bluuebunny/crossref_metadata_2025_split huggingface dataset:
Irreversible multilayer adsorption
Authors: Nielaba P. , Privman V. , Wang J.‐S. 
Published: July 2012

AbstractRandom sequential adsorption (RSA) models have been studied [1] due to their relevance to deposition processes on surfaces. The depositing particles are represented by hard‐core extended objects; they are not allowed to overlap. Numerical Monte Carlo studies and analytical considerations are reported for 1D and 2D models of multilayer adsorption processes. Deposition without screening is investigated; in certain models the density may actually increase away from the substrate. Analytical studies of the late stage coverage behavior show the crossover from exponential time dependence for the lattice case of the power law behavior in the continuum deposition. 2D lattice and continuum simulations rule out some “exact” conjectures for the jamming coverage. For the deposition of dimers on a 1D lattice with diffusional relaxation we find that the limiting coverage (100%) is approached according to the ∼1/√t power‐law preceded, for fast diffusion, by the mean‐field crossover regime with the intermediate ∼1/t behavior. In case of k‐mer deposition (k>3) with diffusion the void fraction decreases according to the power‐law t−1/2. In the case of RSA of lattice hard squares in 2D with diffusional relaxation the approach to the full coverage is ∼t−1/2. In case of RSA‐deposition with diffusion of two by two square objects on a 2D square lattice the coverage also approaches 1 according to the power law t−1/2, while on a finite periodic lattice the final state is a frozen random regular grid of domain walls connecting single site defects.
Critical phenomena at interfaces. Phase transitions at quantum surfaces
Authors: Leiderer P. 
Published: July 2012

AbstractThe quantum systems helium and hydrogen provide a versatile testing ground for studying interfacial phenomena. As examples, both some properties of surfaces near thermodynamic equilibrium, like layering and wetting, and nonequilibrium states of quench‐condensed disordered films are discussed. A further topic is the development of macroscopic instabilities of interfaces under external perturbation.
Surface amplitude ratios and nucleated wetting near a critical end point
Authors: Law Bruce M. 
Published: July 2012

AbstractWe examine two recently discovered phenomena which occur at the liquid/vapor surface of a critical binary liquid mixture; namely, (i) the universality of the critical adsorption amplitude ratio and (ii) the observation of the nucleation of wetting droplets after a temperature quench from the one phase into the two phase region.The recent theoretical work of Fisher and Upton on the universality of the surface tension amplitude ratio suggests that the ratio of the critical adsorption amplitude above and below Tc should also be universal. This is indeed found to be the case for five critical liquid mixtures where the modified critical adsorption amplitude ratio has an experimental value of RMA = 1.18±0.13. This result agrees reasonable well with the RG calculations of Diehl and Smock.In the two‐phase region, for sufficiently small reduced temperatures t, the critical liquid mixture hexadecane + acetone has an acetone‐rich wetting layer at the liquid/vapor surface at equilibrium. We examine the time development of this wetting layer after a temperature quench from the one phase into the two phase region. The liquid/vapor surface initially drops into a metastable surface state which is well described by critical adsorption. The lifetime,τ0, of this metastable state is many hours and depends upon the reduced temperature, t. At the nucleation time τ0 acetone‐rich droplets nucleate and grow at the liquid/vapor surface; good agreement is found for τ0 between theory and experiment for t≥8×10−5. An essential ingredient of the theory is the inclusion of a line tension term in the free energy of the nucleated droplet. At large times τ the droplets coalesce into a metastable wetting film which eventually undergoes a hydrodynamic instability to an equilibrium wetting film.
On the quantum finite‐size scaling
Authors: Korutcheva E. , Tonchev N. 
Published: July 2012

AbstractWe verify the finite‐size scaling hypothesis in the presence of quantum fluctuations up to one‐loop order in the ϵ‐expansion, using the formalism of Brézin [1], Brézin and Zinn‐Justin [2] and Rudnick et al. [3]. The analysis is performed within the framework of three models commonly used in the theory of structural phase transitions, superconducting phase transitions and Bose systems.
An orientational instability in the vapour and the liquid‐vapour interface of a dipolar hard sphere fluid
Authors: Kasch M. , Forstmann F. 
Published: July 2012

