bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature Measurements in High Pressure Combustion
Authors: Stricker W. , Woyde M. , Lückerath R. , Bergmann V.
Published: July 2012

We report on a fundamental study of N2 and H2 CARS thermometry in a high‐pressure, premixed methane/air flame. Based on CARS spectra of high quality, models were developed for spectral shape calculations in order to determine accurate temperatures. Rotational Raman spectra were used to measure an independent reference temperature. The limits of applicability were shown. Single‐pulse N2 CARS thermometry on a subscale ramjet combustor with 3 bar pressure inside the combustion chamber was performed.
Temperature Measurement by UV‐Degenerate Four Wave Mixing
Authors: Ewart P.
Published: July 2012

The derivation of temperatures of gas phase media from spectra generated by DFWM, induced by frequency scanned narrow linewidth lasers, is briefly reviewed. The technique of multiplex or broadband DFWM is described, by which spectra, and hence temperatures, may be obtained by a single shot of a novel broadband “modeless” laser. Experimental measurements of broadband DFWM lineshapes from OH are briefly described and compared with theoretical predictions. Results of temperature measurements in premixed methane/air flames using broadband DFWM spectra are reported. Systematic errors arising from the effect of absorption are discussed, improvements to and applications of the technique to turbulent media are briefly considered.
Detection of Polyatomic Molecules using Infrared Degenerate Four‐Wave Mixing
Authors: Germann G. J. , Mcilroy A. , Dreier T. , Farrow R. L. , Rakestraw D. J.
Published: July 2012

Degenerate four‐wave mixing detection of methane and acetylene is demonstrated using rotational‐vibrational transitions for resonance enhancement. High resolution spectra (<0.007 cm−1) of methane and acetylene, near 3000 and 3300 cm−1 respectively, have been acquired using a single‐longitudinal‐mode optical parametric oscillator. These experiments suggest that infrared degenerate four‐wave mixing provides a new diagnostic capability for the sensitive detection of polyatomic molecules with high temporal and spatial resolution.
Application of Laser‐Induced Fluorescence and CARS for Combustion Diagnostics
Authors: Aldén M. , Bengtsson P.‐E. , Georgiev N. , Löfström C. , Martinsson L. , Neij H.
Published: July 2012

Laser diagnostic techniques have during the last decade been successfully applied for diagnostics of combustion processes. The main advantages with these techniques are that they are inherently non‐intrusive and that spatially as well as temporally resolved information can be achieved. The current paper will exemplify two different laser spectroscopic techniques: Laser‐Induced Fluorescence (LIF), and Coherent anti‐Stokes Raman Scattering (CARS), which are currently the most used laser techniques for temperature and species concentration measurements in combustion systems.
2D‐Diagnostics in Industrial Devices
Authors: Arnold A. , Bräumer A. , Buschmann A. , Decker M. , Dinkelacker F. , Heitzmann T. , Orth A. , Schäfer M. , Sick V. , Wolfrum J.
Published: July 2012

The high spectral brightness of tunable high power excimer lasers allows the two‐ and three‐dimensional application of techniques like laser‐induced fluorescence (LIF), Mie and Rayleigh scattering for industrial applications. The construction of these lasers allows easy transportation and installation to perform measurements at combustion facilities which can not be moved. In combination with suitable filters and gated image‐intensified CCD cameras techniques are now available to measure multi‐dimensional distributions of temperatures and concentrations. Simultaneous measurements of temperature fields and hydroxyl radical distributions were performed to study the influence of turbulence on large premixed natural gas flames. A combination of temperature and nitric oxide concentration measurements yielded information about the correlations between NO formation and burner design in domestic gas burners. LIF and Mie scattering of fuel and hydroxyl radicals were used for measurements in IC engine simulators, Otto and Diesel engines.
Laser Surface Processing and Diagnostics
Authors: Preuß S. , Stuke M.
Published: July 2012

