Yaël Israëli

Intercalation of dicarboxylate anions into a Zn–Al–Cl layered double hydroxide: microcalorimetric determination of the enthalpies of anion exchange

The enthalpies of anion exchange in a chloride-intercalated zinc aluminium layered double hydroxide (LDH) in suspension in water have been studied at 25 °C. The heat effects associated with the exchange of the chloride anions for dicarboxylate anions (oxalate, succinate, adipate and tartrate) have been determined by titration microcalorimetry for different amounts of LDH. Except for tartrate, the exchange processes are endothermic, in contrast to the exchange processes involving only inorganic anions. The enthalpies of exchange vary linearly with the number of carbon atoms, suggesting that the intercalated dicarboxylate anions are perpendicular to the layers. The energetic parameters show, for the first time, hydrophobic interactions between the CH2 groups of the parallel succinate or adipate anions and hydrogen bonding between the OH groups of the parallel tartrate anions.

Photo-oxidation of polydimethylsiloxane oils: II—Effect of vinyl groups

Abstract The photo-oxidations, at wavelengths longer than 300 nm, of polydimethylsiloxane (PDMS) oils with various contents of vinyl and different configurations (vinyl in the polymer chain (3·1 and 7·1 wt % vinyl) or at the end of the chain of a low-molecular-weight compound (29 wt % vinyl)) have been examined. During irradiation, in the presence of oxygen, competition between scission and oxidation reactions occurs. Chain scissions represent the main reaction as expected from GC-MS analysis of a low-molecular-weight compound oxidation and from the evaluation of oxidized products, which represent only about 20% of the consumption of vinyl groups. The main oxidation products detected by FTIR spectroscopy are silanol (3475 cm −1 ), carboxylic acids (1717–1724 cm −1 ) and ester (1737 cm −1 ). An oxidation mechanism based on a radical addition to the double bond as initiation process is proposed to explain the formation of oxidized groups.

Thermodynamics of anion exchange on a chloride-intercalated zinc–aluminum layered double hydroxide: a microcalorimetric study

The thermodynamic properties of anion exchange on a chloride-intercalated zinc–aluminium layered double hydroxide have been studied at 298.15 K. The heats for total exchange of Cl− for F−, Br−, I−, OH−, NO3−, and SO42− have been determined by microcalorimetry and the standard molar enthalpies of these exchange reactions have been estimated. For the processes involving OH− and NO3−, the exchange isotherms have been determined using potentiometry in the former case and capillary ion analysis in the latter. The standard molar Gibbs free energy and entropy changes upon exchange of Cl− for OH− and exchange of Cl− for NO3− have been calculated as a function of the fraction of exchanged Cl−. These exchange processes appear to be entropy-driven, but the selectivity is controlled by the enthalpic contribution.

Photo-oxidation of polydimethylsiloxane oils: Part I—Effect of silicon hydride groups

Abstract Photo-oxidations at wavelengths longer than 300 nm of polydimethylsiloxane (PDMS) oil with various contents of SiH and different configurations (H inside the chain (2·2 H equivalent kg−1) or at the end of the chain (1·2–4 and 15 H equivalent kg−1)) have been examined. Hydroperoxides groups are primarily formed on photo-oxidation and result from radical attack on the SiH bond. These photo-unstable and thermally unstable hydroperoxides are transformed essentially into silanols, absorbing at 3300 cm−1. Oxygen consumption measurements suggest a 1 1 stoichiometry between SiH and oxygen consumed, whereas the quantitative determination of SiOH reveals a deficit, mainly as a result of a condensation reaction which leads to a significant increase in viscosity.

