Review on Some Confusion Produced by the Bicontinuous Microemulsion Terminology and Its Domains Microcurvature: A Simple Spatiotemporal Model at Optimum Formulation of Surfactant-Oil-Water Systems.

Fundamental studies have improved understanding of molecular-level properties and behavior in surfactant-oil-water (SOW) systems at equilibrium and under nonequilibrium conditions. However, confusion persists regarding the terms "microemulsion" and "curvature" in these systems. Microemulsion refers to a single-phase system that does not contain distinct oil or water droplets but at least four different structures with globular domains of nanometer size and sometimes arbitrary shape. The significance of "curvature" in such systems is unclear. At high surfactant concentrations (typically 30 wt % or more), a single phase zone has been identified in which complex molecular arrangements may result in light scattering. As surfactant concentration decreases, the single phase is referred to as a bicontinuous microemulsion, known as the middle phase in a Winsor III triphasic system. Its structure has been described as involving simple or multiple surfactant films surrounding more or less elongated excess oil and water phase globules. In cases where the system separates into two or three phases, known as Winsor I or II systems, one of the phases, containing most of the surfactant, is also confusedly referred to as the microemulsion. In this surfactant-rich phase, the only curved objects are micellar size structures that are soluble in the system and have no real interface but rather exchange surfactant molecules with the external liquid phase at an ultrafast pace. The use of the term "curvature" in the context of these complex microemulsion systems is confusing, particularly when applied to merged nanometer-size globular or percolating domains. In this work, we discuss the terms "microemulsion" and "curvature", and the most simple four-dimensional spatiotemporal model is proposed concerning SOW equilibrated systems near the optimum formulation. This model explains the motion of surfactant molecules due to Brownian movement, which is a quick and arbitrary thermal fluctuation, and limited to a short distance. The resulting observation and behavior will be an average in time and in space, leading to a permanent change in the local microcurvature of the aggregate, thus changing the average from micelle-like to inverse micelle-like order over an extremely short time. The term "microcurvature" is used to explain the small variations of globule size and indicates a close-to-zero mean curvature of the surfactant-containing film surface shape.

Isoselenocyanates versus Isothiocyanates and Isocyanates.

Alkyl and aryl isoselenocyanates are well known intermediates in the synthesis of various organoselenium compounds, but the knowledge of the physicochemical properties of simple unsaturated derivatives is still fragmentary. Vinyl-, 2-propenyl-, and cyclopropyl isoselenocyanates have been prepared by reaction of selenium in powder with the corresponding isocyanides. The isoselenocyanates of this series, with a variable distance between the N═C═Se group and the unsaturated or pseudounsaturated group, have been studied by UV-photoelectron spectroscopy and quantum-chemical calculations. For each of these three isoselenocyanates, the exploration of conformers and geometrical optimization always converge toward only one local minimum. The vinyl and cyclopropyl derivatives are characterized by similar order of magnitude of interactions between the NCSe group and the substituent, while for allylic compound two noninteracting moieties should be considered. The same conclusions were obtained for vinylic and cyclopropylic sulfur and oxygen derivatives. Thus the type and extent of interactions between the N═C═X (X = O, S, Se) group and an unsaturated (vinyl, allyl, or cyclopropyl) moiety are now clarified.

Electronic structure of BN-aromatics: Choice of reliable computational tools.

The importance of having reliable calculation tools to interpret and predict the electronic properties of BN-aromatics is directly linked to the growing interest for these very promising new systems in the field of materials science, biomedical research, or energy sustainability. Ionization energy (IE) is one of the most important parameters to approach the electronic structure of molecules. It can be theoretically estimated, but in order to evaluate their persistence and propose the most reliable tools for the evaluation of different electronic properties of existent or only imagined BN-containing compounds, we took as reference experimental values of ionization energies provided by ultra-violet photoelectron spectroscopy (UV-PES) in gas phase-the only technique giving access to the energy levels of filled molecular orbitals. Thus, a set of 21 aromatic molecules containing B-N bonds and B-N-B patterns has been merged for a comparison between experimental IEs obtained by UV-PES and various theoretical approaches for their estimation. Time-Dependent Density Functional Theory (TD-DFT) methods using B3LYP and long-range corrected CAM-B3LYP functionals are used, combined with the ΔSCF approach, and compared with electron propagator theory such as outer valence Green's function (OVGF, P3) and symmetry adapted cluster-configuration interaction ab initio methods. Direct Kohn-Sham estimation and "corrected" Kohn-Sham estimation are also given. The deviation between experimental and theoretical values is computed for each molecule, and a statistical study is performed over the average and the root mean square for the whole set and sub-sets of molecules. It is shown that (i) ΔSCF+TDDFT(CAM-B3LYP), OVGF, and P3 are the most efficient way for a good agreement with UV-PES values, (ii) a CAM-B3LYP range-separated hybrid functional is significantly better than B3LYP for the purpose, especially for extended conjugated systems, and (iii) the "corrected" Kohn-Sham result is a fast and simple way to predict IEs.

