Mise au point d'un appareillage de preparation et de manipulation de melanges anhydres HFNH3MF (M alcalin) — tension de vapeur totale au-dessus de solutions HFNH3 riches en HF

An apparatus for preparing and handling HFNH₃MF mixtures (M alkali metal) has been designed and constructed. The vacuum line made of plastic materials (PVF₂, PTFCE, PTFE) allows the purification of anhydrous hydrogen fluoride, preparation and analysis of HFNH₃ or HFNH₃MF mixtures and their handling for further study or destruction.Total vapour pressures above HFNH₃ binary mixtures rich in HF have been measured and are described as a function of ammonia concentration and temperature (?10 to +20°C).     

Some New Data for Metal Desorption on Inorganic-Organic Hybrid Materials

A 2(4-1) fractional factorial design is employed to study Cu(II) desorption on organofunctionalized silicas. Two types of silicas, at amounts of 100 and 200 mg and two acidic levels, and contact times were employed. Our study indicates that the effects of HCl and contact time on the percentage number of moles of copper are 13.23 and 18.53, respectively. However, the binary interaction of these factors is very small. Three important antagonistic and synergistic binary effects involving the silica type, acidic quantity, and contact time factors are found. The silica mass showed an insignificant principal effect. The desorption data are compared with those previously published concerning adsorption processes on both functionalized silicas. Copyright 2000 Academic Press.     

Shapes and dynamics of miscible liquid/liquid interfaces in horizontal capillary tubes

We report optical observations of the dissolution behaviour of glycerol/water, soybean oil/hexane, and isobutyric acid (IBA)/water binary mixtures within horizontal capillary tubes. Tubes with diameters as small as 0.2mm were initially filled with one component of the binary mixture (solute) and then immersed into a solvent-filled thermostatic bath. Both ends of the tubes were open, and no pressure difference was applied between the ends. In the case of glycerol/water and soybean oil/hexane mixtures, we managed to isolate the dissolution (the interfacial mass transfer) from the hydrodynamic motion. Two phase boundaries moving from the ends into the middle section of the tube with the speeds v～D(1/3)t(-2/3)d(2) (D,t and d are the coefficient of diffusion, time and the diameter of the tube, respectively) were observed. The boundaries slowly smeared but their smearing occurred considerably slower than their motion. The motion of the phase boundaries cannot be explained by the dependency of the diffusion coefficient on concentration, and should be explained by the effect of barodiffusion. The shapes of the solute/solvent boundaries are defined by the balance between gravity and surface tension effects. The contact line moved together with the bulk interface: no visible solute remained on the walls after the interface passage. Changes in temperature and in the ratio between gravity and capillary forces altered the apparent contact angles. The IBA/water system had different behaviour. Below the critical (consolute) point, no dissolution was observed: IBA and water behaved like two immiscible liquids, with the IBA phase being displaced from the tube by capillary pressure (the spontaneous imbibition process). Above the critical point, two IBA/water interfaces could be identified, however the interfaces did not penetrate much into the tube.     

Monte Carlo simulation for the formation of a mixed crystal from two solids in contact

The study focuses on nucleation and growth of a binary mixed crystal phase from two pure crystals in contact. Monte Carlo simulations of this process are conducted, with the dynamics proceeding via activated atom-vacancy exchanges. Intermolecular interactions, ranging up to next-nearest neighbors, are of size typical of hydrogen bonded systems. The process is driven by the formation of strong AB bonds at the expense of weaker AA and BB bonds. In the resulting model, the material is channeled and transported through the mixed phase crust along antiphase boundaries. The flow of molecules through the channels is directed, due to molecular energy lowering via gradual acquisition of an increasing number of nearest neighbors of the second species. On the other hand, defect motion is quasirandom. The model accounts partially for the t(1/alpha) (alpha>3) time dependence observed for conversion of nanoparticles of HBr dihydrate to monohydrate, by exposure to acid adsorbate.     

