Mireille Turmine

A ZnO nanowire array film with stable highly water-repellent properties

Highly water-repellent surfaces have been prepared from arrayed nanowires of zinc oxide (ZnO) by a treatment with stearic acid. The layers are electrochemically deposited on a nanocrystalline seed layer from an oxygenated aqueous zinc chloride solution. An advancing contact angle (CA) as high as 176° is obtained with a very small hysteresis ~1°. These results, supplemented by infrared spectroscopy, show that the stearic acid forms a very well-packed self-assembled monolayer. The CA measurements show a very good stability of the treated surface even when exposed to harsh conditions or long-term ambient illumination.

Highly hydrophilic surfaces from polyglycidol grafts with dual antifouling and specific protein recognition properties.

Homopolymer grafts from α-tert-butoxy-ω-vinylbenzyl-polyglycidol (PGL) were prepared on gold and stainless steel (SS) substrates modified by 4-benzoyl-phenyl (BP) moieties derived from the electroreduction of the parent salt 4-benzoyl benzene diazonium tetrafluoroborate. The grafted BP aryl groups efficiently served to surface-initiate photopolymerization (SIPP) of PGL. In similar conditions, SIPP of hydroxyethyl methacrylate (HEMA) permitted the production of PHEMA grafts as model surfaces. Water contact angles were found to be 66°, 15°, and 0° for SS-BP, SS-PHEMA, and SS-PPGL, respectively. The spontaneous spreading of water drops on SS-PPGL was invariably observed with 1.5 μL water drops. PPGL thus appears as a superhydrophilic polymer. Resistance to nonspecific adsorption of proteins of PPGL and PHEMA grafts on gold was evaluated by surface plasmon resonance (SPR) using antibovine serum albumin (anti-BSA). The results conclusively show that PPGL-grafts exhibit enhanced resistance to anti-BSA adsorption compared to the well-known hydrophilic PHEMA. PPGL grafts were further modified with BSA through the carbonyldiimidazole activation of the OH groups providing immunosensing surfaces. The so-prepared PPGL-grafted BSA hybrids specifically interacted with anti-BSA in PBS as compared to antimyoglobin. It is clear that the superhydrophilic character of PPGL grafts opens new avenues for biomedical applications where surfaces with dual functionality, namely, specific protein grafting together with resistance to biofouling, are required.

Electrografted aryl diazonium initiators for surface-confined photopolymerization: a new approach to designing functional polymer coatings.

This article reports on the preparation of polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(2-hydroxyethyl methacrylate) (PHEMA) ultrathin grafts on gold substrates modified by 4-benzoylphenyl (BP) moieties derived from the electroreduction of the parent diazonium salt BF(4)(-), (+)N(2)-C(6)H(4)-CO-C(6)H(5) (DS). The grafted organic species -C(6)H(4)-CO-C(6)H(5) was found to be very effective in the surface-initiating photopolymerization (SIPP) of vinylic monomers in the presence of an aromatic tertiary amine co-initiator acting as a hydrogen donor. This novel tandem diazonium salt electroreduction/SIPP was found to be effective in grafting PS, PMMA, and PHEMA from the surface of gold-coated silicon wafers. The polymer films were characterized in terms of chemical structure and wettability by infrared reflection absorption spectroscopy and X-ray photoelectron spectroscopy, and contact angle measurements, respectively. The polymer grafts were further evaluated as adsorbents for bovine serum albumin (BSA) used as a model protein. It was found gold/PHEMA resisted BSA adsorption because of its hydrophilic character, whereas PS and PMMA grafts adsorbed BSA via interfacial hydrophobic interaction. The XPS-determined extent of adsorbed BSA was found to increase linearly with the hydrophobic character of the polymer grafts as measured by water contact angles. This work shows that this novel tandem diazonium salt electroreduction/SIPP is a facile, ultrafast, efficient protocol for grafting polymer chains to surfaces. It broadens the enormous possibilities offered by aryl diazonium salts to generate functional organic coatings.

Structure of Aqueous Solutions of Ionic Liquid 1-Butyl-3-methylimidazolium Tetrafluoroborate by Small-Angle Neutron Scattering

The structure of aqueous solutions of a prototype ionic liquid, the short alkyl chain 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]) has been investigated by small-angle neutron scattering. Concentration fluctuations and Kirkwood-Buff integrals have been calculated, and the results are in good agreement with corresponding data calculated herein from vapor pressure measurements. The large concentration fluctuations and Kirkwood-Buff integral values indicate that the system is in the vicinity of phase separation, which is known to occur some 20 K below room temperature, at a salt mole fraction of around 0.075.

Ruthenium nanoparticles in ionic liquids: structural and stability effects of polar solutes

Ionic liquids are a stabilizing medium for the in situ synthesis of ruthenium nanoparticles. Herein we show that the addition of molecular polar solutes to the ionic liquid, even in low concentrations, eliminates the role of the ionic liquid 3D structure in controlling the size of ruthenium nanoparticles, and can induce their aggregation. We have performed the synthesis of ruthenium nanoparticles by decomposition of [Ru(COD)(COT)] in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C(1)C(4)Im][NTf(2)], under H(2) in the presence of varying amounts of water or 1-octylamine. For water added during the synthesis of metallic nanoparticles, a decrease of the solubility in the ionic liquid was observed, showed by nanoparticles located at the interface between aqueous and ionic phases. When 1-octylamine is present during the synthesis, stable nanoparticles of a constant size are obtained. When 1-octylamine is added after the synthesis, aggregation of the ruthenium nanoparticles is observed. In order to explain these phenomena, we have explored the molecular interactions between the different species using (13)C-NMR and DOSY (Diffusional Order Spectroscopy) experiments, mixing calorimetry, surface tension measurements and molecular simulations. We conclude that the behaviour of the ruthenium nanoparticles in [C(1)C(4)Im][NTf(2)] in the presence of 1-octylamine depends on the interaction between the ligand and the nanoparticles in terms of the energetics but also of the structural arrangement of the amine at the nanoparticles surface.