Laser processing has become a powerful tool for surface modification and is applied successfully in many areas. In this article we focus on laser ablation as a very attractive way of surface patterning. We report both applications and mechanistic studies. In the first part of this paper we describe a two‐step method for the patterning of technical polymer surfaces by laser ablation. With this process, micron or even submicron structures can be obtained in a simple way. By doping polymers with photochromic compounds the feasibility of this process is improved drastically. In the second part we report the ablation of lithium niobate (LiNbO3), polyimide (PI), poly(tetrafluoroethylene) (PTFE, teflon) and poly(methylmethacrylate) (PMMA) by 0.5 ps UV excimer laser pulses at 248 nm. Time‐resolved measurements were carried out with pulse pairs of variable delay in the range — 200 ps to +200 ps. The ablation rate is very sensitive to the time delay between the two pulses and contains information about the dynamics of the process. For LiNbO3, efficient shielding is observed within a few picoseconds. For polyimide, excited state absorption is found to decrease the ablation rate for delay times below 30 ps. For PTFE and PMMA, and the total fluence just above threshold, the ablation rate versus time delay shows an autocorrelation type behavior with a full width at half maximum below 400 fs, since two‐photon absorption dominates the ablation process. A simple ablation model based on the assumption, that the absorbed volumetric energy density has to exceed a certain threshold value, will be presented. It describes the observed ablation rates for PTFE precisely.
Time Resolved Trace Analysis of Exhaust Gas by Means of Laser Mass Spectrometry
Authors: Weickhardt C. , Boesl U.
Published: July 2012

The large number of components and their very different and rapidly varying concentrations complicates the analysis of exhaust gases of combustion engines. Here, a new analytical technique, based on the combination of resonance enhanced multiphoton ionization, performed by pulsed tunable lasers, and time of flight mass spectrometry is presented. It allows the simultaneous detection of several trace components with concentrations ranging from 1 ppm up to several percent with a quantitative accuracy better than 10%. Time resolution of 10 ms could be achieved with this system. A preliminary list of substances detectable by this technique contains 25 substances; some of them belong to the strongest compounds inducing ozone formation.
A Bundle of Tapered Fibers Transmits 830 mJ/Pulse of 308 nm XeCl Laser Pulses
Authors: Devel A. , Pfleiderer C. , Wolfrum J. , Greulich K. O.
Published: July 2012

Improvements of a tapered bundle of 32 tapered fibers permit the transmission of XeCl‐excimer laser pulses (308 nm) with high energy densities. More than 2000 laser pulses of 530 mJ/pulse output at the bundle's end could be transmitted without fiber damage achieving a transmission of approx. 40% using a Siemens XP 2020 XeCl excimer laser. With a SOPRA VEL XeCl excimer laser a peak output energy of 830 mJ/pulse at the bundle's end was possible. Measurements of the beam profile of the bundle were also performed. The beam profile of the near field was very inhomogeneous with an average energy density of 2250 mJ/cm2. Due to the high divergence of the radiation at the end of each fiber, the beam profile of the bundle's far field was better homogenized. An average energy density of 550 mJ/cm2 was achieved. For applications as surface treatments it is necessary to observe the surface to be objected to laser treatment on‐line during radiation. A simultaneous quality‐control integrated in the bundle is possible by means of difference reflectometry.
Collisional Narrowing and Spectral Shift in CARS Spectra of Molecular Nitrogen and Oxygen at Pressures up to 2500 bar and Temperatures of 850 K
Authors: Dreier T. , Ridder M. , Schiff G. , Suvernev A.
Published: July 2012

Vibrational‐rotational CARS spectra of molecular nitrogen and oxygen at high densities and temperatures are recorded using a scanning CARS‐spectrometer. Measurements are performed at pressures up to 2500 bar and temperatures up to 850 K. The spectral line position and halfwidth of the fully collapsed Q‐branch are determined for pure N2, O2, N2/O2 mixtures and Ar/O2 mixtures. Comparisons of the experimental data with different theoretical models for the rotational energy transfer are also presented. Three quantum mechanical approaches (MEG‐, ECS‐, PEG‐laws) are compared with a classical description of the relaxation process treating the angular momentum as a continuous variable.
Design of Multiplex Dyes
Authors: Sauer Markus , Schulz Andreas , Seeger Stefan , Wolfrum Jürgen , Arden‐Jacob Jutta , Deltau Gerhard , Drexhage Karl H.
Published: July 2012

