Fabienne Poncin-Epaillard

Polyaniline as a new sensitive layer for gas sensors

The different synthesis routes and deposition methods of polyaniline (PANi) as sensitive layer, as well as the various techniques to monitor the gas adsorption on polyaniline are reviewed. Finally, the deposition of polyaniline onto silicon as transducer or substrate is discussed. The literature reviewed based on a 7-year-period, since 1995, shows a great interest to study the polyaniline/gas interface properties.

In situ spectroellipsometry study of the crosslinking of polypropylene by an argon plasma

The exposure of polypropylene to an argon plasma is studied by in situ spectroscopic ellipsometry in the UV-visible and in the IR range. The results are correlated with amorphous phase extraction and proton nuclear magnetic resonance (NMR) analysis. UV-visible real-time ellipsometry reveals the formation of an overlayer with higher refractive index, which is attributed to a densification of the polymer, and thus to crosslinking at the surface. This assumption is confirmed by the decrease in the extracted mass after treatment. The crosslinking mechanism involves the elimination of methyl groups, and also the formation of exomethylenic bonds, as shown by NMR and IR ellipsometry. Spectroscopic ellipsometry appears as a valuable tool to study the interaction between a plasma and a polymer, as UV-visible ellipsometry is sensitive to structural changes in the polymer, while IR ellipsometry can detect the appearance and disappearance of chemical groups in a surface layer.

Characterization of CO2 plasma-treated polyethylene surface bearing carboxylic groups

Abstract The surface modification of high density polyethylene by a CO2 microwave plasma is described with the aim of fixing carboxylic groups. The characterization is discussed in terms of functionalization, degradation, crystallization and cross-linking. The formation of carboxylic acids seems mainly favored by the presence of the CO2 active species. The degradation leading via chain scissions to the formation of volatile byproducts is shown to be heterogeneous by mainly affecting amorphous zones. The structural modification is associated with a twisting motion of macromolecular chains having defects to more organized conformations. Finally, cross-linking appears weak due to the absence of chromophoric sites and of VUV radiations in the plasma.

Cold plasma surface modification of conventionally and nonconventionally plasticized poly(vinyl chloride)-based flexible films : Global and specific migration of additives into isooctane

The effect of plasma-induced surface crosslinking of poly(vinyl chloride) (PVC)-based flexible films was investigated to limit its migration from packaging into fatty foodstuffs. The global migration was monitored by immersion into isooctane and the specific migrations of di-2-ethylhexyladipate (DEHA) and epoxidized soybean oil (ESO) were monitored by supercritical fluid chromatography analysis of the resulting isooctane solution. The plasma induced modifications were monitored with respect to the surface energy, weight loss, and surface crosslinking. The global migration from conventionally plasticized film, whose composition corresponds to an ordinarily used formulation for the manufacture of PVC wrap films, was controlled by different plasma treatments and the best results were obtained with Ar plasma. Further decreases in global migration were obtained by treating permanently plasticized films containing an elastomeric ethylene-based terpolymer (EE) in complete or partial replacement of DEHA. Before treatment, the replacement of DEHA with EE increased the DEHA and ESO specific migrations. Argon plasma treatment of permanently plasticized films led to samples that did not exhibit any migration.

Adhesion mechanisms of silica layers on plasma-treated polymers. Part I. Polycarbonate

We have studied the influence of plasma treatment in various gases (Ar, NH3, N2) on the surface modification of polycarbonate (PC) and on the adhesion of plasma-deposited silica layers to PC. Surface modification was investigated using in situ IR ellipsometry, X-ray photoelectron spectroscopy, and contact angle measurements interpreted in terms of electron-acceptor/ donor groups. In addition, in situ UV-visible ellipsometry enabled crosslinking analysis. Due to UV photon emission, Ar plasma treatment induced crosslinking as well as photo-Fries rearrangements and related reactions, thus creating phenolic groups. These groups are acidic sites and are likely to react with the electronegative oxygen atoms of silica. Adhesion of silica to PC, as measured by the micro-scratch test, was enhanced by Ar plasma treatment. The improvement is attributed to the crosslinking of PC, on the one hand, and to acid-base interactions and/or covalent bonding between PC and silica, on the other hand. A further improvement in a...

