Dilational viscoelasticity of anionic polyelectrolyte/surfactant adsorption films at the water–octane interface

In this article, the interfacial tension and interfacial dilational viscoelasticity of polystyrene sulfonate/surfactant adsorption films at the water–octane interface have been studied by spinning drop method and oscillating barriers method respectively. The experimental results show that different interfacial behaviors can be observed in different type of polyelectrolyte/surfactant systems. Polystyrene sulfonate sodium (PSS)/cationic surfactant hexadecanetrimethyl–ammonium bromide systems show the classical behavior of oppositely charged polyelectrolyte/surfactant systems and can be explained well by electrostatic interaction. In the case of PSS/anionic surfactant sodium dodecyl sulfate (SDS) systems, the coadsorption of PSS at interface through hydrophobic interaction with alkyl chain of SDS leads to the increase of interfacial tension and the decrease of dilational elasticity. For PSS/nonionic surfactant TX100 systems, PSS may form a sub-layer contiguous to the aqueous phase with partly hydrophobic polyoxyethylene chain of TX100, which has little effect on the TX100 adsorption film and interfacial tension.     

Flow microcalorimetry of adsorption of anionic alkyl surfactants at the solid/liquid interface

Flow microcalorimetry was used to study the adsoption of anionic alkyl surfactants from aque--ous solutions onto silica. It is found that for alkyl sulfate systems the strength of adsorption interactionincreases with increases of the alkyl chain length and decreases as temperature rises. The adsorptiondepends only on monomer concentration of the solution even above the critical micelle concentration(cmc). The assumption is made that the adsorption involves only a transfer of monomers from bulkto surface phase. A different adsorption mechanism is operative for the alkyl carboxylate.     

Ion transfer across the immiscible water—o-nitrotoluene interface

The standard Gibbs energies of transfer of some ions across the immiscible water—o-nitrotoluene interface have been determined voltammetrically. These values are compared with the theoretical values calculated using a model of ionic solvation.     

Estimation of spinodals from the density profile of the vapor–liquid interface

An extension of a recently proposed method for the calculation of the spinodals in pure fluid systems from the interfacial properties is elaborated, which requires the density profile as only input. The foundation of this approach is the so-called Fuchs-transformation which gives an estimate for the tangential pressure profile from the density profile. Using molecular dynamics simulation data for argon and carbon dioxide as well as lattice Boltzmann simulation data for the argon-like Shan–Chen fluid, the accuracy of the approach is analyzed. The Fuchs-transformation is qualitative, however it is possible to estimate the temperature–density projection of the spinodal. Depending on the underlying correlation function for the interfacial density profile reasonable results are obtained for the liquid and the vapor spinodal. The advantage of this method is that equilibrium data can be used to estimate the spinodal which is experimentally impossible to access because it is a highly non-equilibrium property. In the final consequence of this approach only the coexistence vapor and liquid densities are required to estimate the temperature–density projection of the spinodals.     

Charge transfer across the water/nitrobenzene interface by three-electrode system

A droplet of aqueous solution containing a certain molar ratio of redox couple is first attached onto a platinum electrode surface, then the resulting drop electrode is immersed into the organic solution containing very hydrophobic electrolyte. Combined with reference and counter electrodes, a classical three-electrode system has been constructed. Ion transfer (IT) and electron transfer (ET) are investigated systematically using three-electrode voltammetry. Potassium ion transfer and electron transfer between potassium ferricyanide in the aqueous phase and ferrocene in nitrobenzene are observed with potassium ferricyanide/potassium ferrocyanide as the redox couple. Meanwhile, the transfer reactions of lithium, sodium, potassium, proton and ammonium ions are obtained with ferric sulfate/ferrous sulfate as the redox couple. The formal transfer potentials and the standard Gibbs transfer energy of these ions are evaluated and consistent with the results obtained by a four-electrode system and other methods.     

Molecular dynamics simulation of surfactant effects on ion transport through a liquid–liquid interface between partially miscible liquids

Molecular dynamics (MD) simulations of water + 1-hexanol + NaCl mixtures with and without a surfactant (methanol) were performed to analyze the surfactant's effect on the transport of a sodium ion through the liquid–liquid interface. Without surfactant, the 1-hexanol forms a bilayer at the interface with OH groups directed outward toward the aqueous phase. Addition of the surfactant produces higher concentrations of the surfactant on the aqueous side of the interface without altering the organic bilayer structure. An electrical double-layer is created in both cases as chloride ion concentration is enhanced near the interface and sodium ion concentration is enhanced toward the center of the water phase. A potential of mean force (PMF) was calculated for the transfer of a sodium ion through the interface. Although the surfactant reduced the interfacial tension, the total work required for the ion transfer increased with the addition of the surfactant.     

