Catherine Combellas

Sterically hindered diazonium salts for the grafting of a monolayer on metals.

An organic monolayer is obtained on Cu, Au, and SiH by electrografting 3,5-bis-tert-butyl benzenediazonium tetrafluoroborate, as evidenced by cyclic voltammetry, IR-ATR, and ellipsometry. This results from the bulky groups at the 3,5-positions that sterically hinder the growth of the layer.

Steric Effects in the Reaction of Aryl Radicals on Surfaces

Steric effects are investigated in the reaction of aryl radicals with surfaces. The electrochemical reduction of 2-, 3-, 4-methyl, 2-methoxy, 2-ethyl, 2,6-, 2,4-, and 3,5-dimethyl, 4-tert-butyl, 3,5-bis-tert-butyl benzenediazonium, 3,5-bis(trifluoromethyl), and pentafluoro benzenediazonium tetrafluoroborates is examined in acetonitrile solutions. It leads to the formation of grafted layers only if the steric hindrance at the 2- or 2,6-position(s) is small. When the 3,5-positions are crowded with tert-butyl groups, the growth of the organic layer is limited by steric effects and a monolayer is formed. The efficiency of the grafting process is assessed by cyclic voltammetry, X-ray photoelectron spectroscopy, infrared, and ellipsometry. These experiments, together with density functional computations of bonding energies of substituted phenyl groups on a copper surface, are discussed in terms of the reactivity of aryl radicals in the electrografting reaction and in the growth of the polyaryl layer.

Correlated Electrochemical and Optical Detection Reveals the Chemical Reactivity of Individual Silver Nanoparticles

Electrochemical (EC) impacts of single nanoparticles (NPs) on an ultramicroelectrode are coupled with optics to identify chemical processes at the level of individual NPs. While the EC signals characterize the charge transfer process, the optical monitoring gives a complementary picture of the transport and chemical transformation of the NPs. This is illustrated in the case of electrodissolution of Ag NPs. In the simplest case, the optically monitored dissolution of individual NPs is synchronized with individual EC spikes. Optics then validates in situ the concept of EC nanoimpacts for sizing and counting of NPs. Chemical complexity is introduced by using a precipitating agent, SCN(-), which tunes the overall electrodissolution kinetics. Particularly, the charge transfer and dissolution steps occur sequentially as the synchronicity between the EC and optical signals is lost. This demonstrates the level of complexity that can be revealed from such electrochemistry/optics coupling.

Surface modification of halogenated polymers. 4. Functionalisation of poly(tetrafluoroethylene) surfaces by diazonium salts

Reduced PTFE can be grafted by nitro and bromo-phenyl diazonium tetrafluoroborate salts in a manner similar to that used for carbon, except that no application of a reductive potential during grafting was required. Grafting was evidenced by cyclic voltammetry, X-ray fluorescence or ToF-SIMS. Nitro- and bromo-phenyl moieties were covalently linked to the PTFE material and could be eliminated only by abrasion.

Scanning Electron Microscopy Investigation of Molecular Transport and Reactivity within Polymer Brushes

Scanning electrochemical microscopy (SECM) allows investigation of the transport of redox probes within polymer brushes grown by atom-transfer radical polymerization (ATRP) from gold electrodes. By combination with cyclic voltammetry, the permeation of aqueous or organic redox probes is described and quantified in poly(glycidyl methacrylate) (PGMA) and polystyrene (PS). It is related to the chemical nature of both the probe and its environment (the solvent and the polymer phases). This study anticipates the permeation of reactive species within polymer brushes for further etching. The SECM reductive etching of the terminal C-Br bond of PGMA or PS macroinitiator layers is then investigated for different polymer thicknesses. The incomplete reductive etching of the macroinitiator layers is in agreement with the low permeability of the etchant within such polymer brushes and with the distribution of the terminal C-Br bonds throughout the brush. SECM proves to be a convenient tool for patterning such macroinitiator surfaces to form channels in block-copolymer structures. The combination of both analytical and patterning investigations enables one to anticipate and understand the reactivity of grafted macromolecules.

Electrografting of Diazonium-Functionalized Polyoxometalates: Synthesis, Immobilisation and Electron-Transfer Characterisation from Glassy Carbon

Polyoxometalates (POMs) are attractive candidates for the rational design of multi-level charge-storage materials because they display reversible multi-step reduction processes in a narrow range of potentials. The functionalization of POMs allows for their integration in hybrid complementary metal oxide semiconductor (CMOS)/molecular devices, provided that fine control of their immobilisation on various substrates can be achieved. Owing to the wide applicability of the diazonium route to surface modification, a functionalized Keggin-type POM [PW11 O39 {Ge(p-C6 H4 -CC-C6 H4 -

Surface modification of halogenated polymers: 5. Localized electroless deposition of metals on poly(tetrafluoroethylene) surfaces

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Deciphering the Elementary Steps of Transport-Reaction Processes at Individual Ag Nanoparticles by 3D Superlocalization Microscopy

)}](3-) bearing a pending diazonium group was prepared and subsequently covalently anchored onto a glassy carbon electrode. Electron transfer with the immobilised POM was thoroughly investigated and compared to that of the free POM in solution.

Electrochemical and spectroscopic investigation of counterions exchange in polyelectrolyte brushes.

Localized metallization of polytetrafluoroethylene (PTFE) can be achieved by an electroless deposition procedure, once PTFE has been reduced locally at the contact or in the vicinity of an electrode by scanning electrochemical microscope (SECM). This process takes advantage of the n-doped character of polymeric carbon obtained when reducing PTFE. Metallization was evidenced with Au, Ag and Cu by cyclic voltammetry, SECM, MEB and X-ray fluorescence.

Solvent effect on the intramolecular charge transfer of zwitterions. Structures and quadratic hyperpolarizabilities

Transport-reaction processes at individual Ag nanoparticles (NPs) are studied using electrochemistry coupled with in situ 3D light scattering microscopy. Electrochemistry is used to trigger a (i) diffusiophoretic transport mode capable of accelerating and preconcentrating NPs toward an electrode and (ii) subsequent diffusion-controlled oxidation of NPs. Individual NP dissolution rate, analyzed using optical modeling, suggests the intervention of insoluble products. New insights into diverse NPs behaviors highlight the strength of coupled optical-electrochemical 3D microscopies for single-NP studies.