bluuebunny/crossref_metadata_2025 huggingface dataset:
Attraction of pure electrostatic origin between small colloids
Authors: Belloni Luc , Spalla Olivier
Published: July 2012

The interaction between two spherical colloids immersed in an electrolyte of screening constant K is studied using the recent Charge Regulation Primitive Model and the hypernetted chain integral equation. The charge of the particles is not fixed a priori but results from the adsorption of positive and/or negative ions onto the colloidal surfaces. The charge regulation condition induces new colloid‐ion and colloid‐colloid attractions which are missing in the usual Primitive Model (constant charge condition). The attractions behave at long distances as −exp (‐2Kr)/r2 for small colloids. In the case of an adsorption of only one type of ions, the attraction adds to the usual screened coulombic interaction which dominates at long distances. In the case of symmetrical adsorption of positive and negative ions, the colloids are globally neutral and attract each other even at long distances.
Binding of carboxylated starburst dendrimers to poly(diallydimethylammonium chloride)
Authors: Zhang H. , Dubin P. L. , Spindler R. , Tomalia D.
Published: July 2012

The interaction between poly(diallydimethylammonium chloride) (PDADMAQ and carboxylated starburst dendrimers (generations 0.5, 3.5, 5.5 and 7.5) was investigated over a range of ionic strength from 0.01 to 0.50 M NaCl using pH titration, turbidimetry and quasi‐elastic light scattering methods. Complex formation occurs most readily with generation 7.5, which may be attributed to its high charge density relative to the smaller dendrimers. The effects of ionic strength confirmed the electrostatic nature of the interaction, while pH titrations revealed that complex formation is stoichiometric. Analysis of pH titrations via the effect of binding on the pKa of the dendrimer carboxylic acid groups lead to estimates of the free energy of complex formation.
Influence of polyelectrolyte adsorption on the electro‐optical behavior of aerosil particles
Authors: Buleva M. , Petkanchin I.
Published: July 2012

The adsorption of polyelectrolyte, sodiumcarboxymethyl‐cellulose (Na‐CMC) on Aerosil (SiO2) particles is studied by means of electric light scattering and electrophoresis. The electro‐optical effect α increases with the rise of polyelectrolyte concentration. Simultaneously the increase of particles' electrophoretic mobility reveals the adsorption of polyion on identically charged particles. The similarity of the frequency dependence of the electrooptic effect at different polyelectrolyte concentrations is an indication that the particles' induced dipole moment is mainly determined by polyelectrolyte' counterions behaviour.

Two relaxations of the electro‐optical effect are observed at frequencies ranging from 500 Hz to 100 kHz the first relaxation is about 1 kHz, the second one ‐ in the 10 kHz region. The increase of charge density parameter ζ doesn't influence the first relaxation, but the second one becomes wider and more noticeable. According to Manning predictions the rising of ζ(ζ>1) results in the increase of the fraction of diffuse counterions. So their contribution to the induced dipole moment is more clearly demonstrated in the frequency dependence. Most probably the first relaxation of α is connected with the “bound” counterions whereas the second is due to the diffuse counterions. In the case of polyelectrolyte adsorption on the particles of the same charge sign an analogy with Manning consideration for free polyelectrolytes in solution could be drawn.
Stoichiometry and structure of polyelectrolyte complex particles in diluted solutions
Authors: Dautzenberg Herbert , Hartmann Jürgen , Grunewald Steffi , Brand Fabien
Published: July 2012

UV/VIS spectroscopy, potentiometry, viscometry, static and dynamic light scattering as well as electron microscopy were used to study the Stoichiometry and structure of polyelectrolyte complexes between Na‐poly(styrenesulfonate) and copolymers of diallyldimethylammonium chloride and acrylamide of various composition. In diluted, non‐stoichiometric solutions polyelectrolyte complex formation leads to polydisperse systems of highly aggregated, nearly spherical particles, which are stabilized by a slight excess of the major component. At the 1:1 molar mixing ratio flocculation occurs. The structure density of the polyelectrolyte complexes depends strongly on the composition of the polycations.
Surface modification by polyelectrolyte complexes
Authors: Buchhammer Heide‐Marie , Lunkwitz Klaus
Published: July 2012

Co‐operative interaction between water‐soluble polymers has been a topic of investigation world‐wide because of their importance from both scientific and practical viewpoint.

