On the determination of equilibrium surface tension values of surfactant solutions

By using values ofdσ/dt as criterion for the establishment of the adsorption equilibrium great errors can result for strong surface active substances (gG_x/a?10^?2 cm). A simple linear extrapolation from curves σ or (σ₀-σ)^?1 on 1/√t (results of dynamic surface tension measurements) can lead to greater errors, too. Conditions are given under which the application of such extrapolation procedures is only possible. To get accurate equilibrium surface tension values of solutions of very strong surfactants (Γ_x/a>10^?1 cm) an extrapolation-interpolation algorithm based on adsorption-desorption measurements is suggested.     

Structure of the CO bond on supported Pd particles: influence of size and surface state

We have investigated the surface of supported palladium particles by static secondary ion mass spectrometry (SSIMS). Pd particles were grown in situ on alumi na (oxide layer and sapphire surfaces) and stabilized by heating treatment. The particle size, density and crystallographic structure were determined in previous studies by transmission electron microscopy and diffraction (TEM and TED). Various ionic species are detected by SSIMS analysis which makes it possible to characterize the CO absorbed layer: Pd _n CO⁺ (n=1, 2) for molecular adsorption and Pd _n C⁺ for CO dissociation. The size dependence of the bonding state of CO (linear, bridge, ...) was monitored by: PdCO⁺/σ _n Pd _n CO⁺ signal ratio over various size particles (mean diameter in the 2–9 nm range). Investigations were performed as a function of CO coverage (adsorption at room temperature) and also under CO dissociation conditions: heating under CO atmosphere or CO+O₂ (catalysis). The data analysis shows that on clean Pd particles smaller than 3 nm the CO molecules give rise mainly to PdCO⁺ species. We have interpreted this result by the adsorption of CO on two palladium atoms, the carbon end being tightly bonded to a low coordination Pd atom and the oxygen end weakly bonded to a neighbour Pd atom. These couples of Pd atoms form the specific sites for CO dissociation, the density of which depends on the roughness of the particle surface.     

Highly accurate and simple analytical approach to nonlinear Poisson–Boltzmann equation

A novel method is suggested to analytically solve a nonlinear Poisson–Boltzmann (NLPB) equation. The method consists chiefly of reducing the NLPB equation to linear PB equation in several segments by approximating a free term of the NLPB equation by piecewise linear functions, and then, solving analytically the linear PB equation in each segment. Superiority of the method is illustrated by applying the method to solve the NLPB equation describing a colloid sphere immersed in an arbitrary valence and mixed electrolyte solution; extensive test indicates that the resulting analytical expressions for both the electrical potential distribution Ψ (r) and surface charge density/surface potential relationship (σ/Ψ ₀) are characterized with two properties that mathematical structures are much simpler than those previously reported and application scope can be arbitrarily wide by adjusting the linear interpolation range. Finally, it is noted that the method is “universal” in that its applications are not limited to the NLPB equation.     

Acidic and reductive dissolution of magnetite in aqueous sulfuric acid: Site-binding model and experimental results

The open circuit dissolution of ionic metal oxides in mineral acids is modelled assuming that the rate is controlled by the transfer of metal ions in hydrolytic equilibrium with bulk metal ions, from the metal oxide surface to the Stern plane. The site-binding model of the double layer metal oxide/electrolyte solution is used to obtain the pH dependence of surface and Stern potentials. The nature of the active sites is discussed and their surface concentration is assumed to be proportional to suface charge σ₀. Again, the site-binding model is used to detemine the pH dependence of σ₀. It is thus shown that the rate order in c_H⁺ is essentially defined by the potential dependence of the charge transfer process, for oxides with points of zero charge near neutrality that dissolve in mildly or strongly acidic solutions. The role of surface complexation is also discussed in terms of the site-binding model and the difficulties in interpreting dissolution experiments under constant external applied potential are discussed in terms of the complexity of the semiconductor oxide/electrolyte solution interfacial region in magnetite.An experimental study of the open circuit dissolution of magnetite in sulfuric acid is presented and interpreted according to the proposed model.The reductive dissolution of magnetite is modelled by extension of the Valverde-Wagner model of oxide dissolution. Experimental results are presented to demonstrate that the reductive dissolution rate of magnetite in ferrous containing solutions is controlled by the rate of electron transfer from adsorbed Fe(II) to Fe(III) surface states of magnetite.     