Diffusion-controlled solid-state reactions of spherical particles, a general model for multiphase binary systems

The formal treatment of the diffusion-controlled growth of n binary compounds with narrow homogeneity range during the reaction of a sphere of reactant A immersed in reactant B is presented and discussed. Both constituents are assumed to be mobile. The reaction products are assumed to grow simultaneously as uniform and compact concentric layers with ideal contact at the interfaces as well as at the external surface of the sphere. The kinetic equations follow from the coupling between chemical reactions and partitioning of the diffusion flux at phase boundaries. The results for the formation of two and three compounds are presented. The influence of the initial radius of the sphere, of the relative magnitude of the kinetic constants, and of the volume variation is discussed in detail.     

Influence de la solvatation par le tert-butanol sur la structure et la reactivite de l'enolate de potassium de l'acetylacetate d'ethyle en presence de couronne ou de cryptand. etude par spectrometrie infra-rouge et cinetique

The structure and the nucleophilic reactivity of crowned (18-crown-6) or cryptated {cryptand (2.2.2)} potassium ethyl acetoacetate enolate have been compared in tert-butanol and in DME (or THF). In the protic solvent tert-butanol, the crowned and the cryptated potassium enolate species both exist as loose ion pairs in which the enolate anion, strongly hydrogen-bonded to the solvent, is in a “transoid” (non chelating) conformation. Both species show similar reactivities towards alkylating agents but completely different reactivities are observed in aprotic weakly dissociating media (THF, DME). In contrast to what is observed in tert-butanol, the cryptated species and the crowned species have very different nucleophilic reactivities in THF or DME; in those solvents only the cryptated species retains a loose ion pair structure; the crowned species is a contact ion pair in which the enolate anion chelates the potassium cation. The solvation of this crowned chelate species by tert-butanol has been demonstrated in binary mixtures of solvents (C₆D₆-t-BuOH, THF-t-BuOH). The oxygen basicity of the enolate anion is very different in the crowned chelated ion pair compared with the cryptand separated ion pair.     

Utilisation de l'ultracentrifugeuse pour la mesure des masses et pour l'etude de la polydispersite des polymeres de synthese

After a review of the two techniques based on sedimentation rate and equilibrium in binary medium, more recent methods involving the presence of a second non-macromolecular solute are described. Application of these methods to synthetic polymers is still rare but of increasing interest. The use of computers simplifies the exploitation of the measurements.     

Etude de la reactivite de lion azoture vis á vis de cations heterocycliques-IV comportement vis á vis de cations chromylium diversement substitues. Rearrangement thermique des azides covalents obtenus. Voie originale d'acces aux benz[f]heteroazepines

The study of the azide nucleophile reaction with substituted chromylium salts is presented. When heated, the azido 2H-and azido 4H-chromenes obtained give benz(f)oxazepins in very good yields. This is an easy preparation of these compounds.     

Evaporation of microdroplets of ethanol-water mixtures on gold surfaces modified with self-assembled monolayers

The wetting property and evaporation behavior of ethanol-water mixtures of various concentrations on gold surfaces modified with 1-decanethiolate self-assembled monolayers (SAMs) were studied by digital contact angle analysis. It has been shown that the initial contact angle decreases monotonically with increased concentration of ethanol in the mixture. Evaporation studies revealed a general trend with a preliminary increase in contact angle accompanied with a decrease in contact area, then a constant contact angle accompanied with a slower, linear decrease in contact area. At the very beginning of the evaporation process, the contact angles showed a rapid decrease for the microdroplets of a binary mixture with equal volume fractions (i.e., 50% ethanol). Three distinct stages of the evaporation profile for the ethanol-water mixtures were observed, which differ from the inclusive "pinning" and "shrinking" behavior observed for the pure liquid case. Ultimately, the study makes possible the use of an evaporation profile to monitor the change in concentration of a binary system and allows a better understanding of the interactions between liquid microdroplets with solid substrates.     

