bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic Relaxation under Fast Internal Rotation in Liquid Part II). A Variable Temperature NMR Study Using 13C Spin‐Lattice Relaxation Time Measurements in Liquid Mesitylene
Authors: Suchanski W.
Published: July 2012

The 13C nuclear spin‐lattice relaxation times of ring and methyl carbons in liquid mesitylene (1,3,5‐trimethyl‐benzene, 1,3,5‐TMB) have been measured as a function of temperature. The results have been analyzed in terms of two relaxation mechanisms: intramolecular dipole‐dipole coupling and spin‐rotation interaction. In order to separate these contributions, also the nuclear Overhauser enhancement factors have been studied. The results have been analyzed in terms of the theory of Gordon and Langevin models for internal motion of methyl groups with a low barrier to internal rotation and are in good agreement with predictions of both theories.
Computer Simulation of Chiral Liquid Crystal Phases II. The Use of Twisted Boundary Conditions
Authors: Memmer R. , Kuball H.‐G. , Schönhofer A.
Published: July 2012

Using the Monte Carlo technique, we study an ensemble of N = 256 particles interacting via a chiral modified Gay‐Berne potential introduced in part I. We introduce twisted boundary conditions which allow the formation of helical phases with lower potential energy and a larger pitch in comparison with the results of simulations using cubic periodic boundary conditions. The amount of chiral and achiral energy contributions to the total potential energy are discussed for the obtained cholesteric, helical smectic and blue phases.
Dielectric Studies on Liquid Crystals under High Pressure: V. Static Permittivity and Low Frequency Relaxation Process in 4‐n‐Heptyl‐4'‐Cyanobiphenyl (7CB)
Authors: Brückert T. , Würflinger A. , Urban S.
Published: July 2012

Dielectric studies have been performed on 4‐n‐heptyl‐4'‐cyanobiphenyl, 7CB, between 305 and 341 K and at elevated pressures up to 150MPa. From measurements of the dielectric relaxation (up to 13 MHz) we calculate the activation enthalpy (decreasing with increasing pressure) and the activation volume (decreasing with increasing temperature) in the nematic state. The low‐frequency process connected with molecular rotations about the short molecular axis was analysed in terms of the Martin‐Meier‐Saupe theory, yielding q ≈︁ 5 kJ/mol for the nematic potential. The dielectric behaviour is similar to previous results for 5CB and 6CB.
Liquid Crystals in Information Technology
Authors: Schadt Martin
Published: July 2012

To establish and to improve the increasingly complex interaction between man and machine requires sophisticated, versatile and compact displays. The liquid crystal display (LCD)‐technology is the only technology which is capable to display equally well the simple time information of digital wrist watches as well as the complex color images of future high definition television sets; it is a key technology in the years to come.

There have been three major prerequisites for the establishment and the success of the LCD technology since the early 1970s. Namely, the discovery of potent electro‐optical field effects on which LCDs are based, the successful search for liquid crystal (LC) materials with effect‐specific properties, and last but not least, the development of the technological tools required for manufacturing LCDs.

Virtually all of today's commercial LCDs are based on the twisted nematic (TN)‐ or on various supertwisted nematic (STN)‐effects. Those LC‐material properties and electro‐optical effects that essentially determine the operability of LCDs are reviewed. The performance of TN‐LCDs, STN‐LCDs and optical mode interference (OMI)‐LCDs in modern, high information content applications is shown. Included are recent developments such as TV compatible, time multiplexed OMI‐LCDs and operation of TN‐LCDs in bright LCD‐color projectors whose functional parts, such as polarizers, optical filters and modulators consist entirely of liquid crystal devices. Moreover, it is shown that planar, uniaxial alignment of liquid crystals cannot only be achieved by conventional, mechanically treated substrates, but also by a novel, photo‐induced alignment concept. Photo‐induced alignment opens up the possibility to realize azimuthal variations of the liquid crystal director on LCD‐substrates and the possibility to achieve high resolution director pattern. Thus, among many other possibilities, LCD‐stereo projection, in‐situ interference filters for STN‐LCDs and new optical storage applications become feasible.
The β‐Relaxation in Ferroelectric Liquid Crystals
Authors: Schönfeld A. , Kremer F.
Published: July 2012

Broadband dielectric measurements (102 Hz to 109 Hz) on ferroelectric liquid crystals (FLC) beeing oriented in the bookshelf geometry were performed. In the frequency regime between 106 Hz and 109 Hz one dielectric relaxation process — the β‐relaxation — is observed and it is shown — for the first time — that this process has a DC‐bias field dependence similar to the (low frequency) Goldstone‐mode. The β‐relaxation is assigned to the hindered rotation (libration) of the mesogene around its long molecular axis. It has an Arrhenius‐type temperature dependence. A critical behaviour at the phase transition SA/S (nonferroelectric/ferroelectric) is not observable. These experimental findings lead to a modified picture for the molecular origin of ferroelectricity in FLC.
Electrooptical Properties of Liquid‐Crystalline Rigid Rod‐Like Polymers with NLO‐Active Sidegroups
Authors: Winkelhahn H.‐J. , Servay Th. K. , Kalvoda L. , Schulze M. , Neher D. , Wegner G.
Published: July 2012

The second order nonlinear susceptibility χ(2) of a novel class of poled polymer films was investigated by means of the attenuated total reflection (ATR) method. The polymers are composed of an aromatic polyester backbone to which NLO active stilbene chromophores and flexible alkyl side chains are alternately attached. The optical properties and the dynamics of relaxation of the poled state were strongly depending on the length of the aliphatic side chains. The relaxation determined at different temperatures above and below Tg showed a temperature dependence that differs from an Arrhenius type behaviour. An empirical equation which relates the temperature dependence of the relaxation times to the glass transition temperature is presented.

