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ABSTRACT: Polymer materials degradation is a well-known limitation to their characterization in SEM. In this paper authors present an additional possibility for polymer imaging offered by the Environmental SEM applied to the PMMA with micrometric relief. As shown by the so-called double-scan procedure, increasing the pressure enables to delay the degradation of the polymer surface. To evaluate quantitatively this observation, the classical formula to calculate the electron dose is adapted to ESEM characteristic. It is shown first that pressure enables to decrease the electron dose and all that takes place as if the skirt electrons do not participate in the irradiation. Secondly this procedure allows to obtain the critical dose of topographic degradation, applied to the PMMA with micrometric relief D(C) was found to be 1.31±0.28Cm(-2). Finally it becomes then possible, knowing the D(C) for a given sample, to evaluate the limit of investigation without topographic surface degradation: for example, the maximal field of view (linked to the magnification) depending on the other parameters.
Ultramicroscopy 07/2012; 122C:32-36. · 2.47 Impact Factor
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ABSTRACT: Dopamine-melanin films produced through the oxidation of dopamine in the presence of oxygen as an oxidant allow to reduce silver ions onto silver particles as already described in the paper by Lee et al. (H. Lee, S.M. Dellatore, W.M. Miller, P.B. Messersmith, Science 318 (2007) 426.). This reduction process has to occur through the oxidation of moieties present in the melanin film. This investigation shows that the free radicals present in the pseudomelanin film, quantified by means of electron spin resonance spectroscopy (ESR) for the first time, are not used in the transformation of Ag(+) cations to deposit silver. The ESR signal is hardly affected by the deposition of silver particles. On the other hand, X-ray photoelectron spectroscopy shows a small increase in the density of quinone groups and a small decrease of catechol groups on the surface of the film during the deposition of silver. This suggests that the deposited pseudomelanin films contain a significant fraction of catechol groups able to trigger reduction processes of metallic cations. These silver nanoparticles remain adherent to the melanin films and allow for a quantitative killing of Escherichia coli over a broad range of bacterial dilutions. However, the presence of the bacteria induces a release of the nanoparticles. The pseudomelanin films cannot be reused again for a silver ion reduction step. Nevertheless, the easy preparation of the pseudomelanin-silver composite and its effective one shot bacterial killing activity renders the strategy presented in this paper attractive. Some fundamental questions about redox process allowed by the pseudomelanin films will also be asked.
Journal of Colloid and Interface Science 09/2011; 364(2):359-65. · 3.07 Impact Factor
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ABSTRACT: Gas impact on the EDS profile resolution at the interface of composite interface resin/Al was investigated with two gaseous environments: helium and water vapor. Two main components of the global profile at the interface were investigated: the contrast of the profile and the spatial resolution. A complementary approach was developed by comparing gas nature impact versus the pressure and versus the scattering regime. The results show that the unscattered electron beam mainly governs EDS profile spatial resolution as long as the scattering regime is single or oligo scattering. Then for plural scattering, spatial resolution is dramatically degraded. In addition, the contrast is degraded since a gas is introduced, whatever the gas, the pressure and so the scattering regime. This approach would enable to better understand the respective contributions of the unscattered beam and the skirt and the influence of the gases nature on them.
Micron 06/2011; 42(8):877-83. · 1.53 Impact Factor
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ABSTRACT: The incorporation of two different copper (II) phtalocyanines differing in their charged groups (sulfonato versus pyridino) in exponentially growing polyelectrolyte multilayer films (PEMs) made either from poly-l-lysine (PLL) and poly-l-glutamic acid (PGA) or from PLL and sodium hyaluronate (HA) has been investigated. The motivation of our study was to investigate the influence of different parameters on the ability of a molecule of constant size but differing in its charge to incorporate in and to be released from PEMs. The investigated parameters were: the nature of the last deposited polyelectrolyte, the ionic strength of the solution, and the nature of the polyanion present in the film (PGA versus HA). Complementarily, we have investigated the simultaneous or the consecutive incorporation of two anionic species, the anionic phtalocyanine and Ti(IV) (bislactato dihydroxyde) in (PLL−HA)n films: the incorporation of both species was possible only if they were put in competition during their incorporation in the film, but if the films were saturated by one of the species, the subsequent incorporation of the second one was not possible anymore. Overall our findings show that exponentially growing PEMs having a positive Donnan potential can be used to incorporate negatively charged copper phtalocyanines at very high concentrations, whereas the positively charged counterparts are totally excluded. In addition, our data show that the negatively charged phtalocyanines are not homogeneously incorporated through the whole thickness of the PEMs.
