Julienne Charlier

Localized Electrografting of Vinylic Monomers on a Conducting Substrate by Means of an Integrated Electrochemical AFM Probe

Combinations of scanning electrochemical microscopy (SECM) with other scanning probe microscopy techniques, such as atomic force microscopy (AFM), show great promise for directing localized modification, which is of great interest for chemical, biochemical and technical applications. Herein, an atomic force scanning electrochemical microscope is used as a new electrochemical lithographic tool (L-AFM-SECM) to locally electrograft, with submicrometer resolution, a non-conducting organic coating on a conducting substrate.

Electropolymerization of methacrylonitrile and N-vinyl-2-pyrrolidone as probed by an EQCM

The electropolymerization of methacrylonitrile (MAN) and N-vinyl-2-pyrrolidone (NVP) in anhydrous acetonitrile has been followed in situ using an electrochemical quartz crystal microbalance (EQCM). These two monomers essentially differ in that MAN leads to both a grafted polymer and a polymer formed in solution, while NVP only delivers the grafted polymer. For both molecules, our results indicate that the frequency response of the EQCM anticipates the voltammetric response. In the case of MAN, the admittance of the EQCM shows a considerable increase which is synchronized with the voltammetric peak. Alternatively, in the case of NVP, the admittance of the EQCM remains almost constant during the course of the experiment. These results lead us to the proposal that: (i) the eigenfrequency variations of the EQCM may be related to mass changes on the surface of the quartz crystal in the case of the electropolymerization of NVP molecules over the whole potential range, while the same is true only over a few hundreds of mV before the peak in the case of MAN; (ii) poly-NVP films grow directly from the surface of the electrode, while at least two regimes are detectable in the case of MAN.

Local silicon doping as a promoter of patterned electrografting of diazonium for directed surface functionalization

We study the influence of locally doped silicon substrates on the electroreduction of diazonium salts. Our results show that the reduction of diazonium salts occurs at moderate potentials compared to the flat band potential of the semiconducting electrode. The underlying doping directs the electrografting, preferentially over doped areas of the substrate. High resolution spatially resolved X-ray photoelectron spectroscopy analysis using a new X-ray photoelectron emission microscope (XPEEM) and soft X-ray synchrotron radiation yields the thickness of the native oxide of the micron scale doped pattern on the substrate. The results as a function of both parameters—reduction potential compared to the flat band potential and thickness of the oxide layer—are discussed. These new results are then compared to data obtained on the localized electrografting of vinylic monomers.

The in-situ characterization and structuring of electrografted polyphenylene films on silicon surfaces. An AFM and XPS study.

An atomic force microscope was used so as to structure by nanofriction films of polynitrophenylene electrografted on substrates of n-type silicon (100) with the native oxide on the top of the surface. AFM measurements of thin films thickness have been carried out in the electrolytic solution for different applied potentials during the electrografting. This investigation allows (i) to determine the relationship between the applied potential and the final thickness of electrografted polyphenylene films and (ii) to specify how the thin layers grow. XPS analysis confirmed the AFM observations on (i) the effective shaving of the grafted polymer chains under mechanical stress and (ii) the existence of a potential threshold for electrografting a polyphenylene film on silicon oxide surfaces. The presence of a residual film in the rubbed zone was attributed to stronger interactions between the first electrografted layer and the native oxide of silicon (through Si-C or/and Si-O-C bonds) than those insuring the cohesion of the multilayer (C-C and C-N bonds).

Étude de la complexation des lanthanides trivalents par les six isomères de l'acide diaminocyclohexane-tétraacétique : Partie 3. Relation entre les Constantes d'Acidité et la Structure Moleculaire des Chélatants

(Study of the complexation of trivalent lanthanides by the six isomers of diaminocyclohexanetetraacetic acid. Part 3. Relationship between the acidity constants and the molecular structure of the ligands.) Potentiometric measurements of the acidity constants of the six isomers of diaminocyclohexane-N,N,N′,N′-tetraacetic acid (DCTA) are reported for an ionic strength of 1 mol l−1 (KCl) at 25°C. The values of the two constants Ka3 and Ka4 are correlated with the maximum N—N distance for each ligand. Ethylenediamine-N,N,N′,N′-tetraacetic acid (EDTA) and some homologous ligands, including specially synthesized, 1,8-diaminooctane-N,N,N′,N′-tetraacetic acid and 1,10-diaminodecane-N,N,N′,N′-tetraacetic acid, are studied under the same conditions. It is proved that there is a relationship between the molecular structure and the affinity for protons.

Ring hydrolysis in the electro-oxidation of pyrrolidone analogues

Upon oxidation in acetonitrile, pyrrolidone analogues, namely pyrrolidone, methyl-pyrrolidone, ethyl-pyrrolidone and N-vinyl pyrrolidone, afford thin organic films which can be analyzed by X-ray photoelectron spectroscopy. One common singular feature is noted in the XPS spectra: the advent of a very high energy C1s peak (288.9 eV), indicating the formation of a molecular structure with a carbon atom in an unusually electronegative environment. Considering the recently proposed reaction mechanisms for the oxidation of pyrrolidone analogues, a theoretical study is carried out: several molecular structures are proposed, on which very accurate calculations of core-electron binding energies are performed using the density functional theory. On comparison with the complete experimental spectrum, it is proposed that this peculiar high-energy peak stems from the opening of the pyrrolidone ring to yield carboxylic acid groups.

Influence of the Electronic Structure of the Metal at the Polymer/Metal Interface: A Tentative Interpretation on the Basis of Lewis Acid-Base Reactions

Abstract In the present paper, we examine the link between theoretical qualitative predictions made on the grounds of the Lewis acid-base concept and the actual interface built between polyamide-6,6 (PA-6,6) and copper, and PA-6,6 and platinum. By using a combination of very-surface-sensitive photoemission spectroscopies and model polymers, it becomes possible to obtain important information about the chemical nature of the polymer/metal interface. Our experiments show a complete dissociative chemisorption of the polymer on Pt, while PA-6,6 retains its chemical integrity on copper.

Grafting and growth of poly(N‐vinyl‐2‐pyrrolidone) films on platinum and gold electrodes

Application of an anodic potential under recycled argon atmosphere to a highly concentrated solution of N‐vinyl‐2‐pyrrolidone (5 mol.dm−3) allows to graft and polymerise the monomer onto a Pt or Au electrode. XPS, UPS and IRRAS spectroscopies reveal the presence of thin PVP films on these surfaces. XPS data point to the formation of C‐metal bonds and support the grafting hypothesis of polymer chains onto the surface of the electrode. XPS and UPS studies performed after annealing indicate that the different structures of the polymer are stable up to 200 °C under ultra high vacuum and confirm the chemisorbed nature of the surface bond. A cationic mechanism is proposed for the grafting and the polymerisation. Preliminary attempts to relax the preparation conditions show that films can be obtained in ambient atmospheric conditions, but their thickness is reduced compared to those obtained under recycled argon conditions.

Étude de la complexation des lanthanides trivalents par l'isomère trans-1,3 de l'acide cyclopentanediaminotétraacétique

(Study of the complexation of the lanthanides by the trans-1,3 isomer of cyclopentanediaminotetraacetic acid.) The various steps of the synthesis of trans-1,3-cyclopentanediaminotetraacetic acid are briefly discussed and the acidity constants of this chelating agent are reported, together with the stability constants of its 1:1 complexes with the trivalent lanthanides; the results are obtained at 25° C for an ionic strength of 1 mol l−1 (KCl) by coulometric titrations with potentiometric detection. The values reported are compared with the corresponding data obtained with other polyaminopolyacetic acids.