The polyester main chains could be macroscopically aligned in strong magnetic fields. Electric poling of the samples with aligned main chains results in ratios of χ χ which deviate significantly from the ratio of 3 one obtains for samples with isotropically distributed main chains. This behaviour is explained by the solid state structure of this kind of polymer, which is best described by a sequence of alternating layers of polyester backbones and flexible side chains.
Collective Motions and Viscoelastic Properties in Main Chain Liquid Crystal Polymers. A Deuteron Spin Relaxation Study
Authors: Heaton N. , Reimer D. , Kothe G.
Published: July 2012

Multipulse dynamic NMR techniques have been employed to investigate collective motions and viscoelastic properties in a main chain liquid crystal polymer and low molar mass analogues in the nematic phase. Transverse deuteron spin relaxation times measured as a function of pulse spacing using a modified Carr‐Purcell‐Meiboom‐Gill pulse sequence are analysed in terms of a simple hydrodynamic model for nematic director fluctuations. Combining these results with those of NMR slow sample spinning experiments allows determination of the effective viscosity and the average elastic constant of the material. Results are compared for compounds with different molecular weights and with the results of analogous proton field‐cycling experiments. The viscosity is found to increase approximately as the square of the molecular weight, Mn, whilst the elastic constant shows a much shallower Mn dependence apparently tending to a plateau value at moderate molecular weights.
Flüssigkristalle mit fluorhaltigen Alkylgruppen
Authors: Bartmann Ekkehard
Published: July 2012

A series of compounds with the basic structures typical for liquid crystals (cyclohexyl benzenes, biphenyles, bicyclohexylbenzenes and cyclohexylbiphenyls) and alkyl groups containing fluorine (methyl to pentyl, mono‐ to perfluorinated, attached to the benzene end of the core) was investigated. Their physical properties relevant for application in LC displays such as phase ranges, dielectric anisotropies and viscosities are discussed as functions of the structural parameters of the fluorinated alkyl chains such as chain length, content of fluorine and position of the fluorine atoms in the chain.
Characterization of Mesoscopic Structures from Polymerizable Amphiphiles: The Water‐SSPOM System
Authors: Von Berlepsch H. , Strey R.
Published: July 2012

Solutions of sodiumsulfopropyloctadecylmaleate (SSPOM) and water form ordered lamellar structures. Remarkable is that the structures form below the Krafft discontinuity indicating a frozen state of the hydrocarbon chains. Phase behaviour and microstructure were characterized using optical microscopy, differential scanning calorimetry (DSC), electrical conductivity, backscattering of light, small‐angle X‐ray scattering (SAXS) and freeze fracture electron microscopy (FFEM). We find a highly swollen lamellar structure displaying iridescent colours when illuminated with white light. The repeat distance of the bilayer membranes is estimated by light and X‐ray scattering and shows a non‐linear dependence on inverse surfactant concentration. Above the chain melting temperature near 37°C the liquid crystalline hexagonal phase (Ha) is observed.
Local Monitoring of Absolute NO2 Concentrations in Ambient Air by Multipass Absorption Spectroscopy
Authors: Armerding W. , Walter J. , Rüger Chr. , Spiekermann M. , Comes F. J.
Published: July 2012

A method for monitoring tropospheric NO2 is described which makes use of differential absorption spectroscopy in the red at 600–620 nm. The absorption path‐length of up to 2.7 km is folded inside a 6 m White cell type multiple reflection system. The detectable fractional absorbance of 1 × 10−5 corresponds to a sensitivity of 50 pptv and 200 pptv NO2 for measurements performed at 612.7 nm or 616.0 nm, respectively. The averaging time is at maximum one minute. Since the system can be operated simultaneously in the VIS and the UV (second harmonic) it is capable to measure NO2 as well as OH, SO2, CH2O and C10H8 at the same time. The MOAS (Multipass Optical Absorption Spectroscopy) instrument is interesting for in situ measurements of atmospheric NO2 with high spatial and temporal resolution and sensitivity. It can be used as an external standard to calibrate other NO2 devices under field conditions. Its capability to measure OH and NO2 simultaneously within the same compartment offers a unique possibility to perform field tests of model calculations of fast tropospheric photochemistry.
Solid State NMR Relaxation and Hindered Rotations in Fully Asymmetric Local Environments
Authors: Knop E. , Latanowicz L. , Reynhardt E. C.
Published: July 2012

The temperature dependences of spin‐lattice relaxation rates in the laboratory and rotating frames and the second moment of an NMR line with I = 1/2 have been determined for molecular motions in fully asymmetric triple and double potential wells. With a view to emphasising some of the important features of the results, a number of examples are given.
In‐Situ Gas Analysis with Infrared Lasers
Authors: Ebert V. , Hemberger R. , Meienburg W. , Wolfrum J.
Published: July 2012

In the first part of the paper we present the experimental validation of models describing the NOx removal from flue gases through the SNCR process. The Selective Non‐Catalytic NOx Reduction process was realized in a high temperature flow reactor. A lead salt diode laser system combined with second derivative spectroscopy monitored the concentration of NO, NH3, N2O, NO2, HCN behind the reactor. After the injection of ethane at concentrations of up to 1000 ppm the shift (up to 220 K) of the temperature window of the SNCR process was measured.

