Roger Legras

Giant Magnetoresistance in Magnetic Multilayered Nanowires

Giant magnetoresistance (GMR) is observed in a new type of nanostructured material consisting of magnetic multilayered nanowires formed by electrodeposition into nanometer-sized pores of a template polymer membrane. The composition of these nanowires is modulated over nanometer length scales with distinct magnetic and nonmagnetic metallic layers. Magnetoresistance measurements with the current perpendicular to the layers were performed on the array of parallel nanowires. GMR of about 15% was observed at room temperature on Co/Cu multilayered nanowires

Chemical synthesis of polypyrrole: structure–properties relationship

Nanostructures composed of polypyrrole (PPy) are obtained by chemically synthesizing PPy within the pores of microporous and nanoporous Particle Track-etched Membranes (PTM). Hollow tubules are formed because polypyrrole initially deposits on the surface of the pores walls. By running successive syntheses, we: have obtained wires (filled tubules). These nanoscopic materials show enhancements in electronic conductivity compared to analogous polymer bulk conductivity. This work highlights the difficulty in obtaining an absolute value of the electronic conductivity. Pores shape and pores filling must be well tailored because these parameters are absolutely required to determine the conductivity. So, the morphologies and the structures of the nanomaterials have been carefully analyzed by Field-Effect Scanning Electron Microscopy (FE-SEM). The Raman spectroscopy was used to correlate the molecular structure of the nanoscopic tubules with their conducting properties by determining the relative conjugation length in the PPy chains. Raman data show that the ordering of the polymer chains is improved when the pores diameter decreases and is responsible for the enhancement in conductivity

Chemical and electrochemical synthesis of polyaniline micro- and nano-tubules

Micro- and nano-structures composed of polyaniline (PANi) have been prepared by chemical and electrochemical oxidative polymerization of aniline within the pores of particle track-etched membranes (PTM). Their morphology has been studied by field-emission scanning electron microscopy. Hollow tubules are formed because PANi initially deposits on the surface of the pore walls. Raman spectroscopy was used to probe the oxidative state of PANi in order to optimize the chemical polymerization conditions with respect to the electrical conductivity. The nanoscopic materials show an enhancement of the electronic conductivity compared to analogous polymer bulk conductivity

On the Molecular-weight Determination of a Poly(aryl-ether-ether-ketone) (peek)

Abstract Attempts have been made to determine the weight average molecular weight ( M W ), the radius of gyration ( R G ) and the second virial coefficient (A2) of five samples of poly(ether-ether-ketone) (PEEK) by light scattering (LS) in concentrated sulphuric acid. Account has been taken of the sulphonation of the polymer. Correlations between LS-molecular weights, melt viscosities and intrinsic viscosities in sulphuric acid or in a 50 50 phenol-trichlorobenzene mixture have been established. Gel permeation chromatography (g.p.c.) analyses at 115°C have been performed in this latter solvent and two calibration methods were compared.

Quantification of the maleic anhydride grafted onto polypropylene by chemical and viscosimetric titrations, and FTIR spectroscopy

An acid-base titration method for an accurate and reproducible quantification of maleic anhydride grafted onto polyolefins is proposed. The use of an organic base (tetra-butylammonium hydroxide) enhances the base solubility in organic solvents and prevents phenomena like coarcervation. The titration goes on until the visual endpoint of a coloured indicator, corresponding to the neutralisation of the grafted functions. Bromothymol blue is chosen as the coloured indicator to determine this equivalence point. It is critically correlated with a Fourier transform-infrared spectroscopy quantification developed previously by De Roovers et al. [J Polym Sci, Part A: Polym Chem 1995;33:829] and with a viscosimetric titration method here-proposed Finally, the titration mechanism is confirmed by the titration of some well-defined amount of anhydride model compounds and by FTIR analyses of their products after titration