Fluorescent dyes which are almost identical in their absorption and emission spectral characteristics but differ in fluorescence lifetime (“Multiplex Dyes”) have been developed for analytical applications. First investigations to design such dyes were carried out with rhodamines. In order to influence the excited state lifetime without changing the spectral characteristics we studied rhodamines modified with non‐conjugated substituents that promote non‐radiative transitions. We used two different methods to control the fluorescence lifetime in rhodamine dyes with rigidized amino groups: (A) Substitution with benzyl derivatives of different electron acceptor strength at the amino position. (B) Substitution of the carboxyphenyl group by phenyl groups with reduced steric requirements and varying acceptor properties.
Two‐Dimensional Imaging of OH Radicals in Spark Ignition Kernels by Laser Induced Fluorescence
Authors: Xu J. , Warnatz J.
Published: July 2012

Two‐dimensional laser‐induced fluorescence imaging of OH radicals has been used to observe the temporal and spatial development of the OH distribution during the ignition of a lean methane‐air mixture (ϕ = 0.56) ignited by an electrical spark. A frequency‐doubled dye laser, which is pumped by a XeCl excimer laser, has been used to excite fluorescence from OH radicals. A series of OH concentration maps from a cross‐section through the ignition kernel during the ignition process have been obtained. It can be seen that the gas flow induced by the initial shock wave from the breakdown phases has a significant influence on the development of the ignition kernel. The ignition kernel is produced by a narrow cylindrical plasma channel with high temperature, then expands to an ellipsoid during the ignition. At about 1 ms after the onset of the spark the ignition kernel expands from the ellipsoid to a toroidal shape. A flame front emerges from the ignition kernel at about 10 ms.
Dielectric spectroscopy on CiEj/water mixtures as a function of composition
Authors: Kaatze U. , Gabriel B. , Pottel R.
Published: July 2012

At 25°C the complex dielectric permittivity of mixtures of water with low‐weight poly (ethylene glycol) monoalkyl ethers (CiEj) has been measured as a function of frequency v (1 MHz ≤ v ≤ 55 GHz) and mole fraction x(0 ≤ x ≤ 1). Various relaxation spectral functions are fitted to the measured spectra. It is found that the dielectric relaxation of all liquids (i, j = 2,2; 4,2; 6,2; 4,3; 4,1) can be consistently described by a sum of a Debye term with discrete relaxation time and a Davidson‐Cole term with an underlying unsymmetrical relaxation time distribution. With the exception of the C4E3/H2O mixtures the Debye term vanishes at high content of CiEj molecules (x > 0.25). It is assumed that this term represents a water‐rich subphase while the Davidson‐Cole term reflects a microphase of low water content. With the C4H3/H2O system crankshaft‐like motions of the C4E3 molecule obviously also contribute to the Debye term which exists also in the spectrum of the pure organic liquid. The parameters of all spectra are discussed with respect to the composition of the microphase of low water content, to effects of dipole orientation correlation, and to the mechanism of dielectric relaxation in associated liquids.
Electronic spectra of 7,14‐dithioketo‐5,7,12,14‐tetrahydroquinolino‐[2,3‐b]‐acridine in solution and in the solid state
Authors: Mizuguchi Jin , Rochat Alain Claude , Rihs Grety
Published: July 2012

