Properties of argon liquid-vapor interface

The short-wave cutoff boundary of the capillary wave spectrum is established. Effective thickness L _b of the “bare” density profile in the interfacial layer is calculated according to experimental data on the ellipticity ratio of reflected light. The free parameters of the extended van der Waals theory of capillarity are determined. The positions of the equimolecular dividing surface and tension surface are calculated, as well as the temperature dependence of the Tolman parameter.     

On the validity of certain integro-differential equations for the density—orientation profile of molecular fluid interfaces

The status of some recently proposed integro-differential equations for the density—orientation profile, p(r₁, ω₁), of non-uniform molecular fluids is examined. Two of the equations derived by Gubbins, which involve derivatives with respect to angular coordinates ω₁, are shown to be incorrect and corrected versions are proposed. The implications of the results for pairwise correlations and for the surface tension of the liquid—gas interface are discussed.     

Thermal and spectral properties and induction period, interfacial energy and nucleation parameters of solution grown anthracene

Anthracene crystals were grown by solution growth technique by adopting slow evaporation method from the solvents CS₂, CCl₄ and CHCl₃. The induction period was measured at various super saturations, and hence the interfacial energies were evaluated. Using the interfacial tension value, the nucleation parameters such as radius of the critical nuclei (r*), the Gibbs free energy change for the formation of a critical nucleus (?G*) and the number of molecules in the critical nucleus (i*) were also calculated for all these solvents at two different temperatures. The effect of surface tension, viscosity and density of these solvents are correlated with interfacial tension. The solution grown crystals were subjected to UV, FTIR, NMR and X-ray diffraction studies. The purity and high-thermal stability of the grown crystals were determined using thermal analysis.     

Correlation energy correction as a density functional. A model of the pair distribution function and its application to the first- and second-row atoms and hydrides

A scheme for correlation energy corrections E_c based on asymptotic properties of the effective pair distribution function g(r₁; r₂) and correlation energy densities ϵ_c{ϱ(r₁)} has been considered. To obtain ϵ_c{ϱ(r₁)} model functions g(r₁; r₂) are used in the local spin density approximation (LSDA). This model yields the correct high-density limit for the homogeneous electron gas ϵ_c{ϱ} and reproduces empirical E_c values with an average error amounting to 2.2% for the first- and second-row closed-shell atoms, 5.6% for the first-row hydrides XH and 3.4% for the second-row hydrides XH.     

Droplet coalescence near liquid/liquid critical points

The state of matter within a fluid layer near a critical point differs profoundly in many aspects from states further removed from the critical point. The interfacial tension tends to vanish, the interface thickens, and long-range concentration fluctuations exist. Because of these effects, critical phenomena have been investigated as possible sources of instability in thin films. Shear-field coalescence studies have been performed between phases of a simple ternary system containing no surfactant as a function of distance from a critical point. The coalescence efficiency was measured as a function of temperature through time dependent photomicrographic analysis of emulsion samples within a shear-field coalescence cell. The apparatus, procedure, and analysis are outlined. No evidence was found for the promotion of coalescence by critical phenomena for values of reduced temperature, T_r = (T − T_c)/T_c, down to 4×10⁻⁴.     

Topological studies on IRC paths of X+H2→XH+H reactions

Topological properties of potential energy and electronic density distribution on five reaction paths X+H₂→XH+H (X=H, N, HN, H₂C, NC) are investigated at the level of UMP2/6–311G(d,p). It has been found that in the region of the reaction paths studied, where B(r_c)|_s>0 [B(r_c)|_s is the product of ρ(r_c) and ∇²ρ(r_c) at the point of reaction process, i.e., B(r_c)|_s=ρ(r_c)∇² ρ(r_c)] is basically the same as the region of V′(s)<0[V′(s) is the second derivative of potential energy with respect to the reaction coordinate, i.e., V′(s)=d²V/ds²], and the point with maximum B(r_c)|_s is almost coincident with the point of minimum V′(s). It can be concluded from the calculated results that there is a good correlation between the topological properties of potential energy and electronic density distribution along the reaction path. The structure transition state of such collinear reactions may be determined by topological analysis of electronic density. © 1997 John Wiley & Sons, Inc. J Comput Chem 18: 1167–1174     