The anhydride content of some commercial PP-g-MA: FTIR and titration

A set of anhydride-grafted polypropylenes was collected from various companies. They were studied in light of our recent results on polypropylene melt grafted with maleic anhydride.(1) This work confirmed that an important decrease of the anhydride content is recorded on heating or washing, due to the elimination of free, ungrafted products, respectively, by sublimation of maleic anhydride and by polymaleic anhydride solubilization. The deconvolution of the infrared spectra of washed anhydride-grafted polypropylenes (PP-g-MA) revealed two types of grafted anhydride: succinic anhydride form and polymaleic anhydride form. All in all, four forms of anhydride functions were detected: two grafted and two free, each being either on monomeric or polymeric forms. Nevertheless, one PP-g-MA (Hercoprime) can be distinguished by its very high grafting level. This polymer is therefore discussed in more detail. Finally, all the present results are discussed with regard to the principal applications of the PP-g-MA as a blend compatiblizer or as an adhesion promoter

Thermal stability and crystallization of poly (aryl ether ether ketone)

The molecular weight distribution of poly(aryl ether ether ketone) (PEEK) has been measured as a function of the melt holding temperature and time in air and in an inert environment. A branching mechanism was observed to occur in the usual melt processing conditions, which was much stronger in air than in vacuum or nitrogen. This degradation mechanism is correlated to a volatile emission observed with thermogravimetric analysis. The influence of the degradation on the PEEK crystallization is discussed. A considerable decrease in crystallization rate is observed associated with the decreased molecular mobility due to the molecular weight increase. and a crystallinity decrease associated with the structural defects introduced along the chains by the branching process. The self-nucleation in PEEK has also been examined through optical microscopy. It was concluded that to get rid of the self-nucleation phenomenon, it is necessary to bring the polymer to temperatures where degradation is already present.

Track-etch templates designed for micro- and nanofabrication

This paper reports on the advances made in the laboratory in the development of porous media by track-etching process, and on their use by research partners as templates for the micro- or nanofabrication of polymeric and metallic wires or tubules with interesting properties. It mainly relates to the development of nanoporous polycarbonate-based templates, and more precisely to pore-shape control in polycarbonate films, to the development of supported track-etch templates and to the feasibility of template patterning; recent results on the development of templates from polyimide support are also reported. Finally, some nanontaterial synthesis processes and properties are listed, with references to published papers

Electrochemically synthesized polypyrrole nanotubules: Effects of different experimental conditions

Nanotubules of polypyrrole (PPy) were electrochemically synthesized using the pores of nanoporous polycarbonate (PC) particle track-etched membranes (PTM) as templates. The influence of some conditions of electrosynthesis (electrochemical method, monomer concentration, electrolyte concentration and nature) on the kinetics of pyrrole electropolymerization and on the morphology of the obtained nanomaterials has been investigated. In particular, the empirical kinetics of the electrochemical generation of polypyrrole-perchlorate (PPy-ClO4) from aqueous solution, at 0.8 V (vs SCE) was followed by electrical charges measurement. The orders with respect to pyrrole and LiClO4 are 0.34 and 0.70 respectively. The electrogeneration of polypyrrole-polystyrenesulfonate (PPy-PSS) was also followed and shows that an increase of the electrolyte concentration increases the polymerization rate at constant potential. Finally, the morphology of PPy nanotubules doped with LiClO4 and NaPSS has been studied by high resolution emission SEM and by TEM

Sizing Removal and Functionalization of the Carbon-fiber Surface Studied By Combined Tof Sims and Xps

Time-of-flight secondary ion mass spectrometry (TOF SIMS) and X-ray photoelectron spectroscopy (XPS) have been jointly used to study a two-step surface processing of AS4 carbon fiber: extraction of sizing in CH2Cl2 and functionalization with trimellitic anhydride. The combined information on molecular specificity obtained with TOF SIMS and quantification obtained with XPS allows us to follow qualitatively and quantitatively the changes in functional groups on the carbon surface. The results show that the sizing on AS4 contains at least four different compounds. These compounds can be extracted in CH2Cl2 and the elimination is almost complete for silicone. The functionalization of AS4 with trimellitic anhydride has been realized. The reaction takes place between the amine groups on the carbon fiber and the two types of functional groups in trimellitic anhydride.