Specific ion effects on the surface tension and surface potential of aqueous electrolytes

The phenomena of electrolytes affecting the surface tension of aqueous solutions and producing measurable surface potentials are reviewed in the light of recent studies of them. The factual information presented includes the molar ionic surface tension increments k_i = lim(c_i → 0)(dσ / dc_i) of many ions and the surface potential increments ∆ χ = χ_E − χ_W of electrolytes involving the cations H⁺, Na⁺, K⁺, and NH₄⁺ and various anions. Gaps in the data that invite filling and inconsistencies in reported data are pointed out. Correlations of k_i with several properties of the ions that should be relevant to their specific effects: their sizes, quantities representing their polarizabilities, their effects on the structure of the water and the binding of water molecules by them, are presented. Correlations of the surface potential increment ∆ χ with the electrolyte surface tension increments and with the differences between the cation and anion increments are shown. Models recently proposed for the rationalization of the observed phenomena and relevant theoretical developments are shown and discussed. The paradox of hydrogen ions not promoting significant charge separation at the interface but yielding large surface potentials is emphasized.     

Synthesis and surface chemistry of nano silver particles

In this report, we present a simple wet chemical route to synthesize nano-sized silver particles, and their surface properties are discussed in detail. Silver nano particles of the size 40–80 nm are formed in the process of oxidation of glucose to gluconic acid by amine in the presence of silver nitrate, and the gluconic acid caps the nano silver particle. The presence of gluconic acid on the surface of nano silver particles was confirmed by XPS and FTIR studies. As the nano silver particle is encapsulated by gluconic acid, there was no surface oxidation, as confirmed by XPS studies. The nano silver particles have also been studied for their formation, structure, morphology and size using UV–Visible spectroscopy, XRD and SEM. Further, the antibacterial properties of these nano particles show promising results for E. Coli. The influence of the alkaline medium towards the particle size and yield was also studied by measuring the pH of the reaction for DEA, NaOH and Na₂CO₃.     

Analysis of kinetic models for the tunnel electron transfer reactions. Reaction kinetics for various radial and angular dependences of the tunneling probability

A new version of the “stepwise” approximation used in kinetic models for the long range electron transfer reactions is suggested. Using this approach the effects on the kinetics of these reactions of such factors are examined as a more complicated dependence (compared to the commonly used exponential one) of the tunneling probability, w, on the distance between the reagents as well as the angular dependence of w. For many practically important situations taking account of the above factors is shown to have no significant effect on the form of the reaction kinetics for both the pairwise and random spatial distributions of the reagents. However, the relations between the parameters a_ef and ν_cf in the expression for the tunneling distance R* = ₂¹a_ef In ν_cft, which can be determined from the experimental kinetics, and similar theoretical parameters ν_o and a that are involved in the expressions for w are found to be different for various types of the radial and the angular dependences of w. It is shown that when the orbitals between which the electron transfer takes place are located at sites removed from the geometric centers of the reactants the values of ν_ef can exceed by many orders of magnitude the characteristic frequency of the electron movement in molecules ν_e ≈ 10¹³ s^?1.     

