Time filter

Source Type

Fameau A.-L.,French National Institute for Agricultural Research | Zemb T.,CNRS Marcoule Institute for Separative Chemistry
Advances in Colloid and Interface Science

Fatty acids can self-assemble under various shapes in the presence of amines or cationic components. We assemble and compare these types of self-assembly leading toward a catanionic system either with a cationic surfactant or with an amine component playing the role of counter-ion. First, we focus on the molar ratio as a key driving parameter. Known and yet un-known values from other quantities governing the colloidal properties of these systems such as structural surface charge, osmotic pressure, molecular segregation, rigidity, in plane colloidal interactions and melting transition are discussed. We include also recent results obtained on the interfacial and foaming properties of these systems. We will highlight the specificity of these self-assemblies leading to unusual macroscopic properties rich of robust applications. © 2013 Elsevier B.V. Source

Martinelli A.,Chalmers University of Technology | Marechal M.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | Ostlund A.,Chalmers University of Technology | Cambedouzou J.,CNRS Marcoule Institute for Separative Chemistry
Physical Chemistry Chemical Physics

We report on how the local structure and the diffusional motion change upon increasing the alkyl chain length in 1-alkyl-3-methylimidazolium cation ionic liquids. This study has been performed by combining pulse field gradient (PFG) nuclear magnetic resonance (NMR) spectroscopy and small angle X-ray scattering (SAXS) experiments. The cationic side chain length varies from ethyl (n = 2) to hexadodecyl (n = 16), while the anion is always bis(trifluoromethanesulfonyl) imide (TFSI). We find that the self-diffusivity of the individual ionic species is correlated to the local structure in the corresponding ionic liquid, namely the nano-segregation into polar and non-polar domains. In agreement with previous results, we observe that for relatively short alkyl chains the cations diffuse faster than the anions; however we also note that this difference becomes less evident for longer alkyl chains and a cross-over is identified at n ≈ 8 with the anions diffusing faster than the cations. Our results indicate that this controversial behavior can be rationalized in terms of different types of cation-cation and anion-anion orderings, as revealed by a detailed analysis of the correlation lengths and their dispersion curves obtained from SAXS data. We also discuss the validity of the Stokes-Einstein relation for these ionic liquids and the evolution of the extrapolated cationic radius that was found to depend non-strictly linearly on n, in agreement with the cation-cation correlation lengths. © 2013 the Owner Societies. Source

Kunz W.,University of Regensburg | Zemb T.,CNRS Marcoule Institute for Separative Chemistry | Harrar A.,University of Regensburg
Current Opinion in Colloid and Interface Science

Microemulsions are stable mixtures of a polar solvent, surfactant and an unpolar solvent. Ionic liquids (ILs, i.e. salts with melting points below 100°C) are a huge class of potentially promising solvents. We discuss here published structural or thermodynamic investigations concerning microemulsions in which one or more of the three classical components are ILs.In microemulsions IL can replace respectively the "oil", the "surfactant" and the "water" phase. Experimental proofs of the existence and stability of microemulsions are given as well as hints at their microstructure. While the four regimes initially defined by Winsor are all accessible, most of the examples of microemulsions containing ionic liquids belong to the class of "rigid" microemulsions. Since additional solutes have characteristic distribution coefficients for each pseudo phase, IL based microemulsions may provide a useful tool for solubilization (reaction medium) and separation, thus allowing the recovery of a large variety of reaction products, but also waste. Further to a discussion of phase diagrams and thermodynamics, we will show some application examples and propose challenges for future studies, in this vast but only emerging domain. © 2012 Elsevier Ltd. Source

Cau C.,CNRS Marcoule Institute for Separative Chemistry | Nikitenko S.I.,CNRS Marcoule Institute for Separative Chemistry
Ultrasonics Sonochemistry

The present work analyses the mechanism of W 2C/C nanocomposite formation during sonolysis of W(CO) 6 in diphenylmethane (DPhM) solutions. Carbon supported WC x nanoparticles attract much interest as an alternative fuel cell electrocatalysts. Sonolysis of neat DPhM under the effect of 20 kHz power ultrasound in argon at 80°C yields a sonopolymer as a solid product and acetylene, hydrogen, methane, diacetylene and benzene as gaseous products. Diacetylene is formed due to the secondary sonochemical dimerisation of acetylene obtained at the primary stage of DPhM sonolysis. FTIR and μ-Raman studies show that the sonopolymer consists of a mixture of some polymeric partially oxidized aromatic species, and disordered carbon. Sonolysis of W(CO) 6 in diphenylmethane solutions follows the first order kinetics. This process yields monodispersed 2-3 nm X-ray amorphous WC x nanoparticles embedded in amorphous sonopolymer. The annealing of air sensitive as-prepared solids in an inert atmosphere at 600°C causes formation of stable W 2C/C nanocomposite with W 2C average particle size in the range of 4-7 nm and hexagonal carbon fine particles with the average size of 30-40 nm. Kinetic study revealed that tungsten carbide is formed inside the cavitation bubble due to the reaction of tungsten nanoparticles originated from primary sonolysis of W(CO) 6 with acetylene produced as a result of diphenylmethane sonochemical degradation. © 2011 Elsevier B.V. All rights reserved. Source

Chave T.,CEA Marcoule Nuclear Site | Chave T.,CNRS Marcoule Institute for Separative Chemistry | Frugier P.,CEA Marcoule Nuclear Site | Gin S.,CEA Marcoule Nuclear Site | Ayral A.,Montpellier University
Geochimica et Cosmochimica Acta

The effect of calcium on synthetic glass alteration mechanisms has been studied. It is known that the higher the calcium content in the glass, the higher the forward rate. However, in a confined medium reaching apparent saturation state and a pH90°C around 9, synthetic calcium-bearing glasses are those with the lowest alteration rates. This work brings new and fundamental evidence toward understanding the alteration mechanisms: the rate-decreasing effect of calcium exists even if the calcium comes from the solution. Calcium from solution reacts with silica network in the hydrated layer at the glass surface. The calcium effect on the alteration kinetics is explained by the condensation of a passivating reactive interphase (PRI) whose passivating properties are strongly enhanced when calcium participates in its construction. These experiments provide new evidence of the role of condensation mechanisms in glass alteration. This better understanding of the calcium effect on glass long-term behavior will be useful both for improving glass formulations and for understanding the influence of the water composition. © 2011 Elsevier Ltd. Source

Discover hidden collaborations