Fabrice Lallemand

Ammonia gas sensor based on electrosynthesized polypyrrole films.

In this work, design and fabrication of micro-gas-sensors, polymerization and deposition of poly(pyrrole) thin films as sensitive layer for the micro-gas-sensors by electrochemical processing, and characterization of the polymer films by FTIR, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), are reported. The change in conductance of thin polymer layers is used as a sensor signal. The behaviours, including sensitivity, reproducibility and reversibility, to various ammonia gas concentrations ranging from 8 ppm to 1000 ppm are investigated. The influence of the temperature on the electrical response of the sensors is also studied. The experimental results show that these ammonia gas sensors are efficient since they are sensitive to ammonia, reversible and reproducible at room temperature.

Influence of sodium saccharin on the electrodeposition and characterization of CoFe magnetic film

Abstract The corrosion resistance of magnetic film is a significant property which has to be considered in the magnetic head manufacture. Deposits of cobalt–iron alloy were obtained from a sulfate bath at pH 3, on copper cathodes, using direct current. In the present work, the corrosion behavior of electrodeposited CoFe film was investigated in the presence of organic additives in the electrolysis bath: sodium saccharin. Indeed, sodium saccharin salt was more soluble than saccharin. The changes in the concentration of organic additive in CoFe bath during electroforming were examined. The deposit morphology was determined by SEM observations. The main results are that the presence of sodium saccharin alters the deposit corrosion resistance properties.

Effect of ultrasounds on the electrochemical synthesis of polypyrrole, application to the adhesion and growth of biological cells.

In this study, a new way to synthesize polypyrrole films is presented. This original way consists in the electropolymerization of polypyrrole under high frequency ultrasonic irradiation on conductive fluorine-doped tin oxide surfaces. The polypyrrole films obtained are then compared, in terms of chemical structure and morphology, to polypyrrole films synthesized by standard electrochemical methodology. Next, these polymer films are tested as an alternative to biomaterials that are commonly used as cell culture substrates. Thus, the adhesion and growth of osteoblastics cells and microbial cells on polymer-modified surfaces are investigated by using qualitative observation and quantitative tests. These studies proved the non-toxicity of the polymer films for osteoblastic and microbial cells but also a different behaviour of osteoblastic cells and microbial cells with polypyrrole films.

Effects of the structure of organic additives in the electrochemical preparation and characterization of CoFe film

Abstract The use of organic additives is widespread in the manufacturing of thin films by electrochemical deposition. Common additives like saccharin (SAC) were used as leveling and brightening agents in the cobalt–iron deposits. In the present work, effects of additives molecular structure on the CoFe deposits from sulfate electrolytes at pH 3 were investigated. Phthalimide (PHTA) and a new additive (OAS) were tested like organic additives to understand the influence of different functional groups of these compounds. The composition and the morphology of the binary alloy were examined by SEM. The corrosion properties were characterized by voltammetry. The main results revealed that the presence of the sulfonamide in the structure of organic additives does not play the role in brightening and leveling agent, but this function seems to be important for CoFe deposit corrosion resistance even if all additives change the deposit corrosion resistance properties. Moreover, the complexation between the iron ion and the organic additive seems to be affected by the presence of the carbonyl group.

Kinetic and morphological investigation of CoFe alloy electrodeposition in the presence of organic additives

Abstract The use of organic additives is widespread in the manufacturing of thin films using electrodeposition. Common additives like saccharin (SAC) are used as leveling and brightening agents. In the present work, a comparative study of the influence of organic additives containing a similar saccharin molecular structure on CoFe alloy electrodeposition has been performed in order to obtain information about the kinetics of the cathodic process and the morphology of the deposits. The study was based on an electrochemical investigation using steady-state polarization measurements, coupled with scanning electron microscopy and X-ray dispersive analysis of the CoFe deposits. The composition, the current efficiency and the partial current densities of the CoFe alloy were determined in order to study the influence of SAC, phthalimide (PHTA) and another additive containing sulfur element: o -toluene sulfonamide ( o TOL) on the CoFe deposition from sulfate and chloride electrolytes at pH 3. Experimental results indicate that saccharin influence strongly the electrode kinetic contrary to o TOL and PHTA. The morphology of the CoFe deposits depends on used organic additive. It was also noted that the presence of saccharin results in smoother, more compact and more leveled deposits as compared to PHTA or o TOL.

