic properties of γsp are significantly enhanced even at low levels of oxidation, resulting in increased wettability of carbon fibres by polar species. Wettability of the surface by non-polar species appears to be largely unaffected by oxidation. XPS analysis reveals that oxygen is introduced progressively at the expense of carbon content, and trace amounts of Na and Cl slowly increase with oxidation. ToF-SIMS shows that the amount of Ca and Na increases very quickly during the early stages of oxidation, whereas Cl and O increase at a more steady rate.

Use of aminosilane coupling agent in the synthesis of conducting, hybrid polypyrrole–silica gel particles

A new route for the synthesis of conducting polypyrrole–silica composites is described. Silica gel particles were modified by aminopropyltriethoxysilane (APS) and acted as porous inorganic substrates for the in situ synthesis of polypyrrole (PPy). The resulting polypyrrole–silica–APS hybrid materials were characterized by XPS, thermogravimetric analysis, BET and conductivity measurements. It is found that APS yields a substantial increase in the PPy mass loading (from 6 to 11.5 wt.%) but, more importantly, the hybrid particles obtained are conductive and have a negligible static charge in XPS due to their PPy-rich surfaces. In the absence of any APS treatment, polypyrrole is mainly loaded in the pores of the silica gel so these polypyrrole–silica particles are poorly conductive and charge up during XPS analysis. The conductivity threshold (10−2 S cm−1) was obtained for an APS initial concentration of 1% (v/v). In addition, these conducting hybrid particles have a fairly high specific surface area in the 160–180 m2 g−1 range.

Impact ionization experiments with low density conducting polymer-based micro-projectiles as analogues of solar system dusts

Abstract Results for electrostatic acceleration of organic, silica- and metal-based micro-projectiles ( μm diameter) are presented. These micro-projectiles, which are mimics for cosmic dust, are accelerated by using a conducting polymer (polypyrrole or polyaniline) to provide a thin electrically conductive overlayer on core particles (polystyrene latex or poly(4-bromostyrene) latex), or by the in situ polymerization of pyrrole in the presence of an ultrafine silica sol (or tin(IV) oxide) to produce polypyrrole–silica (or polypyrrole–tin(IV) oxide) nanocomposite particles. In addition, sterically stabilized polypyrrole particles were also examined. The particles can be charged and electrostatically accelerated to hypervelocities (up to 38 km s −1 ) using a Van de Graaf accelerator. The ionization resulting from their impacts on metal targets (copper, rhodium or gold) was measured. It was found that, for impacts on a given target, the various organic-based and organic–inorganic hybrid dusts had similar ionization yields when normalized to particle mass. However, it was only at high impact speeds (greater than 10 km s −1 ) that this yield was similar to that from impacts of iron particles. At lower speeds the organic-based and organic–inorganic hybrid particles have ionization yields for impacts on copper that exceeded that of iron by a factor of three at 5 km s −1 and by a factor of ten at 1 km s −1 . This behaviour was dependent on the nature of the metal target (with a smaller difference for impacts on gold and rhodium). Furthermore, it was found that for some metal targets (gold and rhodium) there was little difference in ionization yield between the targets. The relatively easy synthesis of this wide range of conducting polymer-based micro-particles strongly indicates their suitability as mimics of solar system dusts for the calibration of impact ionization detectors for spacecraft.

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.

SIMS analysis of conducting polypyrrole–silica gel composites

Abstract Secondary ion mass spectrometry (SIMS) has been used to characterize novel hybrid conducting polypyrrole–silica gel composites. The silica gel particles act as a high surface inorganic substrate for the in situ chemical synthesis of polypyrrole (PPy) in aqueous media. However, the conventional method using untreated silica gel as a host material for pyrrole polymerisation led to insulating PPy–silica composites, which exhibit a silica-rich surface. By contrast, pre-treatment of the silica gel particles by aminopropyltriethoxysilane (APS) prior to polymerisation results in conducting PPy–APS–silica composites, the surface of which was found to be PPy-rich. The present study uses the unique capabilities of SIMS to distinguish unambiguously between fragments from the silane coupling agent and the conducting PPy overlayers. Specific negative ions from PPy and the underlying substrate particles were effective in monitoring the change in the PPy content at the surface of the composites vs. the initial concentration of APS used to pre-treat silica gel particles. This SIMS analysis clearly demonstrated that APS is effective in increasing the surface PPy content and thus confirms previously published XPS data based on some necessary assumptions.

The role of a silane coupling agent in the synthesis of hybrid polypyrrole–silica gel conducting particles

The preparation of new hybrid conducting polymer–silica gel particles is described. The silica gel acts as a high surface area substrate (431 m2 g–1) for the in situchemical synthesis of conducting polypyrrole in aqueous solution in order to obtain hybrid polypyrrole–silica particles. The role of a common silane coupling agent (i.e. aminopropyltriethoxysilane, APS) in the pretreatment of silica gel prior to polymerization and preparation of polypyrrole–APS–silica particles is also investigated. It was found by TGA that the polypyrrole mass loading is higher in polypyrrole–APS–silica than in polypyrrole–silica particles. XPS results indicated that APS-treated silica leads to polypyrrole-rich surface particles not found with the untreated silica. Consequently, the polypyrrole–APS–silica pellets were three orders of magnitude more conductive than those of polypyrrole–silica.The surface area of the polypyrrole–silica (422 m2 g–1), as measured by BET, matched that of the untreated silica whilst that of the polypyrrole–APS–silica (162–184 m2 g–1) is significantly lower. The combination of XPS, TGA, BET and conductivity measurements suggest that pyrrole is predominantly polymerized in the pores of the untreated silica gel whilst the APS pretreatment of silica leads to the formation of a thin overlayer of polypyrrole at the surface of the silica gel in addition to a higher conducting polymer loading in the gel pores.

The Role of a Silane Coupling Agent in the Preparation of Novel Hybrid Polypyrrole-Silica Particles.

Abstract The preparation of hybrid polypyrrole-silica gel particles is well documented. The silica gel acts as a porous-high-surface-area substrate for the in-situ chemical synthesis of conducting polypyrrole in aqueous media. However, the surface of such materials is silica-rich as found by XPS. In order to obtain similar hybrid particles with, instead, a polypyrrole-rich surface, we pretreated the silica gel particles with a silane coupling agent (ie aminopropyltriethoxysilane, APS) prior to polypyrrole (PPy) coating. This led to the synthesis of novel hybrid PPy-silica-APS materials which were characterized by TGA, elemental analysis. XPS, SIMS, BET and conductivity measurements. These novel hybrid particles have higher PPy loadings, exhibit a high specific surface area with a PPy-rich surface, and are three orders of magnitude more conductive than the particles prepared without APS pretreatment.