Our work is focused on the investigation of complex formation between oppositely charged polyelectrolytes and the interaction with inorganic fine particles for example negatively charged quartz powder and silicic acid. The cationic polyelectrolytes tested were poly(diallyldimethylammoniumchloride) (PDADMAC) and polyallylamine (PAA), differing in the molar mass, the molecular geometry and charge density. The anionic polyelectrolytes used were copolymers of maleic acid with propylene (MS‐P), styrene (MS‐Sty) and methylstyrene (MS‐α‐MeSty).

Two different principles of surface modification with polyelectrolyte complexes were tested. On the first hand previous prepared non‐stoichiometric complex dispersions carrying cationic excess charges were contacted to the substrate and on the other hand the polycation was preadsorbed on the oppositely charged surface before an equimolar amount of polyanion was added. Both methods show different results in the reachable surface charge. It is important to note that a synergistic effect with respect to the cationic surface charge was found in dependence on the surface charge density of the substrate, the chosen polyelectrolyte combinations and the used modification procedure. From the results it is concluded that steric factors of the polyelectrolytes are responsible for conformation and stoichiometry of the formed polyelectrolyte complexes and thus the effectiveness of charge modification with polyelectrolyte complex is also determined by the characteristics of the used polyions.
Immobilisation of biological matter by polyelectrolyte complex formation
Authors: Dautzenberg H. , Lukanoff B. , Eckert U. , Tiersch B. , Schuldt U.
Published: July 2012

The immobilisation of biological matter plays an important part in creating biologically active systems for applications preferably in biotechnological processes or in medical treatments. The immobilisation by polyelectrolyte complex formation, allowing the encapsulation of sensitive biological objects or materials without causing any damage to them, has become a powerful alternative method. In more detail experimental results on capsule formation with sodium cellulose sulphate and poly(diallyldimethylammonium chloride) as reaction compounds are reported. Capsule formation and capsule properties (morphological features, cut‐off, rate of NaCS conversion, size and mechanical stability) are looked at under polymerchemical and physicochemical aspects. The importance of osmotic effects is revealed. It is shown that the capsule properties depend not only on the chemical structure of the polyelectrolytes or the conditions of capsule preparation, but also remarkably on the polymer‐chemical characteristics of the reaction components, particularly on their molecular mass and/or molecular mass distribution.
Construction of a biochemo‐mechanical system using inhomogeneous polyelectrolyte gels with immobilized urease
Authors: Kokufuta Etsuo , Matsukawa Shingo
Published: July 2012

The present study attempts to construct a biochemo‐mechanical system using inhomogeneous polyelectrolyte gels composed of N‐isopropylacrylamide (NIPAAm) and acrylic acid (AAc) into which urease has been immobilized through physical entrapment. A redox polymerization initiated by a pair of ammonium persulfate and N, N, N′, N′‐tetramethylethylenediamine is employed to obtain gels from aqueous enzyme solutions containing the following monomers: NIPAAm, AAc, and N,N′‐methylenebis(acrylamide) (cross‐linker). The gelation was performed at several temperatures below and above the lower critical solution temperature (LCST′; ca. 33°C) of the NIPAAm polymer. All the gel samples obtained above the LCST were opaque in appearance, suggesting in‐homogeneity, whereas polymerization below the LCST yielded conventional transparent gels. The observed urea‐induced swelling at 34°C was much faster in the former gels than in the latter. In addition, little size‐dependent swelling‐shrinking kinetics were observed in the inhomogeneous biochemo‐mechanical gels. This was distinct from the swelling‐shrinking kinetics of conventional gels. Therefore, it can be suggested that inhomogeneous polyelectrolyte gels are useful in the construction of biochemo‐mechanical systems exhibiting enzymatically induced faster swelling‐shrinking changes.
Dielectric studies of octyloxy‐cyanobiphenyl (8OCB) under high pressure
Authors: Brückert T. , Urban S. , Würflinger A.
Published: July 2012