7,14‐Dithioketo‐5,7,12,14‐tetrahydroquinolino‐[2,3‐b]‐acridine (DTQ) is a thionated derivative of quinacridone (QA) that is known as a red pigment. Thionation of QA brings about an intense near‐IR absorption in the solid state which is of practical importance for GaAsAl‐laser printers and optical information storage systems. The electronic properties of DTQ have been investigated in solution and in the solid state in order to characterize the near‐IR absorption from the standpoint of intermolecular hydrogen bonding. The electronic state of the DTQ‐chromophore is found to be most sensitively affected by an environment of proton acceptors which interact with the NH group of the chromophore. In solution, the hydrogen bonds between the NH group and the O atom of a solvent cause a bathochromic shift by 5 – 15 nm relative to the absorption spectrum in dioxane. This is interpreted as being due to electron transfer from the proton to the nitrogen atom, thereby increasing the electron density in the chromophore. A similar increase in electron density is also operative in the solid state through the intermolecular hydrogen bonds between the NH group of one DTQ and the S atom of the neighboring molecule. This is mainly responsible for the bathochromic displacement of DTQ in going from solution to the solid state. The near‐IR absorption is, however, not explicable in terms of the hydrogen bonding interaction alone. Another intermolecular interaction, such as π‐π interactions along the stacking axis, appears to be operative that might lead to a near‐IR absorption.
Hydrogen bonding effect on the electronic spectra in complexes of 1,4‐dithioketo‐3,6‐diphenyl‐pyrrolo‐[3,4‐c]‐pyrrole with n‐methyl‐2‐pyrrolidone and dimethylsulfoxide
Authors: Mizuguchi Jin
Published: July 2012

1,4‐Dithioketo‐3,6‐diphenyl‐pyrrolo‐[3,4‐c]‐pyrrole (DTPP) is known as the material suitable for laser printers and optical information storage systems using GaAsAl‐diode lasers. Hydrogen‐bonded complexes of DTPP with N‐methyl‐2‐pyrrolidone (NMP) and Dimethylsulfoxide (DMSO) have been grown from solution as single crystals: DTPP/(NMP)2 and DTPP/(DMSO)2. In both complexes, one DTPP molecule is bonded to two solvent molecules through the hydrogen bonds between the NH group of DTPP and the O atom of the solvent. The hydrogen bonding effect on the electronic spectra has been investigated in these complexes on the basis of the PPP, CNDO/S and INDO/S calculations. The hydrogen bonding in solution and in complexes displaces the longest‐wavelength π ‐ π * visible absorption band towards longer wavelengths. This is interpreted as being due to CT type interaction of hydrogen bonding which involves a partial electron transfer from the oxygen atom to the NH bond. The longest‐wavelength absorption bands in both complexes are polarized along the hydrogen bonding axis, and this agrees with the direction of the transition moment predicted from the calculations. On the other hand, a prominent reflection band appears in DTPP/(DMSO)2 for the polarization perpendicular to the hydrogen bonding axis. This is assigned to an intermolecular CT transition along the stacking columns composed of alternating DTPP and DMSO molecules.
Kinetics and mechanism of the formation of an iron(III) complex with Nα‐pyridoxyl‐L‐tryptophan
Authors: Ozawa Tomohiro , Jitsukawa Koichiro , Einaga Hisahiko
Published: July 2012

The formation of an iron(III) complex with a new multidentate ligand, Nα‐pyridoxyl‐L‐tryptophan(1, H2pltp), has been investigated thermodynamically and kinetically in an aqueous 0.10 mol dm−3 sodium perchlorate solution at 25°C. A 1:2(metal : ligand) complex of 1 forms with much higher stability constant (logβ12/mol−2 dm6 = 38.29±0.28) than the related complex, bis(pyridoxylidene‐L‐tryptophan)iron(III), having the azomethine group (log β12/mol−2 dm6 = 18.38±0.10 [3]). This effect was explained by the contribution of amino nitrogen of higher basicity to the thermodynamic stability. The complex formation reaction proceeds through two parallel pathways of Fe3+ +H3pltp+ and FeOH2+ +H4pltp2+ and also another pathway of FeOH2+ +H3pltp+ with slower coordination of the first ligand to iron(III). The mechanistic rate‐determining step for the formation of the complex was the coordination of the phenolato oxygen to a central metal atom, followed by the rapid donations of the amino nitrogen and carboxylato oxygen atoms.
Structure and morphology of gas phase deposited ice
Authors: Langel W. , Fleger H.‐W. , Knözinger E.
Published: July 2012