In the second part a Laser In‐Situ Ammonia‐monitor (LISA) based on a 13CO2‐wave guide laser is used to establish an on‐line control of the SNCR in an industrial environment by measuring in‐situ the excess ammonia behind the reduction zone. With differential absorption spectroscopy and a special referencing scheme sensitivities in the order of several ppm·m of NH3 at atmospheric pressure have been achieved even in heavily dust laden flue gases. With a multi‐channel LISA system the 2‐dimensional NH3 distribution in the flue gas channel of an experimental coal burner system could be measured and the persistence of spatial inhomogeneities, caused by incomplete mixing of NH3 and the flue gas could be shown.

In the third part we present first results aimed at the measurement of the local O2‐concentration in combustion systems. With a thermally stabilized 5 mW NIR diode laser at 760 nm we detected oxygen at atmospheric pressure with a sensitivity of less than 500 ppm·m using two beam absorption spectroscopy.
PLIF Imaging of Fuel Fraction in Practical Devices and LII Imaging of Soot
Authors: Tait Nigel P. , Greenhalgh Douglas A.
Published: July 2012

In this paper we discuss the development and application of 2D imaging methods for the study of fuel‐air mixing and the in‐situ measurement of soot in flames. Fuel imaging is based on planar laser‐induced fluorescence (PLIF) with pulsed UV lasers. Fuel concentrations may be estimated from the fluorescence of common fuel components or through the addition of a fluorescent species or seed. PLIF of fuel is shown to be applicable to both premixed and non‐premixed combustion. The choice of fluorescent seed and the role of interfering species, such as combustion derived polyaromatic hydrocarbons (PAH) and laser‐induced incandescence from soot, are discussed. The application of the method is illustrated with an example of an isothermal mixing study in a gas turbine combustor sector rig and measurements in a simple flame. The results demonstrate that PLIF can achieve high spatial resolution, circa 0.4 mm, in a combustor with dimensions of order of 400 mm. The dynamic range of the measured intensities exceeds 1500 with typical signal‐to‐noise ratios of better than 100:1. A major source of interference in PLIF studies of non‐premixed flames is laser‐induced incandescence (LII) from soot particles. We discuss the role of LII both as an interference in PLIF imaging and as an imaging method for soot volume fraction. A detailed analysis of the physics of LII is presented on a theoretical model developed. Results from the model and supporting experimental data are presented. LII images from a highly turbulent sooting flame indicate that soot structures, probably in the form of thin sheets as small as 100 μm across, are formed through vortex mixing.
Analysis at Surfaces and Interfaces. Second Harmonic Generation (SHG) and Sum Frequency Generation (SFG) Diagnostics of Diamond Surface Chemistry
Authors: Chuang T. J.
Published: July 2012

Nonlinear second harmonic generation (SHG) and sum frequency generation (SFG) laser spectroscopies have been applied along with conventional surface analytical techniques to study the gaseous interactions on diamond surfaces. Recent results relevant to diamond CVD processes are discussed.
Laser Excitation of Surface Phonons and Wave Pulses
Authors: Hess Peter
Published: July 2012

Excitation of surface phonons or surface acoustic wave (SAW) pulses with a broad frequency spectrum up to 200–300 MHz using focused laser pulses is discussed. Several optical and piezoelectric methods for broadband detection of the resulting surface displacements are considered. It is shown that for an anisotropic single crystal the SAW velocity can be measured with an accuracy of 0.1% as a function of the crystal plane and direction due to the short wave pulses achieved. In a layered system strong dispersion occurs, since the waves with different wavelengths probe different depths corresponding to their wavelength and thus travel with different velocities in the heterogeneous solid. From a non‐linear dispersion effect several film properties can be obtained, such as thickness, density and elastic constants (e.g. Young's modulus and Poisson's ratio). Results are presented for fullerite and diamondlike carbon films. The characteristics of the pulsed laser method are compared with Brillouin scattering, interdigital transducers and the acoustic microscope.
Photodynamics on Surfaces Revealed by Laser Studies
Authors: Hasselbrink E.
Published: July 2012

Fundamental mechanisms for photochemistry at metal and semiconductor surfaces are discussed. Experiments probing these mechanism are presented discussed for molecular oxygen adsorbed on palladium(111). Isotope effects in photodesorption and photodissociation are shown to provide insights into the excitation transfer mechanisms and the probability of nonquenching events.
Joint PDFs of Scalar Quantities in Turbulent Diffusion Flames by Raman and Rayleigh Scattering
Authors: Hassel F. , Hundhausen A. , Klos Th. , Sprenzel U. , Bockhorn H.
Published: July 2012

Simultaneous time and space resolved measurements of CO2, O2, CO, N2, H2O mole fractions and temperature are performed by using Raman and Rayleigh scattering. The investigated system is a turbulent jet of CO injected into the coflowing hot exhaust of a lean CH4/N2/O2‐flame. Mean values, joint one‐point 6D‐pdfs and characteristic statistic quantities are determined. The results for mean values agree well with measurements from independent methods. Determined joint one‐point pdfs resemble more‐dimensional normal distributions. The pdfs are non‐symmetric in the reaction zone with positive or negative correlation coefficients for the reactants. This indicates that the low Damköhler number system under investigation is not diffusion controlled. A quantification for this is given by the calculation of correlation coefficients and turbulence intensities. The measurements are suitable to verify models for transport equations of pdfs in turbulent reacting flows at low Damköhler numbers.
Measurements of OH by LIF and Temperatures by Holographic Interferometry in Catalytically Stabilized Combustion of Hydrogen: Comparison of Measurements and Numerical Simulation
Authors: Buser S. , Benz P. , Schlegel A. , Bockhorn H.
Published: July 2012