The static and complex permittivity of octyloxy‐cyanobiphenyl (8 OCB) has been measured for the smectic, nematic and isotropic phase as a function of temperature and pressure. The main part of the work is concerned with the study of ϵ∥, the component of the permittivity parallel to the director n, and its frequency dependence up to 13 MHz, yielding the dielectric relaxation time τ∥, connected with the rotation of the molecules around their short axes. The temperature and pressure dependence of τ∥ allows to calculate the activation enthalpy, Δ≠H∥, and activation volume, Δ≠V∥, respectively. The activation parameters for the nematic phase (Δ≠H∥ = 75‐55 kJ/mol, decreasing with increasing pressure, Δ≠V∥ = 65‐45 cm3/mol, decreasing with increasing temperature) are similar to previous results for octyl‐cyanobiphenyl (8 CB), however, for the smectic Ad phase (Δ≠H∥ ≈︁ 40 kJ/mol, Δ≠V∥ = 40‐50 cm3/mol) the p, T‐dependencies are opposite to 8 CB. A comparison of the relaxation times for the isotropic and nematic phase enables us to estimate retardation factors and the nematic potential q in the frame of theories of Meier‐Saupe and Coffey et al. With the aid of literature data for the order parameter S the linear relationship q ∼ S was checked.
Diffusion of interacting lattice gases on homogeneous surfaces
Authors: Uebing Christian , Gomer Robert
Published: July 2012

Tracer and chemical surface diffusion coefficients, D* and D respectively, were studied on a homogeneous surface of square symmetry by means of Monte Carlo modeling. D was determined by the fluctuation autocorrelation function method and from the Kubo‐Green equation. Both techniques yield identical results. Simulations were carried out for a lattice gas model with repulsive nearest neighbor interactions affecting both adsorption sites (ϕNN) and saddle points (ϕ*NN) of the periodic potential. The phase diagram of the lattice gas model shows c(2×2) ordering at low temperatures θ≈︁0.5. It was found that both types of interactions, ϕNN and ϕ*NN, strongly affect surface diffusion. The effects are most pronounced at low tempratures T and high surface coverages θ where the adatoms are closely together. It was found that raising the saddle point energies by ϕ*NN counteracts and may totally compensate for the effect of repulsive nearest neighbor interactions ϕNN.
Simultaneous small‐ and wide‐angle X‐ray diffraction during the main transition of dimyristoylphosphatidylethanolamine
Authors: Rappolt Michael , Rapp Gert
Published: July 2012

The main transition of dimyristoylphosphatidylethanolamine (DMPE) dispersed in excess water has been investigated by simultaneous small‐ and wide‐angle X‐ray diffraction during heating and cooling scans. At scan‐rates of 0.6°C/min and 0.1°C/min the transition has at least three components during heating, and four components during cooling. Amplitude and thermal width of these components are similar to those found in calorimetric experiments (B.Z. Chowdhry, G. Lipka, A. W. Dalziel, and J. M. Sturtevant, Biophys. J. 45, 901‐904 (1984); H. Yao, I. Hatta, R. Koynova, and B. Tenchov, Biophys. J. 61, 683‐693 (1992)). It is suggested that the different components of the transition from the gel to the liquid crystalline phase and vice versa are attributed to different steps of a cluster growth mechanism in liposomes. Initially the growth proceeds primarily radially, most likely along defects, and not shell by shell. A model is presented to explain (1) the sequence of steps, (2) their relative width and cooperativity and (3) the hysteresis of the transition.
On the rate constant for non‐steady state nucleation at solid surfaces
Authors: Tomellini Massimo
Published: July 2012

The rate constant for non‐steady state nucleation at solid surfaces has been evaluated in the case of very small size of the critical nucleus. For this purpose a rate equation approach has been employed in which elementary steps are the attachment and the detachment of both ad‐monomers and gas monomers to and from the subcritical clusters. It is shown that if equilibrium is established between gas‐ and ad‐monomers the rate constant can be written in a highly simplified form. In this case a detailed computation indicates the apparent activation energy for nucleation to depend on the ratio between the surface diffusion coefficient of ad‐monomers and the flux of gas atoms incoming at the surface. The rate constant exhibits a power law dependence on the flux of monomers whose exponent is related to the size of the critical cluster. Both the physical cases of weak adsorption and of total condensation of the ad‐atoms at the nucleation sites have been considered.
Some results on the mechanism of the reaction between O(3P)‐atoms and HOCl. An experimental and Ab initio model study
Authors: Schindler Ralph N. , Dethlefs Jan , Schmidt Mark
Published: July 2012

The rate constant for the title reaction was redetermined using discharge flow technique and mass spectrometric measurements of HOCl consumption. The overall rate constant k = (1.7±0.3)×10−13 cm3 molecule−1 s−1 was obtained and found to be practically independent of temperature in the range 213 K≤T≤298 K. In experiments using 18O atoms the time dependence in the formation of the products 18O16O, HC1 and Cl2 was determined. Based on the experimental data available it is proposed that the reaction occurs via an intermediate complex mechanism but it could not be decided by which primary steps the reaction is initiated.