Amorphous ice was prepared by deposition of H2O vapour diluted in heat exchange gases such as He or Ar at low temperatures (13 to 45 K). This technique is faster than the deposition of pure H2O vapour. The rapid sticking of condensing molecules on the cold solid leads to a poor short range order inside the grains. The high nucleation rate during vapour deposition results in small grain sizes and microporosity. Structure and morphology of the resulting amorphous ice samples were characterized by x‐ray diffraction. The radial distribution function was calculated from the diffraction data of pure ice and proved to be consistent with the Continuous Random Network model. Diffraction patterns of krypton layers on the amorphous ice reflect the morphology of the substrate: at the beginning micropores with a diameter of 15–20 Å and a volume of 0.045 cm3/g are filled. At higher mass coverages outer grain surfaces and large voids are covered by krypton.
The protonation constants of glycine in NaCl at 25 °C based on the pitzer and scatchard models data analysis by ridge regression
Authors: Fiol S. , Brandariz I. , Herrero R. , Vilariño T. , de Vicente M. Sastre
Published: July 2012

We have potentiometrically determined the protonation constants of glycine in NaCl solutions of variable ionic strength. The data thus obtained have been analysed by using the interaction models of Scatchard and Pitzer. The presence of multicollinearity among the explanatory variables of the model has been evidenced through the coefficients of the correlation matrix and the variance inflation factor (VIF). We have applied the ridge regression (RR) to address the problem arising' from multicollinearity and the results are critically compared with those obtained by ordinary least squares regression (OLS).
Zero kinetic energy (ZEKE) photoelectron spectrum and coincident mass spectra of methyl formate
Authors: Waterstradt Eckhard , Jung Rolf , Belling Thomas , Müller‐Dethlefs Klaus
Published: July 2012

The ZEKE photoelectron spectrum of methyl formate in a supersonic jet was recorded using multibunch VUV synchrotron radiation. The adiabatic ionisation potential is determined to 87 390 cm−1 (10.835 eV). Three yet unobserved normal modes of the electronic ground state (ν10, ν11, and ν12) and the progression of a mode previously assigned to ν4 are observed. Ab initio calculations reveal a large Duschinsky rotation upon ionisation of three modes implying that the ν4 progression corresponds to an OCO‐antisymmetrical stretch motion. The finer vibrational structure observed on the electronic ground state above 1500 cm−1 is considerably perturbed due to the anharmonicity of the potential surface.
How does a transition zone affect the electric field enhanced water dissociation in bipolar membranes?
Authors: Mafé Salvador , Ramirez Patricio , Manzanares José A.
Published: July 2012

The changes in the electric field in the space charge regions and the corresponding effect on the water dissociation rate when a transition zone exists between the layers of a bipolar membrane are theoretically studied. A quasi‐equilibrium approach based on the Poisson‐Boltzmann equation for the space charge interfacial regions is used. The transition zone acts to decrease significantly the water dissociation rate. However, for realistic values of the thickness δ of the transition zone and provided that the ohmic drop over δ be small, this decrease in the dissociation rate is not very dependent on δ. The results obtained give theoretical support to some recent experimental findings.
Surface phase transitions of solids. Influence of a surface on order‐disorder transformations in binary alloys
Authors: Peisl J.
Published: July 2012

A report is given on a study of the order parameter and the order parameter fluctuations at the Fe3Al (110) surface when it approaches the order‐disorder phase transformation. X‐ray scattering under grazing incidence and exit was employed and gave the necessary surface sensitivity. The temperature dependence of the critical surface scattering at and around the (111) superstructure reflection was investigated. The critical behaviour is strongly influenced by the surface. The new surface exponents have been determined and are β1 = 0.75±0.06, γ‖ = –0.33±0.06, η‖ = 1.52±0.04 and ν = 0.60±0.15. The surface dominated phase transition belongs to the ordinary transition class. Scaling laws can be verified.
Surface melting: A density functional approach
Authors: Löwen H. , Ohnesorge R. , Wagner H.
Published: July 2012

