Showing papers by "Michel Delamar published in 2000"

Chemical deposition and characterization of thin polypyrrole films on glass plates: role of organosilane treatment

Abstract: Thin chloride-doped polypyrrole films (PPyCl) were deposited chemically onto untreated and silane-treated planar glass plates from aqueous solutions. The organosilanes used to treat the glass substrates were methyltriethoxysilane (Cl), propyltrimethoxysilane (C3), octyltrimethoxysilane (C8) and aminopropyltriethoxysilane (APS). The decreasing order of hydrophobic character of silane-treated glass slides, as measured by water contact angle measurements, was glass–APS ≅ glass–C8 > glass–C3 > glass–C1 > glass. X-ray photoelectron spectroscopy was used to determine the surface chemical composition of the glass plates before and following coating with the silane coupling agents and/or the PPy thin layer, respectively. The attenuation in intensity of the glass Na1 s peak enabled the average thickness of the various organosilane overlayers to be estimated. Atomic force microscopy showed that the morphology of the organosilane overlayers was islandlike. The domains have a structure which depends upon the nature of the organosilane in question. Scanning electron microscope images showed that the morphology of the PPyCl thin films was homogeneous when coated onto glass–APS and glass–C8, but wrinkled at the surface of glass, glass–C1 and glass–C3 plates. Qualitative peel tests using 3M adhesive tape showed very good adhesion of PPyCl to the glass–APS substrate, whereas adhesion was fairly poor in the case of glass–PPy and PPy–alkylsilane–glass interfaces. The results of this multitechnique study suggest that hydrophobic interactions are important to obtain homogeneous and continuous thin PPy films, but Lewis acid–base interactions are the driving forces for strong and durable PPy–glass adhesion.

Study of DNA adsorption on polypyrrole: interest of dielectric monitoring

Abstract: The interest of high frequency impedance measurements performed on decanted solids was demonstrated for the in situ investigation of DNA adsorption onto polypyrrole (PPy). The dielectric method was first applied to distinguish between polymers containing different dopant and to monitor their ion-exchange occurring when PPy was contacting a phosphate buffer solution. Results were compared to those obtained by X-ray photoelectron spectroscopy (XPS) and ion-exchange chromatography. Afterwards, the effects of DNA adsorption were investigated in 0.01 M phosphate buffer at pH 7. A significant decrease in the dielectric parameters was observed upon the adsorption, as a result of the coverage of the conductive PPy by an insulating layer of DNA, while maintaining, however, the mobility of doping anions in the bulk of the polymer. Irreversibility of the adsorption process was assessed. Some conformational changes of the adsorbed DNA have been suspected to occur during the deposition of increasing amounts of DNA.