Ab initio model calculations were carried out in an attempt to quantify conceived reaction pathways. Structures and energetics of the intermediates were computed. On the basis of these calculations it is suggested that Cl abstraction from HOC1 should be regarded as the preferred initiation step. The O‐atom attack leads to the formation of an intermediate HOClO. Alternative reaction pathways, like H abstraction from HOCl by O‐atom attack, or a mechanism in which HO2 and Cl are formed were found to be less probable. In the present calculations no support could be found for the thermodynamically most preferred reaction route to contribute to product formation. Structure and energy of the intermediate HOC1O are computed.
Surface order induced ferroelectricity in ultrathin films of the smectic a phase of a chiral liquid crystal
Authors: Hoffmann E. , Stegemeyer H.
Published: July 2012

In free standing films of the smectic A phase of a chiral liquid crystal ferroelectric switching has been observed. The polarization charge obtained by the field switching does not depend on the number of smectic A layers. The results confirm the molecular tilt in the boundary layers of the film caused by surface ordering.
Sequential electrodeposition of silver and bismuth on a gold surface
Authors: Schröter C. , Solomun T.
Published: July 2012

Sequential electrodeposition of Ag and Bi from a single electrolyte on Au (111) was studied by means of voltammetry and ion scattering spectroscopy (ISS). Silver was electrodeposited first under diffusion control. Subsequently, bismuth was deposited under potential sweep conditions. Underpotential deposition of BI on the gold surface modified with five Ag monolayers takes place similar to the deposition on the Ag (111) electrode. The deposited Bi can be electrodissolved completely with Ag remaining on the surface. However, the voltammetric characteristics of this process are different from the one in the case of Bi on the (111) surface of a silver single crystal. The ISS data suggest that this might be due to intermixing at the Ag/Bi interface occurring subsequent to the formation of the initial Bi on Ag structure on Au(111).
Multicomponent diffusion of sodium alginate solutions with added salt. II. Charged vs. Uncharged system
Authors: Paradies H. Henrich , Wagner Dirk , Fischer Wulf R.
Published: July 2012

Diffusion coefficients are reported for dilute aqueous solutions of sodium alginate, and for three compositions of the ternary system comprising of sodium alginate/sodium chloride/water at 20°C applying the conductimetric method. From binary transport data the ternary diffusion coefficients for alginate of added salt (NaCl) can be qualitatively calculated. Due to electrostatic interactions between the ions the diffusive flow of the alginate polyelectrolyte and added salt reveal strong coupling. At pH>5.0 (20°C) and ionic strength of 0.015 M NaCl each mole of diffusing alginate cotransports approximately 210 moles of NaCl. Coupled flow of NaCl ceased if the solution pH is approaching pH 5.5, close to the isoelectric point of alginate (pH 5.4). Between pH 4.5–5.0 the coupled transport of NaCl is governed by the diffusion of the protonated alginate concentration gradient due to the diffusion induced electric field along the neutral alginate. At acidic pH (3.5–4.0) diffusing alginate generates a counter flow of NaCl due to additional bound protons, yielding a net positive charge hence the D21‐value is large and positive.
On the uniqueness of stratification‐induced structural transformations in confined films
Authors: Schoen Martin
Published: July 2012

This article is devoted to an investigation of structural transformations which occur in molecularly thin films confined between planar structured and unstructured rigid solid surfaces as the number of fluid strata parallel with the walls changes under conditions of fixed chemical potential μ and temperature T. The transformations become manifest as periodic maxima in the transverse isothermal compressibility k∥ computed in grand canonical ensemble Monte Carlo simulations via fluctuations in film density. The transformation occurs at nearly identical characteristic separations sz of the surfaces regardless of whether these are discrete (i.e., composed of individual atoms) or smooth in transverse dimensions. The transformation is caused mainly by confinement to spaces of molecular dimension and is unique, that is independent of details of the film‐wall interaction. Because of the inhomogeneity of a film between structured surfaces in transverse dimensions a definition of k∥ in terms of density fluctuations is precluded in general. However, by considering only restricted thermodynamic transformations on a length scale defined in units of the lattice constants characterizing the wall structure, such a definition is possible introducing k∥ as a density fluctuation‐related quantity in a coarse‐grained sense. Variations of the local density of the film around the transition points suggest to perceive the phase transition as stratification‐induced, because it happens after the new stratum has begun to form.
Isothermal Switching of conductivity in microemulsions via photodimerization of acridizinium bromide [1]
Authors: Nees Dieter , Cichos Ulrike , Wolff Thomas
Published: July 2012