Molecular structure of mixed adsorption layers surfactant—polymer at a liquid—liquid interface

Isotherms of the binding of dodecyl sulfate anions (DDS^–)and Na⁺ counterions during their coadsorption with a nonionic polymer. proxanol (PR). at the interface of dodecane-water emulsions have been measured by conductometry and Na-selective potentiometry. The adsorption of DDS^– and PR is concurrent. The affinity constant of PR to the interface determined by the Langmuir model decreases as the concentration of PR increases, and the surface concentration of DDS^– tends to a nonzero limiting value at high concentrations of PR. The surface (_o) and electrokinetic () potentials at the interface have been determined at various polymer concentrations by the spin probe and electrophoresis methods. The average dielectric permeability and density of polymer segments in We adsorption layer have been determined by ESR. The lower boundary of the hydrodynamic thickness of the polymer adsorption layer at the interface has been estimated from the dependences of _o and on the ionic strength.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1653–1661, July, 1996.     

Onsager heat of transport at the aniline liquid–vapour interface

The heat of transport for passage of matter through a gas–liquid interface has been determined for the aniline liquid–vapour system, by measuring stationary-state pressure differences produced by known temperature differences over a distance of 2 mm on the vapour side of the interface. For the range of pressures used, 2 mm is between 6 and 34 mean free paths. Coupling of the heat and matter fluxes is significant over the whole of this range. At the higher pressures the heat of transport is more than 20% of the heat of condensation; at the lower pressures it is more than 50%.     

A.c. voltammetric evidence for the transient adsorption of asymmetric ions in the transfer across the nitrobenzene–water interface

A.c. impedance studies of the ion transfer have evidenced the transient adsorption of xanthene-type anions and other ions having asymmetric charge distribution at the nitrobenzene–water interface. The phase angle of the charge transfer admittance becomes smaller than unity at the potentials beyond the midpoint potential of the ion transfer. This anomaly does not appreciably depend on the sign of the ionic charge or the location of the midpoint potential, as predicted by the theory proposed recently based on the thermodynamic reasoning of the adsorption and ion partitioning of surface active ions in electrochemical liquid–liquid two-phase systems [T. Kakiuchi, J. Electroanal. Chem. 496 (2001) 137].     

Chronopotentiometric and voltammetric study of cesium ion transfer across the water—1,2-dichloroethane interface

Results of electrochemical studies of the cesium ion transfer reaction from water to 1,2-dichloroethane (1,2-DCE) for low ion concentration are presented. Measurements have been made by chronopotentiometric and cyclic voltammetry methods. The diffusion coefficient of Cs⁺ in water saturated with 1,2-DCE and the half wave potential of Cs⁺ at the water—1,2-DCE interface have been determined.     

Combined scanning electrochemical microscopy–Langmuir trough technique for investigating phase transfer kinetics across liquid/liquid interfaces modified by a molecular monolayer

The first combination of scanning electrochemical microscopy (SECM) with a Langmuir trough for liquid/liquid interfaces is described. The technique has been examined and demonstrated through investigations of the effect of monolayers of l-α-phosphatidylcholine, distearoyl (DSPC) on the kinetics of oxygen transfer from decane to water. The stability of monolayers, formed in this way, on the timescale of SECM measurements has been identified as a function of compression speed and subphase composition. Monolayers were stable over a wide range of pressures and molecular areas, but at high compression a decrease in surface pressure with time was observed. This effect was attributed to desorption of the lipid from the interface. In this situation, it was possible to perform SECM measurements (tip-interface approach curves) rapidly under surface pressure control, without causing significant disturbance to the monolayer. DSPC had no detectable effect on the oxygen transfer kinetics when the monolayer was in the liquid-expanded phase, but in the liquid-condensed phase a significant decrease in the rate of oxygen transfer was observed.     