Relationship between ammonia sensing properties of polyaniline nanostructures and their deposition and synthesis methods

The ammonia absorption properties of polyaniline nanostructures are studied in terms of sensitivity, response and recovery times and stability. These characteristics are obtained by measuring, at room temperature, the absorbance variations at 632 nm. The nanostructures are synthesized either by interfacial or rapid or dropwise polymerizations with the oxidant-to-monomer mole ratio equals to 0.5 or 1. The influence of the deposition method (in-situ or drop-coating technique) as well as the nature of the dopant (HCl, CSA or I(2)) on the gas detection properties are also studied. The results show a strong dependence of the morphology on the deposition method, the in-situ technique leads to the best sensitivity and response time. For this deposition method, the nanostructures sensitivity, response time and regeneration rate depend on the synthesis method, the dopant and the mole ratio. The ageing effect after 8 months under ambient conditions and the mechanism of interaction between the polyaniline nanostructures and ammonia molecules are also presented.

Characterization of polypropylene surface treated in a CO2 plasma

The polypropylene modification in CO2 plasma mainly contributes to degradation, functionalization, and cross-linking. The degradation, whose rate is depending on CO2 dissociation and oxygen atom formation, is a quite slow reaction and it is associated with surface topography alteration, especially of the amorphous phase of the polypropylene. The surface roughness increases with the treatment duration and the amorphous phase is more degraded than the crystallized part. The functionalization, corresponding to an increase of the surface energy (57.3 mJċ m− 2 in 30 s), and to an oxidation (23 oxygen at.%) with the appearance of alcohol, ketone, and acid functions is a much faster phenomenon. Cross-linking takes also place during this type of treatment and will reinforce the stability of the modified surface.

Argon plasma treatment of polycarbonate: In situ spectroellipsometry study and polymer characterizations

The influence of argon plasma on polycarbonate (PC) was studied in terms of structural changes, reaction mechanisms, and adhesion. In situ ultraviolet‐visible ellipsometry reveals formation of a surface layer with a higher refractive index than the untreated polymer. The increase in the refractive index is attributed to polymer densification, which in turn is attributed to crosslinking. However a decrease in the average molecular weight is also observed, and two populations of macromolecules of different sizes are detected by light scattering measurements, revealing a competition between crosslinking and degradation. The reaction mechanisms are investigated using nuclear magnetic resonance and in situ infrared ellipsometry. Degradation is caused by carbonate bond breaking, whereas crosslinking seems to be related to a decrease in methyl groups. In addition, an increase in surface acidity is detected by contact angle measurements and is attributed to photo‐Fries rearrangements producing phenolic groups. Th...

Reactivity of a polypropylene surface modified in a nitrogen plasma

The modification of a polypropylene surface in a nitrogen plasma is studied in terms of degradation, crosslinking, functionalization, and activation (radical site creation.) The most important reactions are functionalization through primary amine formation and radical creation through methyl-group elimination. Degradation and crosslinking are competitive and the latter is more important when the plasma conditions (exposure time, discharge power) are severe. Exomethylenic bonds (CH2=C) are formed preferentially over crosslinking reactions. Chemical titrations are described for radical and amine concentrations on the polypropylene surface.

Elaboration of highly hydrophobic polymeric surface--a potential strategy to reduce the adhesion of pathogenic bacteria?

Different polymeric surfaces have been modified in order to reach a high hydrophobic character, indeed the superhydrophobicity property. For this purpose, polypropylene and polystyrene have been treated by RF or μwaves CF4 plasma with different volumes, the results were compared according to the density of injected power. The effect of pretreatment such as mechanical abrasion or plasma activation was also studied. The modified surfaces were shown as hydrophobic, or even superhydrophobic depending of defects density. They were characterized by measurement of wettability and roughness at different scales, i.e. macroscopic, mesoscopic and atomic. It has been shown that a homogeneous surface at the macroscopic scale could be heterogeneous at lower mesoscopic scale. This was associated with the crystallinity of the material. The bioadhesion tests were performed with Gram positive and negative pathogenic strains: Listeria monocytogenes, Pseudomonas aeruginosa and Hafnia alvei. They have demonstrated an antibacterial efficiency of very hydrophobic and amorphous PS treated for all strains tested and a strain-dependent efficiency with modified PP surface being very heterogeneous at the mesoscopic scale. Thus, these biological results pointed out not only the respective role of the surface chemistry and topography in bacterial adhesion, but also the dependence on the peaks and valley distribution at bacteria dimension scale.