A quantitative experimental study of wetting hysteresis on discrete and continuous chemical heterogeneities

Chemically heterogeneous surfaces are well known to induce contact angle hysteresis due to the local energy barriers that oppose contact line movement. In many cases, the surface heterogeneity is discontinuous, i.e. discrete regions of different wettability exist, which leads to pinning of the contact line at boundaries between regions. Pinning on individual rows of microscopic defects arranged in a square lattice can be sensed using a Wilhelmy balance to reveal discrete stick-slip motion. For defects more wettable than the matrix with a lattice spacing of 28 μm, the advancing contact line slips over ～10 rows in a single slip step, while the receding contact line stick-slips between individual rows of defects. Single, millimetre-scale defects were used to assess the energy involved when a contact line advances or recedes over a hydrophilic (more wettable) defect. Quantitative information about defect-induced hysteresis in relation to defect dimensions is obtained. The crucial importance of wetting boundaries is highlighted with an experimental example of a surface that is heterogeneous yet, due to the continuously changing pattern, does not exhibit contact angle hysteresis.     

Bis(imidazolylidene)s as modular building blocks for monomeric and macromolecular organometallic materials

The synthetic and structural progression surrounding N-heterocyclic carbenes has given rise to great functional and architectural diversity in organometallic chemistry, catalysis, and materials science. The development of new, modular scaffolds for bridging transition metals is essential in order to expand the boundaries of these scientific areas. This Frontier article summarizes recent advances in the synthesis and study of ditopic ligands displaying two linearly opposed carbene moieties and emphasizes their versatility in the preparation of new organometallic and macromolecular materials. The conclusion previews their utility in conjugated organic/inorganic hybrid materials with potential applications in the emerging fields of molecular- and nanoelectronics.     

Equilibres liquide-vapeur isothermes de melanges binaires de la piperidine et de la N-methyl piperidine avec certains ethers

The authors have measured the vapour pressure of the binary four systems, piperidin +1,4-dioxan, piperidin+tetrahydropyran, piperidin+tert-butyl methyl ether and N-methyl piperidin+tert-butyl methyl ether. The measurements were carried out using an isoteniscope built by J. Jose [1]. The vapour pressure, excess Gibbs free energies at 298.15 K, 303.15 K, 313.15 K, 323.15 K, 333.15 K and 343.15 K, are reported for these mixtures. The excess Gibbs free energies have been fitted to the Redlich-Kister equation.     

Préparation de dérivés de sucres acétyléniques terminaux et d'acides ynuroniques par réaction de Wittig. Note de laboratoire

Synthesis of Terminal Acetylenic Sugars Derivatives and Ynuronic Acids Derivatives by Use of a Wittig Reaction The method described for the preparation of terminal acetylenic sugars presents two advantages over earlier procedures: no new asymmetric center is created and the chain can be extended by one or more C-atoms. The method also allows preparation of ynuronic acids. The aldehydosugars derivatives 1–7 gave in good to excellent yields the corresponding gem-dibromoenoses 8–14 from which either the terminal acetylenic sugars derivatives 15–21 or the ynuronic acids 22–24 were easily prepared. A few examples of 1,3-dipolar cycloadditions (leading to 28–30 ) with these acetylenic sugar derivatives are also described.     

Equilibres liquide-vapeur isothermes de melanges binaires de la piperidine et de la N-methyl piperidine avec certains ethers

The authors have measured the vapour pressure of the four binary systems, piperidine +tert-butyl methyl ether, piperidine +1,4 dioxane, piperidine + tetrahydropyrane and N-methyl piperidine +tert-butyl methyl ether. The measurements were carried out using an isoteniscope built by J. Jose [1], The vapour pressure, excess Gibbs free energies at 298.15, 303.15, 313.15, 323.15, 333.15 and 343.15 K, are reported for these mixtures. The excess Gibbs free energies have been fitted to the Redlich-Kister equation.