Densities,surface tensions,and derived surface thermodynamics properties of (trimethylbenzene + propyl acetate,or butyl acetate) from T = 298.15 K to 313.15 K

Densities (ρ) for binary systems of (1,2,4-trimethylbenzene, or 1,3,5-trimethylbenzene + propyl acetate, or butyl acetate) were determined at four temperatures (298.15, 303.15, 308.15, and 313.15) K over the full mole fraction range. The excess molar volumes (V^E) calculated from the density data show that the deviations from ideal behaviour in the systems (all being positive, excepting 1,2,4-trimethylbenzene + butyl acetate system) become more positive with the temperature increasing. Surface tensions (σ) of these binary systems were measured at the same temperatures (298.15, 303.15, 308.15, and 313.15) K by the pendant drop method, the surface tension deviations (δσ) for all system are negative, and decrease with the temperature increasing. The V^E and δσ are fitted to the Redlich–Kister polynomial equation. Surface tensions were also used to estimate surface entropy (S_σ) and surface enthalpy (H_σ).     

Thermoelectric properties of polycrystalline La1−xSrxCoO3

Thermoelectric properties of polycrystalline La_1−xSr_xCoO₃, where Sr²⁺ is substituted in La³⁺ site in perovskite-type LaCoO₃, have been investigated. Sr-doping increases the electrical conductivity (σ) of La_1−xSr_xCoO₃, and also decreases the Seebeck coefficient (S) for 0.01?x?0.40. A Hall coefficient measurement reveals that the increase in electrical conductivity arises from increases in both carrier concentration and the Hall mobility. The decrease in the Seebeck coefficient is caused by a decrease in carrier effective mass as well as increase in carrier concentration. The highest power factor (σS²) is 3.7×10⁻⁴ W m⁻¹ K⁻² at 250 K for x=0.10. The thermal conductivity (κ) is about 2 W m⁻¹ K⁻¹ at 300 K for 0?x?0.04, and increases for x?0.05 because of an increase in heat transport by conductive carrier. The thermoelectric properties of La_1−xSr_xCoO₃ are improved by Sr-doping, and the figure of merit (Z=σS² κ⁻¹) reaches 1.6×10⁻⁴ K⁻¹ for x=0.06 at 300 K (ZT=0.048). For heavily Sr-doped samples, the thermoelectric properties diminish mainly because of the decrease in the Seebeck coefficient and the increase in thermal conductivity.     

Excess thermodynamic functions derived from densities and surface tensions of (p- or o-xylene + ethylene glycol dimethyl ether) between the temperatures (298.15 and 308.15) K

Densities (ρ) for binary systems of (p-xylene or o-xylene + ethylene glycol dimethyl ether) were measured over the full mole fraction range at the temperatures of (298.15, 303.15 and 308.15) K along with the densities of the pure components. The excess molar volumes (V^E) calculated from the density data show that the deviations from ideal behaviour in the two binary systems are negative, and they become more negative with the temperature increasing. Surface tensions (σ) of these binary systems were determined at the same temperatures (298.15, 303.15 and 308.15) K by the pendant drop method. The surface tension deviations (δσ) for p-xylene system are negative over the whole composition range, and become less negative with the temperature increasing, but for the o-xylene system, δσ are negative at high o-xylene concentration, and change to positive with the o-xylene concentration decreasing. The V^E and δσ were fitted to the Redlich–Kister polynomial equation. Surface tensions were also used to estimate surface entropy (S_σ) and surface enthalpy (H_σ).     

Cationic iridium complexes of the Xantphos ligand. Flexible coordination modes and the isolation of the hydride insertion product with an alkene