AbstractThe hard sphere dipole fluid shows an instability towards formation of oriented clusters in the vapour before condensation. The coexistence interface profile is derived from a WDA approximation of the direct correlation function. Integration of the equation for ∇ρ yields also the orientation of the dipoles near the interface.
Internal structure of microemulsions and sponge phases
Authors: Gompper G. , Goos J. , Kraus M. 
Published: July 2012

AbstractA simple Ginzburg‐Landau theory with a single, scalar order parameter is used to study the microscopic structure of microemulsions and sponge phases. Averages of the internal area and the Gaussian curvature have been calculated by Monte Carlo methods. The results are compared with results obtained from a variational approach in combination with the theory of Gaussian random fields and level surfaces. The results are found to be in reasonable qualitative agreement in the region of the phase diagram, where the microemulsion is stable. However, the variational approach fails to give a transition to the lamellar phase.
Surface‐ and interfacial tensions of liquid crystalline polymers
Authors: Runke Thomas , Song Bihai , Springer Jürgen 
Published: July 2012

AbstractSurface tensions (γA) of two side group liquid‐crystalline (lc) polymethacrylates and the interfacial tensions (γAB) between the lc‐polymers (LCP) and branched polyethylen respectively polymethylmethacrylat were measured in the isotropic and nematic phase with the pendant‐drop method. The surface tensions vs. temperature characteristics show anomalous behavior. The slope is initially negative but changes its sign near the isotropic‐nematic transition. This behavior is in agreement with surface‐tension measurements on low‐molar‐mass liquid crystals from other authors. The interfacial tension mainly depends on the density difference Δρ between the two phases, at the phase‐transition so we observed a jump of the interface‐tension values and a change of the slope. The pendant‐drop apparatus contains a video image processing system, that allows to acquire the pendant‐drop profile with a personal computer. The program used to analyse the experimental data is based on the “robust‐shape method”. This algorithm allows to calculate both the surface‐tensions and the interface‐tensions respectively with a personal computer.
Investigation of the reactions of the ethylchlorosilanes, tetraethylsilane and triethylsilanol with O(3P)
Authors: Buchta C. , Stucken D.‐V. , Vollmer J.‐T. , Wagner H. Gg. , Wittchow W. 
Published: July 2012

AbstractThe reactions of tetraethylsilane, triethylchlorosilane, diethyldichlorosilane, ethyltrichlorosilane and triethyl‐silanol with atomic oxygen in the ground state [O(3P)] have been measured in a discharge flow system with mass spectrometric detection. All measurements were performed in an excess of O‐atoms in the temperature range of 298 K<T <773 K. The following Arrhenius expressions for the bimolecular rate constants were obtained:magnified image
Hamilton‐jacobi dynamics for the solution of time dependent quantum problems I. Formalism and wave packet propagation in one dimension
Authors: Yurtsever Ersin , Brickmann Jürgen 
Published: July 2012

AbstractTwo methods for the numerical integration of the time‐dependent Schrödinger equation with given initial conditions (initial wave packet) are presented. The first method (method A) is based on the Schrödinger representation of the quantum‐dynamical system while the second one (method B) is based upon the intermediate representation. In both cases the quantum dynamical equation is transformed into a system of Hamilton‐Jacobi type equations of motion as occurring in multi particle classical dynamics, i.e. standard molecular dynamics techniques can be applied for the integration. The dynamics of a minimum uncertainty Gaussian wave packet in a strongly anharmonic oscillator is taken as an example.
Fluid structure around a rod‐like molecule and the additivity rule of the partial molar quantities. 1. A hard needle in a hard disk fluid
Authors: Yoshimura Y. 
Published: July 2012