     

Application of power expansion in the thermodynamics of compressible Markovian copolymers

The problem of constructing phase diagrams for a compressible melt of a binary Markovian copolymer is reduced to a set of nonlinear differential equations in partial derivatives with transcendental relationships. Using power expansions, the closed set of nonlinear differential equations is derived. This set allows its further analytical study. Eigenvalues of a linearized system are analyzed, and the boundaries of the thermodynamic stability of melts are defined. Nonlinear equations in normal coordinates are obtained; for symmetric melts, these equations are reduced to a single equation by adiabatic elimination of small-scale variables. Binodal curves are calculated for such solutions of this equation, which correspond to the free energy minimum of melts. Corrections reflecting the effect of melt nonsymmetry are found. The results are applied for copolymers, whose composition is similar to that of homopolymers, diblock copolymers, and random and regularly alternating copolymers. Spinodals and binodals corresponding to microphase separation are constructed.     

Preparation d'homopolymeres du thietanne de masses moléculaires determinees

A study has been made of the polymerization of thietane by thiolates such as thia-3-pentane thiolate with sodium, potassium or tetraethylammonium as cation. The following solvents have been used: tetrahydrofurane, acetonitrile, hexamethylphosphorotriamide and dimethylsulphoxide. Such thiolates permit the preparation of homopolymers of thietane with specified molecular weights but it has not been possible to explain, in these reactions, the activity of sodium naphthalene at −78°. The relationship between number average molecular weight and intrinsic viscosity is given.     

Particles coming together: electron centers in adjoined TiO2 nanocrystals

To include particle attachment and porosity of nanostructured materials in the discussion of their electronic properties is critical to our understanding of charge transfer across grain boundaries. We report the condensation of isolated TiO(2) nanocrystals via the application of a simple hydration-dehydration cycle. After contact with water and subsequent removal of adsorbed water, these nanocrystals form a mesoporous structure with altered properties as compared with the original material: first, the energy needed for defect formation is substantially reduced, and second, electron paramagnetic resonance measurements reveal the presence of polarizable conduction band electrons not detectable in samples which have not been in contact with water.     

Phase equilibria in binary mixtures of ethane and hexadecane

This paper reports experimental results of a study of the phase behaviour of binary mixtures of ethane + hexadecane. In the near-critical region of ethane liquid + vapour and solid hexadecane + liquid two-phase boundaries have been measured. Also the three-phase equilibrium solid hexadecane + liquid + vapour has been determined experimentally. The experimental data cover the complete mole fraction range. Pressures up to 18 MPa were applied and the investigation was performed in a temperature region from about 260 K up to 450 K.     

Wetting of the container wall as a critical-point phenomenon. III. Wetting by contacting conjugate solutions of ternary systems

In the ternary systems benzene-ethanol-water and ethyl acetate-ethanol-water, the contact angles of the meniscus between two immiscible liquid phases (i.e., conjugate solutions) and a solid substrate tend toward 90° as compositions approach the consolute point at a constant temperature; just as, in a binary system, the contact angles between the corresponding three phases have been shown (in the previous paper of this series) to tend toward 90° as the temperature approaches the critical point. The quantitative expression for the variation of the contact angle with the concentration of the cosolvent in the vicinity of the consolute point in a ternary system also bears a formal mathematical resemblance to that found for the corresponding variation of the contact angle with temperature in a binary system.     

From molecules to aggregates

The preparation of organometallic oxides, imides and nitrides is described. The molecular structures of these compounds resemble those found in binary systems. However, due to the organic envelope of the molecular solids, they are soluble in organic solvents, easy to crystallize and unambiguously characterizable by single X-ray structural analysis and NMR investigations. Moreover, inorganic oxides can be incorporated in organometallic phosphonates or organoalumoxanes. Herein we describe the organometallic phosphonates as hosts with a hydrophobic exterior.