Two BN isosteres of anthracene: synthesis and characterization.

The synthesis of two parental BN anthracenes, 1 and 2, was developed, and their electronic structure and reactivity behavior were characterized in direct comparison with all-carbon anthracene. Gas-phase UV-photoelecton spectroscopy studies revealed the following HOMO energy trend: anthracene, -7.4 eV; BN anthracene 1, -7.7 eV; bis-BN anthracene 2, -8.0 eV. The λmax of the lower energy band in the UV-vis absorption spectrum is as follows: anthracene, 356 nm; BN anthracene 1, 359 nm; bis-BN anthracene 2, 357 nm. Thus, although the HOMO is stabilized with increasing BN incorporation, the HOMO-LUMO band gap remains unchanged across the anthracene series. The emission λmax values for the three investigated anthracene compounds are at 403 nm. The pKa values of the N-H proton for BN anthracene 1 and bis-BN anthracene 2 were determined to be approximately 26. BN anthracenes 1 and 2 do not undergo heat- or light-induced cycloaddition reactions or Friedel-Crafts acylations. Electrophilic bromination of BN anthracene 1 with Br2, however, occurs regioselectively at the 9-position. The reactivity behavior and regioselectivity of bromination of BN anthracenes are consistent with the electronic structure of these compounds; i.e., (1) the lower HOMO energy levels for BN anthracenes stabilize the molecules against cycloaddition and Friedel-Crafts reactions, and (2) the HOMO orbital coefficients are consistent with the observed bromination regioselectivity. Overall, this work demonstrates that BN/CC isosterism can be used as a molecular design strategy to stabilize the HOMO of acene-type structures while the optical band gap is maintained.

UV-photoelectron spectroscopy of BN indoles: experimental and computational electronic structure analysis.

We present a comprehensive electronic structure analysis of two BN isosteres of indole using a combined UV-photoelectron spectroscopy (UV-PES)/computational chemistry approach. Gas-phase He I photoelectron spectra of external BN indole I and fused BN indole II have been recorded, assessed by density functional theory calculations, and compared with natural indole. The first ionization energies of these indoles are natural indole (7.9 eV), external BN indole I (7.9 eV), and fused BN indole II (8.05 eV). The computationally determined molecular dipole moments are in the order: natural indole (2.177 D) > fused BN indole II (1.512 D) > external BN indole I (0.543 D). The λmax in the UV-vis absorption spectra are in the order: fused BN indole II (292 nm) > external BN indole I (282 nm) > natural indole (270 nm). The observed relative electrophilic aromatic substitution reactivity of the investigated indoles with dimethyliminium chloride as the electrophile is as follows: fused BN indole II > natural indole > external BN indole I, and this trend correlates with the π-orbital coefficient at the 3-position. Nucleus-independent chemical shifts calculations show that the introduction of boron into an aromatic 6π-electron system leads to a reduction in aromaticity, presumably due to a stronger bond localization. Trends and conclusions from BN isosteres of simple monocyclic aromatic systems such as benzene and toluene are not necessarily translated to the bicyclic indole core. Thus, electronic structure consequences resulting from BN/CC isosterism will need to be evaluated individually from system to system.

UV-photoelectron spectroscopy of 1,2- and 1,3-azaborines: a combined experimental and computational electronic structure analysis.