04/2011;
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ABSTRACT: The concept of reactive layer-by-layer (LBL) deposition allows the build-up of films containing polycations and oxide particles, namely, silica and poorly crystalline anatase. Because polyelectrolyte multilayer films have been produced from blended polyanions or polycations solutions and since preferential incorporation of one of the partners of the blend has been found in most cases, one should wonder if a preferential polycondensation of either silica or titania should occur when the reactive deposition is performed from a solution containing a precursor of both inorganic species. X-ray photoelectron (XPS) and UV-visible spectroscopies show that the reactive LBL films made from the blend and poly(diallyldimethylammonium chloride) (PDADMAC) incorporate predominantly silica over TiO(2) over the whole molar fraction range of the silicic acic/hydrosoluble Ti(IV) complex. The transparency of the films below 365 nm, corresponding to the band edge of TiO(2), can easily be modulated. The silica/TiO(2) films are all able to bind hexacyanoferrate owing to the presence of the polycation allowing the binding of the oxide particles to the substrate. However, the binding capacity of the film does not scale proportionally to its thickness. The films made from eight dipping cycles showed a sudden decrease in their binding capacity for hexacyanoferrate when the molar fraction of the titanium complex was higher than ∼0.6 in the blend. For the same films, electrochemical impedance spectra (EIS) showed marked differences with a change in film composition: the more TiO(2) in the film, the higher the resistance to electron and to mass transfer. Therefore, EIS helps to explain the reduced surface concentration measured by means of cyclic voltammetry for films rich in TiO(2).
Langmuir 03/2011; 27(5):1859-66. · 4.19 Impact Factor
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ABSTRACT: Amperometric biosensors are widely used for clinical, food industry and environmental control. A universal platform allowing
immobilization of different enzymes could provide a fast and easy way to design new sensors, but the main drawback effect
with oxidase based biosensors is the production of hydrogen peroxide. The direct electron transfer is a way to limit the H2O2 production. A modified electrode described by Zhao et al. (Bioelectrochemistry, 69(2):158, 2006), based on immobilization of glucose oxidase/colloidal gold nanoparticles on a glassy carbon electrode by Nafion film, has
been used. Its sensitivity is 0.4μA mM−1 cm−2, reproducibility is 3.0%, detection limit is 0.37mM, response to glucose is linear up to 20mM; limit of detection is 0.37mM
and response time is about 1.5min. This sensor displays a formal redox potential compatible with a direct electron transfer,
and has been tested for its response in time and GOx denaturation by X-ray photoelectron spectroscopy. Vanishing of disulphide
bonds of GOx has been observed after a period in a saturating solution of glucose but this does not appear determinant in
loss of enzyme activity.
Microchimica Acta 09/2008; 163(3):211-217. · 3.03 Impact Factor
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ABSTRACT: The aim of this work is to introduce the use of low vacuum scanning electron microscopy (LVSEM) coupled with an X-ray energy dispersive spectrometer (EDS) in the field of structural adhesives, more precisely aluminium/epoxy resin assembly. Such assembly is characterized by the creation of an interphase resulting from the metal diffusion inside the resin during cross-linking. As the performance of the final bond is strongly links by the interphase properties, fine characterization of this interphase, in particularity the evaluation of its thickness is essential to understand the macroscopic properties of the adhesive assembly. First, the EDS acquisition parameters were investigated in order to limit the sample/resin damage/degradation due to the incident electrons beam irradiation. Then a specific methodology of stacked profiles was defined to improve the precision of the measures. To evaluate the true Al diffusion profile, the impact of the interaction volume of incident electron in the material on the Al signal variation during the interface crossing was calculated and the effect of the gas pressure on the electron beam characteristic and so on the measured profiles was examinated.According to our developed methodology and data treatments, Al diffusion profile was interpreted and interphase thickness was qualitatively determined by comparison with an experimental baseline. This innovative methodology promotes the use of LVSEM–EDS in the field of adhesive structural assemblies, but also, deals with a comparative study on the effect of the gas pressure on the EDS profile analysis.
Micron.