AbstractFluid structure around a rod‐like molecule and its relation to the additivity rule of the partial molar quantities have been studied for a two‐dimensional system composed of hard disks of unit diameter and a hard needle of the thickness 0 (thin needle) or 1 (thick needle). The assumption that the additivity rule holds for the needle of arbitrary length (additivity rule in the strong sense (ARS)) gives the same equation of state for the hard disk fluid as the one derived from the scaled particle theory. The density expansion of the chemical potential shows that ARS does not strictly hold in the second order of density, and that the deviation from ARS is significant for the thin needle. The fluid structure around the needle at finite densities was studied by the Monte Carlo technique with the result that: (i) the fluid structure around the trunk part of the needle (trunk structure) is more distinct than the structure around the tip of the needle (end structure). (ii) The end structure shows little dependence on the needle length for a needle longer than 0.5, irrespective of the needle thickness. Especially, the distribution function along the extension line of the core of the needle is practically the same as the distribution function around the hard disk of the diameter equal to the thickness of the needle. (iii) Small oscillatory structure is developed in the trunk structure near the tip of the needle, which reflects the commensurate and incommensurate structure of solvent disks along the needle. ARS holds for the thick needle at each density studied within the statistical error, although ARS slightly underestimates the excess chemical potential of the thin needle. A useful expression for the packing efficiencies of the tip and the trunk part of the needle was derived using ARS for the thick needle.
Static light scattering experiments with non‐ionic surfactant/water mixtures of critical composition
Authors: Zielesny A. , Belkoura L. , Woermann D. 
Published: July 2012

AbstractResults of static light scattering experiments with C6E3/water and C8E4/water mixtures of critical composition carried out near the lower critical point of these systems are reported. If the critical temperature of the mixtures is constant in time (months) the critical exponent ν of the correlation length of local concentration fluctuations and that of the generalized susceptibility γ have values consistent with the values predicted theoretically for binary liquid mixtures (Landau‐Wilson‐Ginzburg model: ν = 0.63; γ = 1.24). The system specific critical amplitude ξ0 of the correlation length ξ has the values ξ0(C6E3/water) = 0.36 nm and ξ0(C8E4/water) = 0.54 nm. The evaluation of experiments with samples with time dependent critical temperatures introduces systematic errors. They lead to values of ν and γ smaller than the theoretically expected values. This observation could be one of the reasons for reports in the literature of non‐universal values of the critical exponents ν and γ in non‐ionic surfactant/water systems.
Guest‐host‐mixtures: A correlation between the dye's order parameter with thermodynamic and structural quantities
Authors: Hanemann T. , Haase W. 
Published: July 2012

AbstractA series of dyes containing a rigid aromatic core of the stilbene/azomethine type with approximate structural cylindrical symmetry as well as anthraquinone dyes with more spherical shape were investigated concerning their influence on thermodynamic properties of the liquid crystalline material CB5 (4'‐Pentyl‐4‐cyano‐biphenyl). Quantities like the transition temperatures, the biphasic range and the density discontinuity at the nematicisotropic transition were estimated via precise density measurements at different solute concentrations. The derived results like the slopes of the phase transition boundary lines and the resulting transition entropy were used to evaluate a semiempirical model which describes the change of the optical order parameter with the solute's mole fraction and the solute's structure. Experimentally the optical order parameter was estimated using the main transition in the visible range, which is parallel to the dye's long axis. The comparison of the experimentally obtained values with the data derived from our model is quite acceptable.
Phase diagram of the system water‐glycerol‐triton TX 100
Authors: Ranieri Giuseppe A. , Coppola Luigi , Terenzi Mario , Mesa Camillo La 
Published: July 2012

AbstractThe phase diagram of the system composed by water, glycerol and Triton TX 100, an industrial arylalkyl surfactant with polyoxyethylene glycol chain as polar head group, has been determined in a wide temperature range, to get information on the links between solvent effect and the formation of organized surfactant assemblies. The occurrence of solution and anisotropic phases is quite sensitive to the amount of glycerol, as well as to temperature.Experimental investigation on transport properties was made to get information on aggregate structure, as well as on micelle size and shape and on obstruction to solvent free diffusion.
Adsorption and hydrogenation of CO2 on precipitated iron catalysts: A combined TPD and Mößbauer study
Authors: Gieshoff J. , Buschmann H. W. , Vielstich W. 
Published: July 2012