Reaction of the Ir(I)-Xantphos complex [Ir(κ²-Xantphos)(COD)][BAr^F₄] (Xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene, Ar^F = C₆H₃(CF₃)₂) with H₂ in acetone or CH₂Cl₂/MeCN affords the Ir(III)-hydrido complexes [Ir(κ³-Xantphos)(H)₂(L)][BAr^F₄], L = acetone or MeCN, whereas in non-coordinating CH₂Cl₂ solvent dimeric [Ir(κ³-Xantphos)(H)(μ-H)]₂[BAr^F₄]₂ is formed. A common intermediate in these reactions that invokes a (σ, η²-C₈H₁₃) ligand is reported. Addition of excess tert-butylethene (tbe) to [Ir(κ³-Xantphos)(H)₂(MeCN)][BAr^F₄] results in insertion of a hydride into the alkene to form [Ir(κ³-Xantphos)(MeCN)(CH₂CH₂C(CH₃)₃)(H)][BAr^F₄], an Ir(III) alkyl-hydrido-Xantphos complex. This reaction is reversible, and heating (80 °C) results in the reformation of [Ir(κ³-Xantphos)(H)₂(MeCN)][BAr^F₄] and tbe. These complexes have been characterised by NMR spectroscopy, ESI-MS and single-crystal X-ray diffraction. They show variable coordination modes of the Xantphos ligand: cis-κ²-P,P, fac-κ³-P,O,P and mer-κ³-P,O,P with the later coordination mode like that found in related PNP-pincer complexes.     

Tetrachloroferrate (III) Salts of BDH-TTP [2,5-Bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene] and BDA-TTP [2,5-Bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene]: Crystal Structures and Physical Properties

Three FeCl₄ salts based on non-tetrathiafulvalene (TTF) donors, 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene (BDH-TTP) and 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene (BDA-TTP), have been prepared and characterized as κ-(BDH-TTP)₂FeCl₄, β-(BDA-TTP)₂FeCl₄, and (BDA-TTP)₃FeCl₄ · PhCl. The κ-(BDH-TTP)₂FeCl₄ salt, with a room-temperature conductivity (σ_rt) of 39 S cm⁻¹, is metallic down to 1.5 K, and its magnetic susceptibility obeys the Curie-Weiss law with a Curie constant (C) of 4.25 emu K mol⁻¹ and a Weiss constant (θ) of 0.041 K. β-(BDA-TTP)₂FeCl₄ exhibits metallic behavior (σ_rt=9.4 S cm⁻¹) with a sharp metal-to-insulator (MI) transition (T_MI=113 K) and antiferromagnetic ordering with the Néel temperature of near 8.5 K, whereas the solvated (BDA-TTP)₃FeCl₄ · PhCl salt is a semiconductor with a thermal activation energy of 0.11 eV (σ_rt=2.0× 10⁻² S cm⁻¹) and exhibits Curie-Weiss behavior (C=4.42 emu K mol⁻¹, θ=−0.35 K).     

Adsorption of ions in the diffuse part of an electrical double layer at ionic surfactant solution-air interfaces in the presence of background electrolytes

The equations are derived for the calculation of adsorption values Γ _± ^d of coions and counterions in the diffuse part of an electrical double layer characterized by Ψ_d potential in the presence of a background electrolyte. The case of arbitrary |Ψ_d| values is considered. Based on the known experimental data, the contributions of adsorption values Γ _± ^d to the surface excesses of ions, as determined by the Gibbs method for the solution-air interfaces, are quantitatively estimated. It is shown that the adsorption of counterions in the diffuse part of the electrical double layer is significantly lower than that in its dense part; however, the orders of these values are comparable. At potentials |Ψ_d| > 25 mV, surface-active ions are mainly located near the interface, and their adsorption values Γ _? ^d cannot noticeably affect the calculated surface excesses.     

The stability of hydrophobic sols in the presence of surface active agents

Summary The stability of Thorium dioxide sols at p_H=3.5 was examined as a function of anionic surface active agents spectrophotometrically. At low concentrations of surface active agents, the stability of the sol decreases and attains a minimum value at concentrations 10⁻⁴ to 10⁻³ M. With increasing concentration the stability increases and attains a maximum at concentrations 10⁻³ to 10⁻² M. The effect of the P_H-value, the chain length and the head groups of the surface active agents are also studied. The results were explained on the basis of strong adsorption of these ions at the Stern plane.     