Lattice model for the surface region of solutions consisting of different-sized molecules with orientation effects

Smirnova, N.A., 1978. Lattice model for the surface region of solutions consisting of different-sized molecules with orientation effects. Fluid Phase Equilibria, 2: 1–25.A multilayer lattice model for the surface region of solutions consisting of different-sized molecules with orientation effects is developed. The system is treated in the grand canonical ensemble on the basis of the quasi-chemical approximation. The results relate to the mixtures of monomers + flexible r-mers, where all r segments of r-mer may be different and the surface of monomer molecules and r-mer segments may be inhomogeneous (thus, the systems with polar components, associated solutions among them, are in the range of applicability of the model). The monomer + r-mer system is described based on the modified model for the multicomponent system formed by monomeric particles with strong directed interactions. Equations for the concentration profile and for the average molecular orientations, with respect to the surface, are derived; the formulae for the adsorption and surface tension are given. The surface properties calculated on the basis of the model for three monomer + dimer systems are in satisfactory agreement with the experimental data. The entropy contribution to the surface tension of pure r-mer composed of identical segments is reported for r = 2, 4, 6, 8, 12 and for different lattice parameters. The model can be generalized to mixtures of r-mers + l-mers.     

Surface characteristics of polysulfoalkyl methacrylates

Coated hydroxyethyl methacrylate-sodium sulfoalkyl methacrylate copolymer films were surface characterized. The contact angle hysteresis increases and the receding angle decreases with increasing alkyl side-chain length, while the advancing angle decreases with hydration time. It was found that the buoyancy slopes of the advancing (r_a) and receding (r_r) process determined by the Wilhelmy plate method were not parallel. The ratio of r_a to r_r was greater than 1, and increases with the alkyl side-chain length and the hydration time, contrary to that of polyhydroxyethyl methacrylate, where r_a/r_r was less than 1. The slope ratio would be suppressed in solution with added salt, revealing that the reorientation and expansion of the polymer chain in water is being suppressed. X-ray photoelectron spectroscopy (XPS) analysis of the surface of these copolymers showed a striking enrichment of the sulfonate groups in the surface. The zeta potential was between −40 and −50 mV as measured by the streaming potential method. During dehydration, along with a decrease in sulfur and sodium concentration in the surface, the carbon 1s peak at the high binding energy decreased and the alkyl carbon main peak increased. The surface tension of aqueous solutions of sulfoalkyl methacrylate monomers and homopolymers decreases with increasing alkyl side-chain length, which may contribute to the decrease in water-polymer film interfacial tension and thus the increase in the slope ratio.     

Polyparaxylylene-CdS nanocomposite films: Optical spectra, photoluminescence, and surface topography

For polyparaxylylene-CdS nanocomposite films prepared by solid-phase cryochemical synthesis, the dependences of the optical absorption spectra, photoluminescence intensity, and surface topography on the CdS concentration were examined. It was revealed that the most significant changes, such as the shift of the position of the exciton absorption band by ～1 eV and the increase of the surface roughness (the magnitude of variation of heights h _max ? h _min along a surface profile) occur within a CdS concentration range of from ～5 to ～8 vol %. The average size of the nanoparticles was determined from the position of the exciton absorption maximum: 2R _np ? ? 3 nm at c ≤ 5 vol % and 2R _np ≥ 5?7 nm at c ≥ 10 vol %. The formation of 3-nm particles at low CdS concentrations was confirmed by the existence of exciton photoluminescence with maximum at 370 nm. Exciton luminescence was not observed at c ≥ 10 vol %. By contrast, at all c values, photoluminescence with maxima at ～520 and ～570 nm, which is usually assigned to interstitial S and Cd atoms, correspondingly, and a the weak emission of unknown nature with a maximum at 545 nm were observed.     