Structure of a Discrete 8:6 La(Iii): P-Sulfonatocalix[4]Arene Complex

Abstract The crystal structure of a complex formed between La(III) and p-sulfonatocalix[4]arene is reported. The complex cristallizes in the monoclinic space group P21/n, a = 15.091(1), b = 28.550(3), c = 30.167(3) Å, β = 90.008(2)°, V = 12997(2) Å3, ρcalc. (g cm−3) = 1.792, Z = 2. Refinement led to R1 value of 0.0961 for 13930 unique reflections. It forms discrete units with 8 La(III) cations coordinated by 6 calixarene ligands. The calixarenes are organized in an up-down configuration, bridged by La(III), forming layers of 3 repeating calixarene units and channels along the a axis. The units are linked by hydrogen-bonds.

Complexation of trivalent lanthanide cations by sugars and alditols in water: chromatography calorimetry comparison

Abstract A systematic study of the relative stabilities of the complexes formed between polyhydroxy compounds (sugars and alditols) and the trivalent lanthanide

Photo-oxidation of polydimethylsiloxane oils Part III—effect of dimethylene groups

Abstract Photo-oxidations at wavelengths longer than 300 nm of polydimethylsiloxanes (PDMS) formed by hydrosilylation reactions (i.e. containing dimethylene (∼CH2CH2∼) and methine groups) have been examined. The consumption of initial functional groups and the appearance of new groups derived from the photo-oxidation were followed by FTIR, 1H, 13C and 29Si NMR and GC/MS. The main photo-oxidation process is the hydroperoxidation of dimethylene groups and the photoscission of hydroperoxide groups into β-silylated carboxylic acid (∼SiCH2COOH) and silanol groups (SiOH). A small part of the silanols formed is condensed into ester and siloxane groups.

Free Energy Calculations in Electroactive Self-Assembled Monolayers (SAMs): Impact of the Chain Length on the Redox Reaction

The free energy approach is used to study the effect of the relative chain length of the two constituents of electroactive self-assembled monolayers (SAMs) on gold. In this study, the ferrocene groups are exposed to the electrolyte solution. This situation is achieved by using shorter diluent alkanethiol chains. To this end, the mixed monolayers formed by the self-assembly of 11-ferrocenylundecanethiol and butanethiol FcC(11)S/C(4)S and of 6-ferrocenylhexanethiol and butanethiol FcC(6)S/C(4)S onto a gold surface are studied. Calculation of enthalpy and entropy differences are also performed using molecular simulations. Additionally, the electrochemical signatures of these systems are determined to allow a direct comparison with our calculations. The thermodynamic properties are discussed in terms of enthalpy and entropy changes. Two effects account for the thermodynamic behavior. The first one involves the ion pairing between the ferrocenium group and the perchlorate anion. The second one concerns the desolvation of the first hydration shell of the anions. Finally, this work is also completed with a microscopic description associated with an energy characterization of these SAMs as a function of the surface coverage under conditions close to experiments.

Influence of CdSe/ZnS quantum dots in the polymerization process and in the grating recording in acrylate materials.

The initiation step of the polymerization of acrylate materials is first studied in detail by UV-visible spectroscopy, showing the involvement of each species of the three-component photosensitizer. Then, the implementation of a combined holographic and physicochemical investigation approach is used to determine the influence of photoluminescent CdSe/ZnS quantum dots (QDs) in the photopolymerization and grating recording process in composites containing those QD nanoparticles. The fluorescence microscopy evidences the dynamic distribution profile of QDs due to their diffusion from the irradiated zones to the interface between the bright and the dark zones and, finally, their accumulation in nonirradiated zones. At the same time, the infrared spectroscopy shows that the presence of QDs provides a noticeable decrease of the polymerization rate, which favors the diffusion of the monomer and QDs. These two phenomena contribute to the enhancement of the refractive index modulation depth.

Photooxidation of polydimethylsiloxane oils and resins. IV—effect of phenyl groups

Abstract Photooxidations at wavelengths longer than 300 nm of polydimethylsiloxane (PDMS) containing various contents of MePh and Ph 2 groups have been examined, both in the case of linear and crosslinked silicones. FTIR, UV and fluorescence spectroscopies reveal a slow photooxidation involving both scission and oxidation of the phenyl ring. No significant yellowing can be associated with the presence of the phenyl ring except in the case of short wavelength irradiation.