We present a comprehensive electronic structure analysis of structurally simple BN heterocycles using a combined UV-photoelectron spectroscopy (UV-PES)/computational chemistry approach. Gas-phase He I photoelectron spectra of 1,2-dihydro-1,2-azaborine 1, N-Me-1,2-BN-toluene 2, and N-Me-1,3-BN-toluene 3 have been recorded, assessed by density functional theory calculations, and compared with their corresponding carbonaceous analogues benzene and toluene. The first ionization energies of these BN heterocycles are in the order N-Me-1,3-BN-toluene 3 (8.0 eV) < N-Me-1,2-BN-toluene 2 (8.45 eV) < 1,2-dihydro-1,2-azaborine 1 (8.6 eV) < toluene (8.83 eV) < benzene (9.25 eV). The computationally determined molecular dipole moments are in the order 3 (4.577 D) > 2 (2.209 D) > 1 (2.154 D) > toluene (0.349 D) > benzene (0 D) and are consistent with experimental observations. The λ(max) in the UV-vis absorption spectra are in the order 3 (297 nm) > 2 (278 nm) > 1 (269 nm) > toluene (262 nm) > benzene (255 nm). We also establish that the measured anodic peak potentials and electrophilic aromatic substitution (EAS) reactivity of BN heterocycles 1-3 are consistent with the electronic structure description determined by the combined UV-PES/computational chemistry approach.

Are unsaturated isocyanides so different from the corresponding nitriles?

Simple unsaturated and cyclopropylic isocyanides are synthesized by an efficient and simple approach. These compounds with gradually increasing distance between the unsaturated moiety and the isonitrile group are studied by UV photoelectron spectroscopy and quantum chemical calculations, and also compared to the corresponding nitriles. The first photoelectron band of the unsaturated compounds is linked to removal of an electron from the HOMO, which corresponds to CC multiple-bond ionization in antibonding interaction with the π-isocyanide bond (in the same plane) for conjugated systems, or in antibonding interaction with the pseudo-π-CH(2) group for isolated systems. For the 1-ethenyl derivatives, both cyano and isocyano groups act as a π-electron acceptor from the vinyl group, but the isocyano π system is much more strongly destabilized (ionization energies (IEs) shift to smaller values) by vinyl (3.12 eV) than the cyano π system is (2.70 eV). In comparison with the 1-ethynyl derivatives, a less pronounced destabilization (2.69 eV) of π(NC) by the ethynyl system (1.86 eV for π(CN)), and nearly the same order of magnitude of the energetic gap between the total antibonding (π(CC)-π(NC)) and the total bonding (π(CC)+π(NC)) IEs for ethenyl and ethynyl compounds are noted. The huge values of these last-named data for H(2)C=CH-NC (3.85 eV) and for HC≡C-NC (4.04 eV) reflect the strong interaction between the unsaturated carbon-carbon moiety and the isocyanide group, and thus more efficient conjugation than for the corresponding nitriles.

Strong specific hydroxide ion binding at the pristine oil/water and air/water interfaces.

Despite claims, based largely on molecular dynamics simulations, that the surface of water at the air/water interface is acidic, with a positive charge, there is compelling experimental evidence that it is in fact basic, with a negative charge due to the specific adsorption of hydroxide ions. The oil/water interface behaves similarly. The pH dependence of the zeta potentials of oil drops has been measured by two very different techniques: on a single drop in a rotating electrophoresis cell and on about 10(14) submicrometer drops in a 2 vol % emulsion by an electroacoustic method to give similar results with a sigmoidal pH dependence characterized by an isoelectric point at pH 2-3 and a half adsorption point about pH 5.5, or at 10(-8.5) M hydroxide ion. This indicates that hydroxide ion is absorbed much more strongly than other anions. The pH dependence of a single N(2) bubble has also been measured and has the same pH dependence, independently of whether HCl or HI is used to adjust the pH. These similarities between the pH dependences of the zeta potentials of air bubbles and oil drops, as well as those reported from streaming potentials on solid inert surfaces such as Teflon, indicate that water behaves similarly, with only subtle differences, at each of these low dielectric hydrophobic surfaces, with an isoelectric point of pH 2-4. In acidic solutions at pH's below the isoelectric point, the surface is indeed positive, consistent with spectroscopic observations of the adsorption of hydrogen ions.

Beta-heterosubstituted acrylonitriles--electronic structure study by UV-photoelectron spectroscopy and quantum chemical calculations.