A microscopic theory of surface melting is described and applied to Lennard‐Jones systems. Our approach is based on density functional theory with the hard sphere fluid as a reference system. In particular we use a weighted density approximation which yields an accurate Lennard‐Jones bulk phase diagram. Within a practically free minimization of the functional, we find surface melting of a Lennard‐Jones crystal for different surface orientations. Furthermore the hard‐sphere crystal‐fluid interface and the hard‐sphere crystal at a hard wall are explored with density functional theory. It is found that the crystal‐fluid surface tension of hard spheres is extremely small and that the hard wall prefers to be covered by a hard‐sphere‐solid at solid‐liquid coexistence.
Surface diffusion: An STM view
Authors: Frenken J. W. M. , Kuipers L. , Hoogeman M. S.
Published: July 2012

We employ a high‐speed high‐temperature scanning tunneling microscope to investigate two manifestations of surface diffusion. The step fluctuations observed on metal surfaces are shown to be the result of the fast diffusive motion of pre‐existing kinks in the steps. We find that a high density of kinks can be induced by a minute concentration of impurities. At sufficiently high temperatures, surfaces can “jump” to physical contact with the tip of the microscope. Such jumps are followed by a “sintering” process in which a massive connecting neck rapidly builds up between the surface and the tip.
Structural and dynamical properties of surfaces and the effect of premelting
Authors: Schommers W.
Published: July 2012

The effect of premelting is of particular interest in connection with the theory of melting. In this paper, we discuss structural and dynamical properties of surfaces of semi‐infinite crystals as well as of nano‐clusters, which show the effect of premelting. The investigations are based on molecular dynamics calculations: Different models are used for the systematic study of the effect of premelting. In particular, the behaviour of the following functions have been studied: pair correlation function, generalized phonon density of states, and the mean‐square displacement as a function of time. The calculations have been done for krypton since for this substance a reliable interaction potential is available.
A temperature dependent LEED study of the Si(111) surface
Authors: Göbel H. , Mayer C. , Setzer C. , Kling B. , von Blanckenhagen P. , Schommers W.
Published: July 2012

The Si(111) surface shows spontaneous (7×7) reconstruction at low temperatures. At about 1130 K deconstruction to a (1×1) structure takes place. We have studied the reconstructed surface and the quenched, unreconstructed surface by low energy electron diffraction (LEED) as a function of temperature. A kinematical LEED data analysis has been performed in order to be able to discriminate between different structure models.
Phase transitions of two‐dimensional surface compounds at multicomponent alloy surfaces
Authors: Uebing Christian
Published: July 2012

In general the chemical composition of multicomponent alloy surfaces exhibit significant deviations from the bulk composition due to thermally activated segregation processes. Upon cosegregation epitaxially stabilized two‐dimensional surface compounds are formed on substrate surfaces with suitable orientation, e.g. CrN on Fe‐15%Cr‐N (100), CrC on Fe‐15%Cr‐C (100) and VC on Fe‐3%V‐C (100) and Fe‐3%Si‐0.04%V‐C (100). As indicated by sputter depth profiles the thicknesses of such surface compounds correspond to a monolayer.

In some of these systems the temperature dependence of surface coverage displays phase transition behavior. On Fe‐3%Si‐0.04%V‐C (100) the VC surface compound is formed at temperatures up to 635 °C. Sharply above that temperature the VC surface compound vanishes. Simultaneously the onset of Si segregation is observed leading to a c(2×2) structure at saturation. Such behavior could be attributed to a temperature‐driven first order phase transition between VC surface compound and c(2×2) Si. A different type of surface phase transitions is observed on Fe‐15%Cr‐N (100). At temperatures T>600°C the two‐dimensional surface compound CrN is epitaxially stabilized on the alloy surface. Upon lowering the temperature the nucleation of three‐dimensional CrN surface precipitates is initiated according to the bulk phase diagram of the Fe‐Cr‐N system. Further growth of such CrN surface precipitates leads to thick CrN films on the substrate surface.