Doping properties of PEDOT films electrosynthesized under high frequency ultrasound irradiation.

The present study presents the use of high frequency ultrasound (500 kHz, 25 W) for 3,4-ethylenedioxythiophene (EDOT) electropolymerization in aqueous medium in order to investigate its effects on conducting polymer properties. It was shown that mass transfer increases under ultrasound irradiation which improved electropolymerization and the comparison with experiments carried out at the same mass transfer level (4.6 × 10(-5) ms(-1)) puts in evidence that stirring effect is not the only phenomenon induced by ultrasound during electrodeposition. PEDOT films elaborated under ultrasonication present increased doping levels revealed by X-ray Photoelectron Spectroscopy (XPS) analysis, especially in the case of thick films (measured by mechanical probe), thanks to better incorporation of counter ions within polymer matrix as another consequence of mass transport improvement under ultrasound and probably film heating by wave absorption for the highest thicknesses. A dilation of the film under sonication leading to an increase in film thickness was also highlighted. Finally, a refining of the surface structure was also observed via SEM imaging.

Electrosynthesis and characterization of conducting polypyrrole elaborated under high frequency ultrasound irradiation

The effects of high frequency ultrasound (500kHz) on pyrrole electropolymerization in sodium perchlorate aqueous medium have been investigated. Cyclic voltametry studies showed that there is no influence on pyrrole oxidation potential. Scanning Electron Microscopy (SEM) imaging, and mechanical and optical profiling, revealed thinner, denser and more homogeneous surface structure for polypyrrole films elaborated under ultrasound irradiation. This is attributed to cavitation bubble asymmetric collapse close to the interface, which should induce changes in the nucleation-growth mechanism during the first polymerization stage. An increase of approximately 27% in doping level for sonicated films was revealed by X-ray Photoelectron Spectroscopy (XPS) analyses.

Corrosion protection by sonoelectrodeposited organic films on zinc coated steel.

A variety of coatings based on electrosynthesized polypyrrole were deposited on zinc coated steel in presence or absence of ultrasound, and studied in terms of corrosion protection. Cr III and Cr VI commercial passivation were used as references. Depth profiling showed a homogeneous deposit for Cr III, while SEM imaging revealed good surface homogeneity for Cr VI layers. These chromium-based passivations ensured good protection against corrosion. Polypyrrole (PPy) was also electrochemically deposited on zinc coated steel with and without high frequency ultrasound irradiation in aqueous sodium tartrate-molybdate solution. Such PPy coatings act as a physical barrier against corrosive species. PPy electrosynthesized in silent conditions exhibits similar properties to Cr VI passivation with respect to corrosion protection. Ultrasound leads to more compact and more homogeneous surface structures for PPy, as well as to more homogeneous distribution of doping molybdate anions within the film. Far better corrosion protection is exhibited for such sonicated films.

Influence of modification time and high frequency ultrasound irradiation on self-assembling of alkylphosphonic acids on stainless steel: Electrochemical and spectroscopic studies.

Self-assembly of alkylphosphonic acids on stainless steel was investigated under different conditions. Four different alkylphosphonic acids exhibiting alkyl chain of various size were synthesized and studied: butylphosphonic acid (C4P), octylphosphonic acid (C8P), decylphosphonic acid (C10P), and hexadecylphosphonic acid (C16P). Electrochemistry experiments were extensively carried out in order to determine electrochemical surface blocking of adsorbed layers in function of grafting time. In term of surface blocking, an 8h modification time was optimal for all alkylphosphonic acids. Longer immersion times lead to degradation of adsorbed layers. For the first time, grafting of C16P was studied under high frequency ultrasound irradiation. Interestingly, grafting process is highly accelerated under sonication and well-covering C16P modified substrates are obtained after 1h of immersion under ultrasound irradiation. This would allow to elaborate high-quality alkylphosphonic acids modified samples within much shorter times. Water contact angles measurements and X-ray Photoelectrons Spectroscopy (XPS) confirmed presence of adsorbed alkylphosphonic acids on stainless steel surface. A very tight link between electrochemical blocking, surface hydrophobicity and species chemical grafting was established.