To investigate the catalytically stabilized combustion of hydrogen in a duct, hydroxyl radical and temperature distributions have been measured by LIF and holographic interferometry, resp. A detailed two‐dimensional numerical model has been developed. For the heterogeneous reaction mechanism simplifications are introduced which are justified by an analysis of the elementary heterogeneous reaction mechanism proposed by Hellsing et al. 1991. Experimental results and numerical simulation are in good agreement. The numerical model allows the identification of the relevant coupling mechanism between heterogeneous and homogeneous combustion of hydrogen. These are: radical recombination reactions at the wall, diffusive fluxes of H2, O2, H2O due to the heterogeneous reactions and heat transfer from the wall to the gas. The desorption of radicals from the surface into the gas does not play a significant role in this system.
Time‐Resolved Fluorescence Studies of Labelled Nucleosides
Authors: Han K.‐T. , Sauer M. , Schulz A. , Seeger S. , Wolfrum J.
Published: July 2012

Synthesis, steady‐state and time‐resolved fluorescence measurements of carboxycoumari labelled aminonucleosides (thymidine, cytidine, guanosine) are described. The data indicate a strong influence of the coupling position, the linker length and the structure of the coumarin dye on the quenching rates.
Preferential solvation of some copper (II) salts in dioxane‐dimethylsulphoxide (DMSO) mixtures
Authors: Sreekumar T. K. , Kalidas C.
Published: July 2012

The solvation behaviour of some copper(II) salts viz. copper(II) iodate, copper (II) benzoate and tetraDMSOcopper(II) perchlorate has been investigated by Gibbs transfer energy and solvent transport number measurements. The Gibbs transfer energies of the salts have been split into their ionic components by employing the nLJP method. The transfer energies of the copper (II) ions decrease continuously with the addition of DMSO while those of the anions increase under the same conditions. The solvent transport number, Δ, of DMSO is positive and passes through a maximum for all salts around XDMSO = 0.35 to 0.45. The results indicate a heteroselective solvation of the salts, the copper (II) ion being selectively solvated by DMSO and the anions by dioxane.
Static relative permittivity of sulfur hexafluoride up to 30 MPa
Authors: Kita T. , Uosaki Y. , Moriyoshi T.
Published: July 2012

The static relative permittivity ϵr of sulfur hexafluoride, SF6, has been measured along ten isotherms from 273.15 to 353.15 K at pressures up to 30 MPa. The experimental ϵr‐values obtained were accurate to within ±0.02 per cent, except for some values in the vicinity of the critical point. The critical relative permittivity ϵr,c was estimated to be 1.281 ±0.001 by application of the rectilinear diameter law. The ϵr‐values were combined with densities obtained from the equation of state in the literature to calculate the molar polarization Pm given by the Clausius‐Mossotti equation. The results of ϵr and Pm as a function of fluid density are discussed; the volume polarizability α' of SF6 was evaluated to be 6.67×10−30m3 and 6.59×10−30m3 using the values of the first dielectric virial coefficient Aϵ determined by two methods. Further, the values of α' for carbon dioxide and nitrous oxide were recalculated to be 2.94×10−30 m3 and 3.20×10−30m3, respectively, from Aϵ‐values obtained by the newly employed method.
A neural network hamiltonian governing the formation of RNA base‐pairing patterns
Authors: Fernández Ariel , Belinky Alejandro
Published: July 2012

We implement a neural network associating a two‐state unit to each pair of bases in a fixed RNA sequence. The connectivity matrix is constructed following the cooperativity rules of nucleation for RNA hairpin formation and base‐pair stacking. Attractive neural patterns correspond to stable RNA secondary structures. Moreover, the Gibbs probability of a pattern coincides with the Boltzmann weight of the corresponding structure.
Staining of biomembranes with amphiphilic hemicyanine dyes
Authors: Fromherz P. , Röcker C.
Published: July 2012

The binding of amphiphilic dyes to biomembranes is described as a distribution equilibrium between a three‐dimensional and a two‐dimensional phase. Ostwald‐type coefficients and formal binding constants are measured for lipid vesicles and hemicyanine dyes with different hydrophilic‐hydrophobic balance. The staining of neuron membranes is discussed as a basis for optical recording of membrane voltage by hemicyanine dyes.
The induced infrared spectrum of H2 Adsorbed on NaCl film at 8 K. Rotation of ortho‐H2 in the state J = 1 on the surface
Authors: Heidberg J. , Dierkes W. , Schönekäs O. , Schwarte R.
Published: July 2012

The induced fundamental infrared spectrum of H2 adsorbed on NaCl film at 8 K has been observed under ultrahigh vacuum conditions. There are two adsorption sites. For each site a splitting of the vibrational fundamental into a doublet is resolved. The doublet is assigned to para‐H2 and ortho‐H2 by its close resemblance to the doublet Q1 (0) and Q1(1) calculated and observed in gaseous and matrix‐isolated H2. According to Ben Ephraim and Folman the lowest adsorption potential corresponds to a H2 orientation parallel to the surface and slightly perturbed free rotation about an axis normal to the surface. However, because of space quantization, the ortho‐H2 molecules are tilted up in the rotational state J = 1 and perform a hindered rotation about an axis tilted to the surface.
Vibrational relaxation of HCl(v = 1) in HCl/CO/Ar gaseous mixtures between 296 and 173 K
Authors: Losert O. F. J. , Schramm B.
Published: July 2012