Surfactant self-assembly nanostructures in protic ionic liquids.

The existence and properties of mesoscopic self-assembly structures formed by surfactants in protic ionic liquid solutions are reported. Micellar aggregates of n-alkyltrimethylammonium (n = 10, 12, 14, 16) chlorides and bromides and of n-alkylpyridinium (n = 12, 16) chlorides in ethylammonium nitrate and propylammonium nitrate were observed by means of several experimental techniques, including surface tension, transmission electron micrography, dynamic light scattering, and potentiometry using surfactant-selective electrodes. The effect of the alkyl chain length of both solute and solvent molecules on the critical micelle concentration is discussed, and a Stauff-Klevens law is seen to apply to surfactant solutions in both protic ionic liquids. The counterion role is also a matter of study in the case of alkyltrimethylammonium-based surfactants, and the presently reported evidence suggests that the place of the surfactant counterion in the Hoffmeisters series could determine its effect on micellization in IL solution. The size distribution of the aggregates is also analyzed together with the Gibbs free energies of micellization and the minimum surface area per monomer in all of the studied cases. All of the hereby reported evidence suggests that the negative entropic contribution arising from the release of the solvent layer upon micellization is also the driving force of conventional surfactant self-association in protic ionic liquids.

Stepwise Aggregation of Dimethyl-di-n-octylammonium Chloride in Aqueous Solutions: From Dimers to Vesicles

The self-aggregation of dimethyl-di-n-octylammonium chloride, in diluted aqueous solutions, was studied with various experimental and theoretical techniques: zetametry, conductimetry, dimethyl-di-n-octylammonium and chloride-selective electrodes, tensiometry, NMR spectroscopy ((1)H and DOSY), and molecular modeling (PM3 and molecular dynamic). The combination of the data obtained by these techniques led us to propose a stepwise aggregation process with increasing concentration: dimers (0.2-10 mM), bilayers (10-30 mM), and finally vesicles (>30 mM).

Aryl Diazonium Salts for Carbon Fiber Surface-Initiated Atom Transfer Radical Polymerization

, +N2-C6H4-CH(CH3)-Br diazonium salt was electrochemically reduced in order to graft phenylethyl bromide groups to carbon fibers. The pretreated fibers (CF-Br) served as macroinitiators of atom transfer radical polymerization (ATRP) of vinylic monomers. This procedure combining a diazonium salt and ATRP permitted the polymerization of butyl, glycidyl and hydroxyethyl methacrylates at the surface of carbon fibers (CF) resulting in CF-PBMA, CF-PGMA, and CF-PHEMA hybrids, respectively. The surface chemistry and wettability of these hybrids were interrogated by XPS and water contact angles. The change in the wettability of carbon fibers reflects the chemical nature of the tethered polymer chains as the wettability decreases in the order CF-PHEMA > CF-PGMA > CF-PBMA > CF. Furthermore, CF-PHEMA was found to resist non-specific adsorption bovine serum albumin (BSA) compared with the more hydrophobic CF-PBMA system. This work shows that the use of diazonium salt is a facile, new surface chemistry option for grafting initiator of ATRP to carbon fiber. This strategy ensures a good carbon fiber-polymer adhesion through covalent bonds.

Solubility of nanoparticles: nonextensive thermodynamics approach

We show in this study that the concepts of nonextensive thermodynamics, introduced in a previous work, can be used to express the variations of the solubility of nanoparticles and porous materials according to their mass by power laws, without the need to resort to fractal dimensions. This results in the demonstration of the Ostwald–Freundlich relation. Our approach is based on a thermodynamic description involving the introduction in the internal energy expression of an extensity, χ. χ is an Eulers function of the particle mass with a homogeneity degree, m, which can be other than one; m is the thermodynamic dimension of the system. We use this approach to simulate various behaviours, and show that an increase in solubility can be either higher or lower than that envisaged by the Ostwald–Freundlich relation.

Pseudolattice theory of the surface tension of ionic liquid-water mixtures.

A theoretical model for ionic liquids (ILs) based on a pseudoreticular structural model for the bulk mixture is reported. The original Bahe-Varela pseudolattice theory of concentrated ionic solutions is modified and the short-range interactions modeled by a Lennard-Jones potential. In this framework, the surface tension of the pure IL is calculated and the correct dependence of this magnitude on the density of the liquid, as provided by the parachor, is recovered. The anions in the mixture are assumed to form a continuum structureless neutralizing background, and that the organic cations and water molecules are placed in the nodes of the pseudolattice. The surface pressure of IL-water mixtures is calculated using a localized model for the adsorption of particles in the surface of the mixture and a mean-field Bragg-Williams approximation for the chemical potential of the adsorbed particles in the pseudolattice. The theoretical predictions are tested with experimental data of several ionic liquid aqueous mixtures.