On the evaluation of non-adiabatic coupling matrix elements for large scale CI wavefunctions

The implementation of a recently proposed technique for evaluating matrix elements of the form 〈Ψ_J(r;R)|∂Ψ_I(r;R)/t6R_α〉_r using analytic gradient techniques is described. The Ψ_K(r;R) are developed from state-averaged multiconfiguration self-consistent-field/configuration interaction (CI) wavefunctions. The CI wavefunctions are determined using the shape driven graphical unitary group approach. The method is shown to be considerably more efficient than presently existing approaches based on divided differences. As an illustration of the potentialities of this approach non-adiabatic coupling matrix elements are determined for the collinear charge transfer reaction: Mg(¹S) + FH(¹Σ⁺)→MgF(²Σ⁺)+H(²S).     

Estimating resonance enhancement of Raman scattering by metal adatom-adsorbate complexes

Publications on surface-enhanced Raman scattering (SERS) in metal sols are perused. The discrepancy between extinction spectra for freshly formed sols and the SERS excitation spectra is found to be connected with different temperature modes used in different procedures for obtaining sols, the temperature difference leading to different concentrations of metal adatoms on sol particles. Once the presence of adatoms is accounted for, the nature of “hot” sol particles, which ensure the observation of values of the SERS enhancement coefficient G?10¹⁴?10¹⁵, can be explained and the reasons for the scarcity of such particles can be established. On compact hot sol particles, rigorous calculations of electromagnetic enhancement G _em in most cases yield G _em≤ 10¹⁴. That is why combining the coefficient σ_b of gigantic amplification of background, which is caused by electron RS in metal and which is connected with the existence of adatoms, with the coefficient σ_si of SERS enhancement in a metal-metal adatom-adsorbate adsorption complex gives σ_bσ_si ≥ 10⁸.     

Experimental and theoretical studies of the valence-shell dipole excitation spectrum of molecular fluorine

Electron energy loss measurements and concommitant RPAE calculations are reported of the valence-shell dipole excitation spectrum of molecular fluorine. The measured spectrum is dominated by a series of strong features in the 12–16 eV interval which are in accord with X¹Σ_g⁺→¹Σ_u⁺ bands assigned in a previously reported high-resolution optical study. These features are attributed on basis of the present RPAE calculations to configuration mixing between 1π_g→npπ_u Rydberg and 3σ_g→3σ_u intravalence excitations. A depleted X→V_σ charge-transfer excitation is correspondingly observed at ≈17 eV, in good accord with the calculated values. The appearance of the σ→σ* transition in F₂ below the 3σ_g^?1 threshold is in marked contrast to the situation in other light diatomic molecules, in which cases σ→σ* transitions appear as intravalence shape resonances in photoionization continua. Assignments are also provided of weak, irregularly spaced X¹Σ_g⁺→¹Π_u excitations the origins of which are attributed to configuration mixing between 1π_g→npσ_u and 1π_u→nsσ_g Rydberg series.     

The diffusion of methane in inorganic membrane pores under Knudsen conditions: the kinetics and depth of pyrocarbon deposition and its influence on transport properties

The kinetics of the topochemical reaction of methane dehydrogenation was studied using TRUMEM ultrafiltration membranes (TiO₂ + Cr₂O₃ on porous steel, the size of transport pores 50 nm). The depth of the deposition of pyrocarbon nanocrystallites (PNC) into pores was determined. The depth of PNC deposition was estimated using scanning electron microscopy and high-resolution energy-dispersion spectrometry. The deposition of PNC at a 4.9 kPa methane pressure in the reaction zone created Knudsen conditions for methane diffusion in pores. The deposition of PNC therefore occurred over the whole area of pore surfaces. Studies of the kinetics of PNC formation on the surface of pores showed that reaction rate V and its constant k substantially depended on reaction duration. The influence of PNC deposition on the electrosurface properties and permeability of the membranes to ethanol and dodecane was studied. After the deposition of PNC with L _c = 1.0–1.1 nm on the surface of pores, the ζ-potential and surface charge density (σ) decreased; simultaneously, the efficiency with respect to ethanol increased.