Vibrational relaxation of HCl(v = 1) in HCl/CO/Ar gaseous mixtures has been measured between room temperature and 173 K by the laser‐induced fluorescence (LIF) technique. Rate constants for the total relaxation and the V‐V relaxation have been determined showing that the relaxation is governed by the V‐V process. For the rates of the V‐R,T processes which relax HCl(v = 1) and CO(v = 1) upper limits are given. As in similar systems relaxation efficiency is higher at lower temperatures.
Elementary reactions of NH (a1Δ) and NH(X3Σ) with N, O and NO
Authors: Hack W. , Wagner H. Gg. , Zasypkin A.
Published: July 2012

The elementary reactions of NH(a1Δ) with N, O, and NO and the reactions of NH(X3Σ−) with N, O and NO were studied in a quasi static laser flash photolysis cell at room temperature (T=298T) and low pressures (15≤p/mbar≤20). NH(a) was produced by HN3 laser photolysis at λ = 248 nm. NH(X) was obtained from the fast quenching of NH(a) with Xe. The O atom source was the NO + N reaction ([N]0>>[NO]0), with N atoms formed in a microwave discharge of N2/He. NH(a), NO(X) and the primary products NH(X), OH(X) and NO (X) were detected by pulsed laser induced fluorescence (LIF). The absolute N atom concentrations were determined via the reaction of N with NO. Time resolution was achieved by time delay between photolysis and probe laser pulses.

For overall depletion:

magnified image

the following rate constants were obtained: k1, = (6.0±1.5)·1011 cm3/(mol·s); k2 = (5.6±2)·1012cm3/(mol·s); and k3 = (1.8±0.2)·1013 cm3(mol·s).

By fitting the NH(X) concentration profiles, determined experimentally, with computer simulations, the following rate constants for quenching channels were obtained: k1q = (6.0±1.2)·1011 cm3/(mol·s) and k2q = (1.2±0.3)·1012cm3/(mol·s). For the reaction pathways of reaction (2):

magnified image
Viscosity of two non‐ionic amphiphile/water mixtures of critical composition: Study of the systems triethyleneglycolmonohexylether (C6E3)/water and tetraethyleneglycolmonooctylether (C8E4)/water
Authors: Zielesny A. , Limberg S. , Woermann D.
Published: July 2012

The shear viscosity of a C6E3/water and a C8E4/water mixture of critical composition (lower critical point) is measured in a wide temperature range (C6E3/water: 2 mK≤(Tc‐T)≤43.913 K; C8E4/water: 5 mK≤(Tc‐T)≤ 39.517 K) using capillary viscometry. The viscosity η is dominated by singular contributions in a narrow temperature range only (C6E3/water: (Tc‐T)≤0.8K; C8E4/water: (Tc‐T)≤0.2K). This temperature range is much smaller than that found in “simple” binary mixtures of low molar mass components. The temperature dependence of η of the system C6E3/water at temperatures away from Tc, in the crossover regime and in the critical regime close to Tc is analyzed successfully by the same methods developed for the analysis of viscosity data of binary mixtures of low molar mass components. The method fails in the analysis of the viscosity data of the system C8E4/water. This is probably caused by the temperature‐dependent influence of micelles on the viscosity.
Diffusion Coefficients in aqueous solutions of magnesium nitrate at 298 K
Authors: Lobo Victor M. M. , Ribeiro Ana Cristina F. , Verissimo Luis M. P.
Published: July 2012

Differential diffusion coefficients of magnesium nitrate in water, at 298 K and at different concentrations, have been measured using a conductimetric cell. The results are discussed on the basis of the Onsager‐Fuoss and Pikal theories. The cell uses an open‐ended capillary method and a conductimetric technique is used to follow the diffusion process by measuring the resistance of a solution inside the capillaries at recorded times.
The electrochemical quartz‐microbalance in media of changing viscoelastic properties, and the design and characterization of a suitable driver electronics
Authors: Soares D. M. , Kautek W. , Fruböse C. , Doblhofer K.
Published: July 2012

In this work we develop a new description of the behaviour of the electrochemical quartz‐microbalance (EQMB). It takes into account the phase shift introduced by the driver and also the influence of changing visco‐elastic properties of the medium in contact with the quartz (i.e. film and/or liquid).

Based on these concepts a new driver circuit has been designed. Its electronics is advanced relative to the classical drivers in two points: a) It allows a partial impedance analysis of the quartz, b) it introduces a controllable phase shift into the system driver+crystal. Thus, an evaluation and even correction of the obtained frequency‐results becomes possible.

Experimental frequency data obtained in liquids with different visco‐elastic properties were corrected with the new approach and compared with theory.