A study of sulfur homogeneous nucleation from supersaturated vapor. Determination of surface tension of sulfur nanoparticles

Homogeneous nucleation in sulfur vapor is studied in a laminar-flow chamber. Concentration and size distribution of resulting aerosol particles are measured with a diffusion spectrometer of aerosols and a PK.GTA-0,3-002 photoelectric particle counter. The crystal structure of the formed particles is studied by X-ray diffraction analysis. The rate of sulfur evaporation from a boat and the profile of a deposit on the chamber wall along the axial coordinate are determined by gravimetry. Axial and radial temperature profiles are measured using a chromel-alumel thermocouple. The vapor concentration distribution in the chamber is found and the supersaturation is calculated from the solution of the mass-transfer problem. An experimental low-laborious method is developed for the supersaturation cutoff. This method enables one to rapidly deter-mine the position of the zone in which the nucleation proceeds at the highest rate. The position of the zone of nucleation found by this method is in good agreement with the results of calculations based on experimental data and theoretical calculation of the rate of nucleation by an exact formula that has been recently derived based on the works by Kusaka and Reiss, as well as the Frenkel liquid kinetics theory. The surface tension of critical sulfur nuclei resulting from the nucleation is calculated based on this formula and experimental data on the nucleation. It is established that, in a temperature range of 312–319 K, the critical nuclei have tension surface radius R _s ～ 10.6 Å and surface tension σ = 72.5 ± 1.1 dyn/cm. The surface tension of critical sulfur nuclei in this temperature range is constant and approximately 5% higher than that of a planar surface.     

Evaluation of electron-hole recombination properties of titanium (IV) oxide particles with high photocatalytic activity

Electron-hole recombination in nano-sized titanium(IV) oxide (TiO₂) particles with various physical properties, which have been shown to be highly active photocatalysts, was evaluated by quantitative analysis of reduced titanium species (Ti³⁺), which might be formed at crystalline defective sites in TiO₂ particles through photo-irradiation in the presence of a hole scavenger under deaerated conditions. These highly active photocatalyst samples were synthesized by hydrothermal crystallization in organic media (HyCOM method) and post-calcination. The Ti³⁺ density decreased with increasing calcination temperature (T _c), and a linear correlation was observed between the Ti³⁺ density and rate constant for electron-hole recombination evaluated by femtosecond pump-probe diffuse reflection spectroscopy. Reaction rate (R _Ag) and the amount of silver ions (Ag⁺) adsorbed on TiO₂ particles ([Ag⁺]_ads) were measured for photocatalytic silver metal deposition along with oxygen formation from an aqueous Ag⁺ solution under deaerated conditions, and the slope of the R _Ag versus [Ag⁺]_ads plot was determined. Kinetic investigation of this reaction showed that the reciprocal of the slope was approximately related to the ratio of the rates for electron-hole recombination and electron trapping (k _r/k _e ratio). The k _r/k _e ratio decreased as T _c increased, and the logarithm of the k _r/k _e ratio was linearly related with Ti³⁺ density. These two parameters were used as a measure for the recombination properties of TiO₂ photocatalysts with various physical properties.     

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.     

The WCl6-e-Al-CH2Cl2 catalyzed polypentenamer formation via ring-opening metathesis polymerization (ROMP)

The synthesis of polypentenamer by an electrochemically generated metathesis polymerization catalyst from methylene chloride solution of WCl₆ was investigated. The active species formed by electroreduction of this salt under controlled potential of +900 mV at a platinum cathode with an aluminum anode were found to catalyze the ring-opening metathesis polymerization (ROMP) of cyclopentene, monocyclic olefin of relatively low strain, in high yield (89%) and at short period (32 min) under mild conditions. The effect of reaction parameters, e.g., olefin/catalyst ratio, reaction time, electrolysis time, catalyst aging, on the polymerization yield have been studied. The resulting polymer has been characterized by ¹H and ¹³C NMR, IR and gel permeation chromatography (GPC) techniques. Analysis of the polypentenamer microstructure by means of ¹³C NMR spectroscopy indicates that the polymer contains a mainly trans stereoconfiguration of the double bonds (σ_c = 0.31) and a slightly blocky distribution (r_tr_c > 1) of cis and trans double bond dyads (r_tr_c = 1.44). However, this electrochemical system is reluctant to facilitate the competing vinyl type addition polymerization reactions.     