AbstractThe hydrogenation of CO2 on a precipitated Fe‐catalyst and the formation of oxidic and carbidic iron phases were investigated. The hydrogenation reaction was studied by transient‐ and synthesis‐experiments, changes in the structure of the catalyst were followed by X‐ray‐diffraction and Mößbauer‐spectroscopy. In pure CO2 the iron is converted to magnetite. In CO2‐H2‐mixtures the catalyst is completely converted to cementite. In the initial state of this reaction small amounts of magnetite are formed in the pores of the catalyst. Methane is the main product of the hydrogenation.
Electronic properties of molten Cu‐CuTlTe2 and Ag‐AgTlTe2 systems
Authors: Uemura Osamu , Noguchi Takatoshi , Usuki Takeshi , Kameda Yasuo 
Published: July 2012

AbstractMeasurements of the electrical conductivity, magnetic susceptibility and thermoelectric power in liquid Cu‐CuTlTe2 and Ag‐AgTlTe2 systems have been carried out over wide temperature and composition ranges. These liquid systems exhibit the compound‐forming behavior in the vicinity of stoichiometric compositions, Cu3TlTe2 and Ag3TlTe2, such as the conductivity minimum, diamagnetic maximum and reverse in the sign of the thermoelectric power. Radial distribution analyses of the stoichiometric compositions, Cu3TlTe2 and Ag3TlTe2, by X‐ray and neutron diffractions indicate that the bonding nature of Cu‐Te and Ag‐Te in both alloys is rather covalent, differing from the ionic nature of Tl‐Te in liquid Tl2Te which is well‐known as a typical compound‐forming liquid.
Thermodynamics of liquid oxygen from molecular dynamics simulations
Authors: Lustig R. 
Published: July 2012

AbstractOxygen, modelled as a 2‐center Lennard‐Jones fluid, is studied along three isochores‐spanning the liquid region. Eleven different thermodynamic properties are obtained from simulations in the classical molecular dynamics ensemble. It is shown that most of them agree with experimental data within the combined uncertainty of experiment and simulation.
Determination of permeabilities through composite membranes by tracer diffusion experiments with 14C‐labeled Tartrazine®
Authors: Daniel T. , Seidel W. 
Published: July 2012

AbstractPermeabilities of tartrazine for different composite membranes were obtained by tracer diffusion experiments. 14C‐labeled tartrazine was synthesized from 14C‐aniline hemisulfate and tartaric acid. The composite membranes under investigation consisted of cellulose acetate or polyethersulfone supported by polypropylene membrane backings.
Micellar properties and structure of benzethonium chloride in isotropic aqueous solutions
Authors: Paradies H. Henrich , Thies Michael 
Published: July 2012

AbstractThe micellar structure of the cationic surfactant benzethonium chloride (BZC1) was analysed by small‐angle x‐ray scattering techniques. The shape, size and characteristics of the internal structure of BZC1 was studied by the contrast variation method at 20°C (CMC = 5.35 × 10−4Mol/l) by changing the electron density of the solvent through addition of polyols, e.g. sucrose or glycerol. The obtained scattering data were converted to absolute intensities, and analysed for intermicellar interference effects, by applying the rescaled mean spherical approximation method. The morphological parameters, micellar volume, average electron density, ϱ1, radius of gyration, Rν, second moment of the electron density distribution, “a”, and square average of the electron distribution, (Δϱ12), were determined from scattering data in the range of 0.001<h<0.08 Å−1. The apparent aggregation number (65 ± 10), degree of ionization (α = 0.15) were also determined by static light scattering. The micellar shape of BZCl was computed from Rv, and the maximum dimension of the micelle Dmax = 54.0 Å were obtained from the distance distribution function. The shape of the BZCl micelle is consistent with an oblate ellipsoid of revolution with a = 26.8 Å. The condensation effects of the chloride ions on the BZCl was compared for the “structural” model vs. the “effective model” from static light scattering and x‐ray scattering.The polydispersity in micellar size was found to be small, 1.55 in the weight‐average molecular weight and 17% in 〈V1〉. These values including (〈Mw,app〉), the one of the radius of gyration of the exclude volume (Rg = 20.3 ± 0.3 Å) are independent of the density of the solvent through addition of polyols.
Deuteron NMR relaxation, phase diagrams, and isotope effects in liquid mixtures of tetrahydrofuran/d2O/salt
Authors: Balevicius Vytautas , Weiden Norbert , Weiss Alarich 
Published: July 2012