The capability of determining the resistive component of the quartz' impedance was also used to determine the limits of the rigid‐layer approximation for polypyrrole‐films.
Electrochemical reduction of anthracenes on poly(vinylferrocenium) coated Pt electrodes in acetonitrile
Authors: Gülce Handan , Özyörük Haluk , Yildiz* Attila
Published: July 2012

The electroreduction behaviour of anthracene and some of its derivatives on poly(vinylferrocenium) coated Pt electrodes was investigated and compared with that on uncoated Pt surface using' cyclic voltammetry in acetonitrile/0.1 M TBAP solutions. The changes occurring in the structure of the film after the electrode reactions were followed by IR spectroscopy and DSC measurements. Catalytic reduction of the anthracene derivatives occur when electrode reactions were carried out on the coated surface.
Phase transitions at Al and Au surfaces: Deconstruction, roughening and premelting
Authors: von Blanckenhagen P.
Published: July 2012

A short outline of structural phase transitions at surfaces and their experimental verification will be given as an introduction, which will be followed by a review of experimental and theoretical results for Al and Au surfaces.

We have studied Au(111)‐, Au(110)‐ and Au(100)‐surfaces by medium energy ion scattering (MEIS) experiments and Au(110)‐ as well as Al(110)‐surfaces by low energy electron diffraction (LEED) experiments.

At the Au(110) (2×1)‐surface deconstruction is accompanied by the disappearance of monoatomic steps. At about 40 K above the deconstruction temperature roughening sets in. The rough surface begins to smoothen if due to the increasing diffusion the outermost layers start to transform into a quasi‐liquid state. The growth of the quasi‐liquid layer with increasing temperature follows a logarithmic law. Preroughening, roughening and premelting transitions have been detected at the Al(110)‐surface. Open questions regarding these phase transitions will be discussed.
X‐ray studies of the thickness and roughness of thin adsorbed fluid layers
Authors: Pershan P. S.
Published: July 2012

This paper is a brief summary of a talk delivered at the “Discussion Meeting on Phase Transitions at Interfaces”, Bad Herrenalb, Germany in September 1993 on the application of synchrotron X‐ray scattering to the study of liquid surfaces. More complete discussion of much of this material can be found in the publications cited in the manuscript. The oral presentation was concerned with the application of X‐ray specular reflectivity to study structure of the liquid/vapor interface for various liquids, including superfluid4He, liquid gallium and thin liquid wetting layers of classical liquids adsorbed on solid surfaces. The effects that correlations between the height fluctuations on the top and bottom surfaces of thin adsorbed liquids have on the reflectivity and diffuse scattering from thin films will be discussed.
Interfacial segregation and wetting transition in fluid binary metallic mixtures
Authors: Müller S. C. , Tostmann H. , Nattland D. , Freyland W.
Published: July 2012

First indications of wetting transitions in alkalimetal‐alkalihalide solutions have been obtained in previous optical studies. In order to study this transition continuously as a function of temperature and composition along the coexisting curve and in the homogeneous phase we have started SHG‐measurements on these systems at the fluid‐sapphire interface. First results of this experiment in comparison with the ellipsometric results will be presented. On the other hand, in order to exclude influences of the substrate on the interfacial behaviour we have investigated the liquid‐vapour interface in the liquid alloy Ga‐Bi (metallic system with miscibility gap) by spectroscopic ellipsometry. The main interest concentrates on possible discontinuous changes of the optical constants at the interface with varying composition and temperature. First results are presented.
Experimental observation of prewetting in a binary liquid mixture
Authors: Bonn Daniel , Kellay Hamid , Meunier Jacques
Published: July 2012

We present experimental evidence for the existence of a prewetting transition for the binary liquid mixture of cyclohexane and methanol. For certain compositions in the mixed region of the phase diagram, a first‐order thin to thick film transition can be observed. The observed transition exhibits a large hysteresis. It is shown that the prewetting line approaches the coexistence curve tangentially. Also, the prewetting critical point displays 2‐D Ising‐like criticality. These findings are compared to recent experiments on other systems, in which prewetting was also observed.
Interfacial wetting in binary liquid mixtures
Authors: Getta X. , Dietrich S.
Published: July 2012

We classify the wetting behavior of binary liquid mixtures at their liquid‐vapor interface. The criteria with respect to the atomic interactions between the two species are whether the Hamaker constant of that interface fulfills either the sufficient conditions for the absence of a wetting transition, or the necessary conditions for critical wetting, or the necessary conditions either for being wet already at low temperatures of for undergoing a first‐order wetting transition upon approaching the critical end point along the triple line. Based on the Percus‐Yevick theory we scan the whole parameter space which determines the structure of the bulk phase diagrams. In addition we compare the predictions of the Percus‐Yevick theory for the bulk phase diagrams and the number densities of the fluid bulk phases with experimental and simulation data as well as with different theoretical approaches.
Wetting of laterally structured surfaces
Authors: Müller‐Buschbaum P. , Tolan M. , Press W. , Brinkop F. , Kotthaus J. P.
Published: July 2012

An x‐ray scattering study of a laterally structured solid surface wetted by a liquid is reported. GaAs (001) samples with etched trapezoidal surface gratings are used as substrates. Due to the lattice spacing of d = 5900 Å and the height h of about 450 Å such gratings can be regarded as a row of free edges and wedges. The special wetting behaviour of these wedges with a liquid film of CCl4 was studied using x‐ray reflectivity in the region of total external reflection. The reflectivity of the film on top of the laterally structured GaAs substrate is explained by model calculations which contain the electron density depth profile perpendicular to the surface. The thickness of the liquid wetting film on top of the stepped surface was obtained from the fit of the data.
Dynamic wetting on porous and non porous substrates. Influence of surface tension, viscosity and porosity
Authors: André V. , Zosel A.
Published: July 2012

In this work, we have studied the wetting behaviour of liquids on closed and non closed surfaces. Contact angle measurements were performed on polymer and glass surfaces (non porous, closed surfaces) and on calibrated glass filters (porous, non‐closed substrates). Silicone oils (polydimethylsiloxane) having different viscosities η1 (between 1 and 1000 Pas) and a low surface tension (γ1 = 21 mN/m) were used as well as liquids with a higher surface tension (solutions of polyisobutylene in decaline; γ1 = 31 mN/m and Polyacrylic Acid in water; γ1 = 66.3 mN/m) also covering a large range of viscosities.