Photocapacitance spectroscopy of thin film cadmium selenide electrodes

Photocapacitance spectroscopic measurements were made on thin film CdSe that was prepared by electrodeposition from a solution of selenosulfite and cadmium ions. The spectra were very similar for five spots on three films that were prepared under identical conditions. In 0.5 M KOH solution, the film appeared stable for a number of measuremens at various applied potentials. At pH 10 the film was relatively stable for applied potentials negative of 0.0 V (SCE). At more positive potentials in this solution, surface oxidation appears to occur, resulting in the formation of a surface layer that alters the spectrum. In both solutions, the photocapacitance spectrum appears independent of applied potential over the range employed. The continuous rise without any abrupt steps in the spectrum as the photon energy is increased indicated that there are probably a series of bandgap states of comparable density. The energy levels range from E_c − 1.1 eV to E_c − 1.6 eV. In contrast with thin film CdSe prepared by vacuum coevaporation, the electrodeposited material did not require low frequency (7 to 70 Hz) for the measurement.     

Effect of Low Temperature Air Plasma Treatment on Wetting and Flow Properties of Kaolinite Powders

It was found in this study that the air plasma treatment of particular kaolinite has led to the change of its wettability, which was reflected in the decreased values of water contact angles of wetting from 88.7° for virgin kaolinite to 86.3° for 30?min air plasma treated one. Plasma treated samples show higher average surface energies in the wide range of coverage regimes in comparison to the virgin samples as determined by inverse gas chromatography. Results of these measurements confirmed our assumption, that air plasma treatment activates surface energy of the crystal planes of the kaolinite as reflected in the broadened dispersive surface energy distribution after 10?min treatment time. However with prolonged 30?min treatment time the dispersive surface energy distribution profile was decreased. We assume, that the latter decrease reflects the distorsion of the crystal lattice of the kaolinite as confirmed by FTIR analysis as reflected in changes of Si?CO?CSi and Al₂O?CH characteristic absorption bands. Calculated dispersive surface free energy for 24?% surface coverage was increased from original 35?mJ/m² to 40.3 and 40.8?mJ/m² for 10 and 30?min treatment times. There were determined yield locus and flow function dependencies at different stress levels for virgin and different time plasma treated samples (flow index??ff _c , effective angle of internal friction???? _e , unconfined yield strength???? _c ). It was found that by plasma treatment the character of the flow was shifting from region of very cohesive (ff _c ?=?2.39) to the cohesive (ff _c ?=?3.19). For untreated samples effective angle of internal friction was decreased with increasing applied consolidation stress, while for plasma treated kaolinite it was increased.     

Optimum topographical and morphological information in AFM tapping mode investigation of multicomponent polyethylene

For systematic AFM tapping mode studies of a binary blend of multicomponent polyethylene height and phase images were recorded at different set-point amplitude ratios r_sp ranging from 0.95 to 0.1. Force-probe mode measurements were carried out both in stiff and soft regions of the blend. Based on the resulting amplitude/phase versus distance curves a contrast interpretation of the height and phase images at different r_sp was carried out. In agreement with the results of several authors it was demonstrated that only at light tapping, with r_sp close to 1, does the profile in the height image present a true surface topography, whereas with r_sp≈0.5 much harder tapping is necessary, so that maximum phase contrast is observed. Therefore, interleave scanning with lighter and harder tapping in the main and interleaved scans, respectively, was used to simultaneously record height and phase images with optimum topographical and morphological information, respectively. Furthermore, interleave scanning combined with negative lift mode was used to make local changes in indentation visible.     

Characterizing phase transitions in liquid cesium by a soft-core and large-attraction equation of state

This paper investigates to identify phase transitions in condensed liquid cesium metal by considering the variation of intermolecular potential parameters ɛ and r_m in the whole liquid range, with ɛ being the potential well-depth and r_m the position of minimum potential. These parameters were obtained from the parameters of a new equation of state that was derived recently by using the characteristic potential function. By this method, transitions at about 575, 800, 1000, 1350, and 1650 K were identified. Transitions at 575, 800, and 1000 K are weak but, the one at 1350 K is very significant and has been explored experimentally and theoretically as the metal non-metal transition (MNMT), which is a phase transition before the critical condition dominates the thermodynamics. Also variations of the linear correlation coefficient of the isotherms generate a spot point pattern of these transitions. Our observations at 575 K for ɛ and r_m are in accord with the anomalies in adiabatic thermal coefficient of pressure, density, viscosity, electrical conductivity, and structure factor.