AbstractNMR spin‐lattice relaxation timeT1and phase diagrams of deuterosubstituted tetrahydrofurans (THF‐hg, THF‐h4d4, THF‐d8) in D2O and D2O/salt (Salt = MeCl, Me = Na, K, Rb, Cs; CaCl2, AlCl3; MeOH, Me = Na, K) mixtures have been studied close to their lower critical solution points. It has been found that deuteration of THF leads to a shrinkage of the closed‐loop phase diagram THF‐h8‐xdx/D2O. It is an opposite and much stronger effect to the well‐known replacement of H2O by D2O in the system THF‐h8/H2O (D2O). The lower and the upper critical solution points (TC,L,TC,U) shift from 63.7 °C and 143.5 °C in THF‐h8/D2O to 84.5 °C and 128.5 °C in THF‐h4d4/D2O respectively, and they disappear in THF‐d8/D2O mixtures. This phenomena has been studied by precise (±0.01 °C) measurements of dependencies ofT1(2H) of THF and D2O deuterons on temperature. An increase of activation energies (Ea) of reorientational motion of THF‐d8has been found by introduction of ions into the solutions. The theoretical modeling of phase diagrams using renormalization‐group and decorated lattice methods shows that the observed changes ofTC,Lcan not be considered as a pure energetical effect where onlyEachanges due to additional interaction of polar molecules with the electric field of ions. The entropic contribution, viz. the appearance of additional orientations has to be taken into account as well.
Molecular dynamics simulation of pattern formation of two‐dimensional model membranes
Authors: Yurtsever Mine , Pamuk H. Önder , Brickmann Jürgen 
Published: July 2012

AbstractStructural changes in a two‐dimensional model membrane are studied with the aid of the molecular dynamics (MD) technique. The model parameters of the membrane forming molecules are that of a simplified phospholipid head group: each molecule consists of three spheres which represent choline, phosphate and the ester group. The head group molecule is treated as a rigid body. Their translational motion is constrained to two dimensions. The interaction of the molecules is modelled by Lennard‐Jones and Coulomb interactions. Time dependent configurations of a system with 120 molecules (with periodic boundary conditions) are analyzed by visual inspection of trajectory plots and by the study of radial distribution functions and local order parameters. The ensemble of model particles is studied as a function of the interaction parameters and the temperature.For high temperatures the system shows liquid type behaviour. For moderate and low temperatures the formation of patterns is observed. There are definitely two trends of ordering. For strong dipole‐dipole interaction (relative to the dispersion attraction) of the model particles the individual molecules form ordered chains with decreasing temperature. However, this trend is not monotonous. For T = 400 K the local order parameter has a maximum as a function of temperature which is interpreted as an interference between dipole‐dipole ordering and an ordering principle which is related to the molecular shape.A different order phenomenon occurs when the dispersive attraction of the molecular force centers is increased while the dipole‐dipole interaction is kept constant. For relatively larger dispersion attraction the dipoles are orientally trapped by this ordering principle leading to the breakdown of dipole order.Although the present model approach cannot be overinterpreted with respect to real biomembranes, it may be very useful for the systematic studies on the interaction of bulky molecules with membranes and the study of the influence of external parameters (like pressure) on structure building.
Density functional theory: Modelling of surface tensions for molecular fluids
Authors: Winkelmann J. , Brodrecht U. , Kreft I. 
Published: July 2012

AbstractBoth density profiles, surface tension and the corresponding phase equilibria are governed by the same intermolecular forces. Thus an appropriate theoretical model should be able to describe both interfacial and bulk properties by the same interaction potential. The Local Density Approximation to the Density Functional Theory is applied to the modelling of surface tension and saturated liquid densities of nonpolar molecular fluids. To take into account the nonspherical molecular shape a site‐site Lennard‐Jones interaction potential is used. The reference system is described by a hard convex body equation of state whereas the attractive contributions to the free energy were obtained from a mean‐field approximation. For a series of diatomics structures (O2, N2, CO, Cl2, ethane, ethylene) and convex core geometries (n‐alkanes, benzene, CCl4) potential parameters were estimated using surface tensions and liquid densities. The geometrical parameters for the n‐alkanes could be extrapolated up to n‐octane. A functional dependence of the potential parameters on the chain length and geometry of the molecule is discussed.