Finally Monte Carlo simulations utilizing a lattice gas model of two interpenetrating square sublattices are presented, each sublattice may accommodate one type of adsorbed or segregated species M or X. It is shown that this model is well suited to describe surface compound formation and associated phase transitions.
Structure of the effective hamiltonian for liquid‐vapor interfaces
Authors: Napiórkowski M.
Published: July 2012

A nonlocal and non‐Gaussian expression for the effective Hamiltonian of a fluctuating liquid‐vapor interface is derived from the density functional theory for inhomogeneous simple fluids. After applying a gradient expansion one obtains as the leading term the standard capillary‐wave Hamiltonian. The next to leading terms are proportional to the Gaussian curvature and to the mean curvature squared. Microscopic expressions for the coefficients in this expansion are derived. The breakdown of the gradient expansion for long‐range interparticle forces is pointed out; this break‐down is also reflected in the nonanalytical behavior of the (microscopically derived) wave‐vector‐dependent surface tension. The connection between recent scattering experiments and the derived Hamiltonian is discussed.
On the stiffness of an interface near a wall
Authors: Fisher Michael E. , Jin Albert J. , Parry Andrew O.
Published: July 2012

The relevance of the bare stiffness, (l), of an interface at distance l from a planar wall, for the renormalization‐group theory of critical‐wetting instabilities in short‐range, (d = 3)‐dimensional systems is briefly recalled. A careful derivation is presented of an expression for (l) at the van der Waals/mean field level in terms of the order‐parameter profile m∏(z, l) of a planar interface. The analysis completes and improves the treatment of Jin and Fisher [Phys. Rev. B 47, 7365 (1993)].
Gravity, confinement, and phase equilibria
Authors: Indekeu J. O. , Rogiers J.
Published: July 2012

We study a fluid or Ising lattice gas confined between two horizontal walls with separation L, in a gravitational field of strength g. For identical walls (with equal surface fields h1 = hL) the familiar capillary condensation and capillary criticality extend to non‐zero g. Finite‐size scaling predicts that the locus of criticality shrinks to g = 0 for L→∞, in the manner g α L−(βδ/ν+1). For opposing walls (with h1 = –hL) we confirm that bulk two‐phase coexistence is suppressed, for g = 0, to below the wetting temperature Tw. However, for small g (and h1 of appropriate sign) bulk two‐phase coexistence extends to higher temperatures that increase extremely rapidly with g, up to a maximum temperature that is shifted from the L = ∞ bulk critical point in the manner Tc,max(L)–Tc(∞)αL−1/ν, conform with finite‐size scaling.
Diffuse scattering of X‐rays and neutrons from surfaces and interfaces
Authors: Haase A. , Dietrich S.
Published: July 2012

Based on a modified first Born‐approximation we derive a general expression for the kinematic cross‐section of x‐rays and neutrons impinging on an arbitrary interfacial structure. The scattering intensity is expressed in terms of the two‐point correlation function of the atomic number densities. Our approach takes into account the exact expression for the refraction of the penetrating waves at the mean interface profile, for example the multiple reflection occurring in a multilayer system, the evanescent waves under the condition of total reflection, or the distortion of the incoming plane wave due to the refraction at a smooth interface. Therefore our results allow a sophisticated analysis of the scattering data in order to extract the lateral correlations from the diffuse scattering intensity. To illustrate this formalism we discuss applications for particularly interesting systems such as liquid‐vapor interfaces, wetting films, and multilayers.
Wetting of heterogeneous substrates
Authors: Napiórkowski M. , Koch W. , Dietrich S.
Published: July 2012