The contact angle measurements were done in the dynamic mode with the help of an image processing system and a CCD Camera. The modification of the contact angle could be recorded with a frequency of one picture per 66 ms. For the closed surfaces (polymer and glass), the volume of the deposited drop remains constant whereas it changes with time in case of a porous system. The image processor allows the acquisition of the contact angle (θ), of the drop volume (V/V0) and of the drop radius (r/R0), where V0 is the volume and R0 the radius of the original drop.

The curves of cos θ and r/R0 vs time for the liquids can be superimposed in a master curve by plotting versus γ1·t/η1·R0 (also called reduced time). For the non porous substrates (glass, Polyethylenterephthalat, Polytetrafluoroethylen), the master curves coincide at small wetting times which means that the early stage of the wetting process is determined only by the properties of the wetting liquid. The influence of the surface tension was not clearly observed but the viscosity plays an important role at the beginning of the wetting process.

The porous substrates (glass filters) were proved to have a different behaviour. The master curves could be obtained for cos θ vs reduced time and V/V0 vs reduced time for different porosity grade (15–40 μm compared to 40–100 μm) for the polyisobutylene solutions as well as for the silicon oils (polydimethylsiloxane). However there is no agreement between polydimethylsiloxane and polyacrylic acid since for comparable viscosities the master curve for PAA is being shifted by a factor of about 1000 to longer times. Thus, contrary to the closed surfaces, the surface tension seems to be a limiting factor for the liquid penetration rate.
Growth kinetics of Kr and Xe multilayers physisorbed on graphite
Authors: Mannebach H. , Knorr K.
Published: July 2012

Multilayers of Kr and Xe physisorbed on graphite have been evaporated by intense laser pulses and the readsorption transients have been followed in time with an ellipsometer. The transients are discussed in reference to the equilibrium adsorption isotherms.
Instabilities at driven contact lines
Authors: Brenner Michael
Published: July 2012

A physical explanation of the mechanism for the fingering instability at driven contact lines is presented. Semi‐quantitative predictions for the growth of the fingers as a function of time, the most unstable wavelength, and the initial growth rate are deduced. These predictions are compared with recent experiments.
A grand isostress ensemble monte carlo study of thin films under shear
Authors: Schoen Martin , Diestler Dennis J. , Cushman John H.
Published: July 2012

Thin films of monatomic fluid constrained between two plane‐parallel structured solid walls have been simulated by Monte Carlo under conditions (fixed temperature, chemical potential and normal stress or load) prevailing in high‐precision measurements of surface forces. Several phases of the film (corresponding to different numbers of layers of fluid parallel with the walls) are generally consistent with these conditions, but only one is thermodynamically stable; the others are metastable. When the walls are properly aligned, epitaxial solidlike phases are stable. These melt under shear, eventually becoming metastable, whereupon a drainage (or imbibition) transition occurs, leading to a stable phase with fewer (or more) layers.
Hydrodynamics of a membrane bound to a substrate
Authors: Seifert Udo
Published: July 2012

We briefly review recent theoretical work on the dynamical equilibrium shape fluctuations of a membrane interacting with a substrate. Solving the hydrodynamical equations we determine the damping rate γ(q) as a function of the wave‐vector q. For small q, we find universally γ∼q2. In an intermediate q‐range, the damping rate behaves like either γ∼q6 (monotonic damping) or γ∼q2 (non‐monotonic damping) depending on the relative sizes of the mean separation and the parallel correlation length, which are both determined by the adhesion potential. For large q, one recovers the behavior γ∼q3 of a free membrane. A numerical solution of the dispersion relation is presented for a membrane subject to electrostatic repulsion in a linear attractive potential.
Complex fluids. Weakly to strongly structured mixtures
Authors: Kahlweit M.
Published: July 2012

This paper addresses the transition from weakly to strongly structured liquid mixtures of water, alkanes (Bk), and nonionic amphiphiles (CiEj). Starting with weak short‐chain amphiphiles, it is shown that the three‐phase bodies in such mixtures evolve from tricritical points (tcp) upon increasing either the carbon number k of Bk at fixed amphiphilicity (i,j) of CiEj, or upon increasing (i,j) at fixed k. In the first case, the three‐phase bodies grow monotonically with increasing distance from the tcp, whereas in the second case, they first grow, pass through a maximum in the range of medium‐chain amphiphiles, and shrink again as one proceeds to long‐chain amphiphiles. In that range in which the three‐phase bodies pass their maximum, one observes the gradual evolution of properties that distinguish weakly from strongly structured mixtures, such as the evolution of cmc surfaces, non‐wetting of the water/oil interface by the amphiphile‐rich middle phase, an o/w → w/o dispersion inversion near the mean temperature of the three‐phase body, and a correlation peak in the I(q) curves of SANS. This permits drawing a rather well defined border line between weakly and strongly structured mixtures in (i,j)–k space.
Bulk and interfacial properties of polar fluids
Authors: Frodl P. , Groh B. , Dietrich S.
Published: July 2012