Beta-heterosubstituted acrylonitriles correspond to the formal addition of nucleophiles on cyanoacetylene. Acrylonitriles substituted with an amino, methoxy, mercapto group, or halogeno atom have been synthesized. Rearrangements between Z and E stereoisomers or tautomerizations have been studied by NMR spectroscopy and by quantum calculations. The photoelectron spectra were recorded and analyzed with the aid of a time-dependent density functional theory, ab initio OVGF, and so-called "corrected" ionization energy calculations. The electronic structure of the studied species was determined, and strong differences between beta-heterosubstituted acrylonitriles and the corresponding nitrile-free heteroalkenes were clearly documented. A "push-pull" effect was noticed, due to the combined donor effect of the substituent on one side of the carbon-carbon double bond and the electron-withdrawing effect of the nitrile group on the other side. Thus, the presence of a nitrile group strongly stabilizes the electronic structure. The efficient pi-donor contribution of the NH(2) and SH groups was evidenced.

Methylidynearsine (HC[triple bond]As): synthesis and direct characterization by UV-photoelectron spectroscopy and mass spectrometry.

The dehydrohalogenation of gaseous dichloromethylarsine on solid base led to chloromethylidenearsine and, at higher temperature of the base, to methylidynearsine, the third unsubstituted heteroalkyne unambiguously synthesized up to now.

The selective partitioning of the oligomers of polyethoxylated surfactant mixtures between interface and oil and water bulk phases.

Because their affinities for the oil and water phases vary considerably with the number of ethylene oxide units in their hydrophilic group, the ethoxylated nonionic species occurring in commercial products tend to behave in a non-collective way, with the low ethoxylation oligomers partitioning mostly in the oil phase. This results in a surfactant mixture at the interface which is more hydrophilic than the one which was introduced in the system in the first place. The pseudophase model is used to study the partitioning in Winsor III type systems, and to estimate the deviation of the interfacial mixture composition from the overall one. New results indicate that the selective partitioning into the oil phase increases when the oil phase becomes aromatic, when the total surfactant concentration decreases and when the water-to-oil ratio decreases.

Stability of water/crude oil emulsions based on interfacial dilatational rheology.

The dilatational viscoelasticity behaviors of water/oil interfaces formed with a crude oil and its distilled fractions diluted in cyclohexane were investigated by means of an oscillating drop tensiometer. The rheological study of the w/o interfaces at different frequencies has shown that the stable w/o emulsions systematically correspond to interfaces which present the rheological characteristics of a 2D gel near its gelation point. The stability of emulsions was found to increase with both the gel strength and the glass transition temperature of the gel. As expected, the indigenous natural surfactants responsible for the formation of the interfacial critical gel have been identified as the heaviest amphiphilic components present in the crude oil; i.e., asphaltenes and resins. Nevertheless, we have shown that such a gel can also form in the absence of asphaltene in the oil phase.

Modeling heating curve for gas hydrate dissociation in porous media.

A method for modeling the heating curve for gas hydrate dissociation in porous media at isochoric conditions (constant cell volume) is presented. This method consists of using an equation of state of the gas, the cumulative volume distribution (CVD) of the porous medium, and a van der Waals-Platteeuw-type thermodynamic model that includes a capillary term. The proposed method was tested to predict the heating curves for methane hydrate dissociation in a mesoporous silica glass for saturated conditions (liquid volume = pore volume) and for a fractional conversion of water to hydrate of 1 (100% of the available water was converted to hydrate). The shape factor (F) of the hydrate-water interface was found equal to 1, supporting a cylindrical shape for the hydrate particles during hydrate dissociation. Using F = 1, it has been possible to predict the heating curve for different ranges of pressure and temperature. The excellent agreement between the calculated and experimental heating curves supports the validity of our approach.

Properties of a two-dimensional asphaltene network at the water-cyclohexane interface deduced from dynamic tensiometry.

Static and dynamic tensiometries show that a newly prepared water/asphaltenated cyclohexane interface behaves as expected: the mean area occupied per asphaltene molecule is 2 nm2, and variations of interfacial tension and dilatational elastic modulus with time indicate that equilibrium is reached more slowly than that for usual surfactants. The use of the time/temperature superposition principle allows a detailed rheological study of a 2 day old interface of the same type which has reached equilibrium. It is found that the two-dimensional asphaltene network exhibits a glass transition zone, behaves as a gel near its gelation point, and is built by a universal process of aggregation.