On the basis of a microscopic density functional theory we investigate the structure of van der Waals fluids exposed to the long‐range potentials of spatially and chemically inhomogeneous substrates. As a paradigm of a spatial inhomogeneity we consider a wedge‐shaped substrate. The mean position of the interface between the liquidlike adsorbed film and the bulk vapor phase displays van der Waals tails. Our results differ from those obtained by a phenomenological approach which, under certain approximations, can be derived from the nonlinear integral equation for the interfacial profile. The numerical solution allows us to predict a scaling behavior for the excess coverage as function of the asymptotic film thickness. The chemical inhomogeneity under consideration consists of a flat substrate with two different species each occupying a quarter space. The asymptotic values of the finite film thicknesses are attained according to van der Waals tails. In both systems the formation of adsorbed films is determined by the line contribution to the free energy. For the patched substrate the diverging thickness of the liquid layer is associated with a logarithmic divergence of the line tension.
Divergence of the point tension at wetting
Authors: Abraham D. B. , Latrémolière F. , Upton P. J.
Published: July 2012

The line tension, (free energy associated with the line of contact) is expected to have interesting singular behaviour at the wetting transition, as has already been inferred from mean field theory and scaling arguments. In order to investigate this behaviour, we consider an exactly soluble two‐dimensional Ising model with appropriate wetting boundary conditions and investigate suitable definitions of , now a point tension, associated with the junction of an interface tilted with average angle θc and another lying along the substrate. Size‐dependent fluctuations in the point of contact indicate that be defined through a convolution sum. Hence ≈ ln (1/θc) as θc ↓ 0 (wetting transition), which can be understood as a consequence of the entropic repulsion of the tilted part of the interface against the substrate. This logarithmic divergence is consistent with the recent scaling hypothesis of Indekeu and Robledo.
Wetting dynamics. On the decay of metastable states near a first‐order wetting transition
Authors: Bausch R. , Blossey R.
Published: July 2012

For a system with a first‐order wetting transition we discuss the decay of metastable wetting layers by nucleation. The assumption of detailed balance implies that some essential properties of the decay process follow from statics alone. E.g., the lifetime of the metastable states is predominantly determined by the excess free energy of critical nuclei. The latter are either droplets on a microscopic layer or dents in a macroscopic layer on the wall of the system. We discuss the form and the excess free energy of the critical nuclei in various regions of the phase diagram.
Liquid/liquid interfacial instability in the vicinity of the critical point of a binary liquid mixture
Authors: Wolf H. , Woermann D.
Published: July 2012

The system 2‐butoxyethanol/water is used to study the dynamics of the instability of the liquid/liquid interface in the vicinity of the lower critical point of the system. The values of the viscosity parameter A and the interfacial parameter B which determine the shape of the interfacial instability are changed by varying temperature at which the experiments are carried out. The change of the shape of the interfacial region is monitored using a CCD‐video‐camera. The pictures of the liquid/liquid interface are analysed by determining the number of “viscous fingers”, the width of the mixing zone and the length of the liquid/liquid contour length as function of time. The analysis of the data is based on the work of Tryggvason and Aref (J. Fluid. Mech. 136, 1–30 (1983); 154, 287 (1985)).
Irreversible multilayer adsorption
Authors: Nielaba P. , Privman V. , Wang J.‐S.
Published: July 2012

Random 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

The 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

We 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.
Finite size dependence of the helicity modulus within the mean spherical model
Authors: Danchev Daniel
Published: July 2012

The finite‐size behavior of the helicity modulus is analyzed within the three‐dimensional mean spherical model. In contrast to previous heuristical predictions, for the helicity modulus in the finite‐size critical region there are no “resonant” logarithmic corrections.
On the quantum finite‐size scaling
Authors: Korutcheva E. , Tonchev N.
Published: July 2012

We 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

The 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

A 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

Surface 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

The 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:

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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

Two 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

Fluid 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

Results 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

A 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

The 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.