Based on a suitable density functional theory for inhomogeneous fluids we investigate both the bulk phase diagram and interfacial structures of polar fluids in general and of Stockmayer fluids in particular. We derive a scheme which allows us to analyze one‐component fluids composed of molecules with strong permanent dipole moments which are shown to affect significantly the bulk phase diagram. The results for the bulk phase diagram are in good agreement with published Monte Carlo data. Furthermore we investigate the profiles of the number density and of the orientational order at the liquid‐vapor interface as well as the corresponding surface tension. We systematically analyze the dependences of these quantities on the temperature and on the strength of the dipole moment of the molecules. This reveals power laws and, close to criticality, scaling behavior. Our approach, which is reliable even for large dipole moments, allows us to determine separately those contributions to the surface tension which are due to the orientational degrees of freedom.
Electric field‐induced structure changes in water‐in‐oil microemulsions: Time‐resolved Kerr effect measurements
Authors: Runge F. , Schlicht L. , Spilgies J.‐H. , Ilgenfritz G.
Published: July 2012

A percolation transition in microemulsions can be induced by high electric fields. We report on the dynamics of the processes. Comparison of time‐resolved conductivity, birefringence and light scattering measurements gives information on the structure changes. The differences of ionic and nonionic microemulsions are emphasized.
In situ imaging of monolayers on interfaces by polarization and second‐harmonic microscopy
Authors: Flörsheimer M. , Jundt D. H. , Looser H. , Sutter K. , Küpfer M. , Günter P.
Published: July 2012

A simple non‐scanning microscope for the in situ and real‐time investigation of many kinds of interfaces and ultrathin films is described. Polarization microscopy images the complex index of refraction of the sample, second‐harmonic microscopy images the second‐order optical susceptibility.
Quantum effects and orientational ordering in adsorbed layers of linear molecules
Authors: Marx D. , Sengupta S. , Nielaba P.
Published: July 2012

We study the influence of quantum fluctuations on the herringbone transition in adsorbed complete √3‐mono‐layers of diatomic molecules. Using Path‐Integral Monte Carlo simulations for rotations, we can quantify the shift of the transition temperature for a highly realistic model to describe N2 on graphite. In addition, the zero‐point motion of the librating molecules depresses the ground‐state order parameter. We compare the benchmark data to quadratic Feynman‐Hibbs effective potential simulations and to a quasiharmonic approximation. Using a simplified model for this transition, we study systematically quantum effects being relevant for lighter molecules. Depending on the rotator's rotational constant, we find re‐entrant orientational quantum melting or even the suppression of orientational order.
Mutual diffusion coefficients for the system benzene‐cyclohexene at 25 °C
Authors: Harris Kenneth R. , Dunlop Peter J.
Published: July 2012

Mutual diffusion coefficients are reported for mixtures of benzene and cyclohexene at 25 °C which have been measured using the Gouy interferometric technique. A comparison is made between this system and mixtures of benzene with perdeuteriobenzene, chlorobenzene and cyclohexane
Near‐infrared spectroscopic investigations on phase behaviour and hydrogen‐bonding of polar substances in supercritical chlorotrifluoromethane. Part II — association behaviour
Authors: Ochel Henning , Schneider Gerhard M.
Published: July 2012

The association behaviour of selected polar substances capable of self‐association in mixtures with supercritical chlorotrifluoromethane was investigated by high‐pressure near‐infrared spectroscopy. The alkanoic acids and cyclic amides investigated were dodecanoic acid, hexadecanoic acid, δ‐valerolactam, and δ‐caprolactam. The concentrations of the non‐associated molecules were determined from an evaluation of the first overtone region of O–H (∼ 1435 nm) or N–H stretching vibrations (∼ 1485 nm), respectively. The association behaviour is presented in plots of total, free, and hydrogen‐bonded molecule concentrations as a function of pressure. Furthermore, equilibrium constants Kc were determined and their density dependence is discussed, taking into account the influence of molecular properties on the association reaction in the supercritical fluid.
The relation of solvatochromism and thermochromism to the solvent dielectric constant: The basis of the ET and E'T polarity scales
Authors: Streck Christof , Richert Ranko
Published: July 2012

We have measured the thermochromism of pyridinium‐N‐phenoxide betaine and its penta‐tert‐butyl substituted derivative dissolved in MTHF together with the solvent dielectric properties in order to relate polarity scales to the dielectric constants of the solvent. Both thermochromic and solvatochromic shifts of the absorption band of the dyes can be rationalized on the basis of the MSA theory for relating the solvation free energy to the static dielectric constant. Deviations between theory and experiment in the regime of higher viscosities can be attributed to changes in the offset between absorption maximum and electronic transition energy.
Electrotransport in ionic crystals: II. A dynamical model
Authors: Janek J. , Martin M.
Published: July 2012

A microscopic model of electrotransport in semiconducting ionic crystals is described, which is based on electrostatically interacting hopping charge carriers (cation vacancies and electron holes). Formulating rate equations for the thermally activated motion of electronic and ionic defects in external fields allows for the calculation of stationary charge distributions. In the case of large differences in the mobilities of both defects an adiabatic approximation can be introduced which allows to separate the motion of electron holes and vacancies. The formal problem is identical to the solution of the Poisson‐Boltzmann equation for large defect concentrations. An expression for the charge of transport is derived which is equivalent to the Debye‐Huckel expression for the relaxation effect but includes distinct geometrical positions around a central point charge.