Solid–liquid interface analysis with in-situ Rutherford backscattering and electrochemical impedance spectroscopy

A novel Rutherford backscattering spectrometry (RBS) method is presented to investigate the interface between a solid surface and a surrounding liquid. The introduced measurement system allows to observe and quantify adsorption at the solid–liquid interface and the formation of the electrochemical double layer (EDL). BaCl₂ as a bicomponent electrolyte and a Si₃N₄ membrane surface are chosen as a model system to prove the capabilities of the setup. The results of these RBS measurements are combined with electrochemical impedance spectroscopy (EIS) to validate the findings for the solid–liquid interface under study. Complementary results and discrepancies regarding the formation of the EDL are discussed.     

Dynamic properties of the polyethylene glycol molecules on the oscillating solid–liquid interface

The dynamic properties of polyethylene glycol (PEG) molecules on the solid–liquid interface oscillating at MHz were investigated using the quartz crystal microbalance (QCM). The number-average molecular weights (M_n) of the PEG molecules were systematically varied over 4 orders of magnitude. This study makes it clear that the series-resonant frequency shift, ΔF, of the QCM against the square root of the density–viscosity product of the PEG solution is linear and has the intercept. Moreover, systematical analysis reveals that the ΔF slope rapidly decreases with M_n and that the ΔF intercept becomes constant above 4.0 × 10³ g mol⁻¹. As a result, those reveal that the resonant length of the PEG molecule moving with the oscillating plate of 9 MHz is 54.2 Å. We also find that the behaviors of ΔF due to M_n are mainly caused by the length of the PEG molecule.     

Voltammetric determination of perchlorate ion at a liquid–liquid microscopic interface

A method is proposed for the electrochemical determination of perchlorate ion by voltammetry at the interface between two immiscible phases (water–o-nitrophenyl octyl ether). A demountable original-design amperometric ion-selective electrode based on a laser-microperforated polymeric membrane was fabricated for voltammetric measurements. The conditions of analytical signal recording in the determination of ClO₄ ^? were determined. The effect of interfering ions was assessed and amperometric selectivity coefficients were calculated. The accuracy of the procedure was verified by the added–found method. The developed electrode was applied to the determination of perchlorate in natural and drinking waters.     

Electrosynthesis of polyphenylpyrrole coated silver particles at a liquid–liquid interface

This communication reports the production of polyphenylpyrrole coated silver nanoparticles at the liquid/liquid interface by an EC-type mechanism. In the electrochemical step of the reaction N-phenylpyrrole facilitates the transfer of the silver ion from an aqueous to an organic phase. This step is followed by a slow homogeneous electron transfer reaction from the N-phenylpyrrole to the silver ion followed by polymerization and metal cluster growth.     

Systematic study of the transfer of amino acids across the water/1,2-dichloroethane interface facilitated by dibenzo-18-crown-6

Facilitated ion transfer reactions of 20 amino acids with dibenzo-18-crown-6 (DB18C6) at the water/1,2-dichloroethane (W/DCE) interfaces supported at the tips of micro- and nano-pipets were investigated systematically using cyclic voltammetry. It was found that there were only 10 amino acids, that is, Leu, Val, lie, Phe, Trp, Met, Ala, Gly, Cys, Gin (in brief), whose protonated forms as cations can give well-defined facilitated ion transfer voltammograms within the potential window, and the reaction pathway was proven to be consistent with the transfer by interfacial complexation/dissociation (TIC/TID) mechanisms. The association constants of DB 18C6 with different amino acids in the DCE (β0), and the kinetic parameters of reaction were evaluated based on the steady-state voltammetry of micro- or nano-pipets, respectively. The experimental results demonstrated that the selectivity of complexation of protonated amino acid by DB18C6 compared with that of alkali metal cations was low, which can be attribu     

Charge transfer characteristics of F6TCNNQ–gold interface

The metal–organic interface between polycrystalline gold and hexafluorotetracyanonaphthoquinodimethane (F₆TCNNQ) was investigated by photoelectron spectroscopy with the focus on the charge transfer characteristics from the metal to the molecule. The valence levels, as well as the core levels of the heterojunction, indicate a full electron transfer and a change in the chemical environment. The changes are observed in the first F₆TCNNQ layers, whereas for further film growth, only neutral F₆TCNNQ molecules could be detected. New occupied states below the Fermi level were observed in the valence levels, indicating a lowest unoccupied molecular orbital (LUMO) occupation due to the charge transfer. A fitting of the spectra reveals the presence of a neutral and a charged F₆TCNNQ molecules, but no further species were present.