Microemulsions composed of Aerosol OT (AOT), isooctane, and water in the mass ratio 1:1. 54:0.75 exhibit percolation, i.e., transition from a w/o to an o/w microemulsion, at 33 °C as revealed by the appearance of conductivity. In the presence of 0.01 mol/dm3 of acridizinium bromide the percolation temperature increases to 38 °C. Irradiation of this mixture with glass‐filtered light leads to a further rise of the percolation temperature to 43 °C. Thus, the system can be switched from conducting to non‐conducting upon irradiation at between 38 and 43 °C.
An improved thermodynamic approach to the stability of multi‐component silicate glasses in aqueous solutions
Authors: Conradt Reinhard , Geasee Pisit
Published: July 2012

A rate equation is developed by which the dissolution rates of multicomponent silicate glasses in diluted aqueous solutions can be calculated as a function of pH, CO2 partial pressure, and salinity. Gibbs free energies of hydration are derived by treating the aqueous solution as a diluted system of aqueous species of the various cations in the glass, and by treating the glass as a mixture of the constitutional phases taken from its basic phase diagram. Beside the free energies, the amounts of H+ and OH− absorbed at the glass surface are taken into account as rate determining factors. Calculated dissolution rates of silica, A type, E type, rock, and slag glass fibres agree with experimental values within ±30% on a linear scale.
Crystallization processes of cordierite glasses
Authors: Morinaga Kenji , Takebe Hiromichi
Published: July 2012

To prepare α‐cordierite glass ceramics, we demonstrate two types of phase diagrams of a composition 2MgO·2Al2O3·5SiO2 with time courses. One is the continuous‐cooling‐transformation (CCT) diagram; the other is the temperature‐time‐transformation (TTT) diagram. At ∼ 1273 K, μ‐cordierite is crystallized as the primary phase and then it transforms to α‐cordierite with a lath‐like martensite transformation. The volume expansion derived from this transformation results in a lot of cracks in crystallized glasses. Since the addition of MgF2 for the substitution of MgO (ca. 5%) suppresses the μ‐to α‐cordierite transformation but promotes the direct crystallization of α‐cordierite from glass, we can prepare α‐cordierite glass ceramics without cracks. In this paper, we point out the needs and usefulness of CCT and TTT diagrams for glass ceramics processing.
Nucleation sites at cordierite glass surfaces
Authors: Müller R. , Reinsch S. , Völksch G. , Heide K.
Published: July 2012

The nucleation density, N, of high‐quartz solid solution crystals (“μ‐cordierite”) at surfaces of cordierite glass (2 MgO·2Al2O3·5SiO2) was studied by optical and electron microscopy for differently damaged surfaces prepared and thermally treated in controlled ambient atmosphere.

(i) Sharp tips and edges are dominating nucleation sites at mechanical damaged cordierite glass surfaces. These sites are privileged due to a substantial reduce of the elastic energy that contributes to the work of forming a critical nucleus within the surrounding glass phase. (ii) Solid foreign particles are dominating nucleation sites at smooth surfaces. Oxide particles, dusted on to the glass surface prior to heat treatment, increase N in most cases. Their nucleating efficiency (ZrO2 (monoclinic)>(ZrO2 (tetragonal)>Al2O3 ≈ Fe2O3>CeO2>MgO) indicate their role as chemically stable nucleating substrates. Non‐oxide particles have no influence (SiC, Si3N4) or even suppress surface nucleation (WC, W) indicating chemical interaction with the glass. (iii) Both, no strong influence of ambient humidity on N and similar minimum values of N, Nmin≈10−8 μm−2, for free air and vacuum experiments indicate minor nucleation activity of flat pristine glass surfaces even in contact with air. On the other hand, N is influenced by the sample‐crucible geometry.
The influence of the iron concentration and the Fe2+/Fe3+ redox ratio on the crystallisation of Bioverit II
Authors: Kasten C. , Carl G. , Rüssel C.
Published: July 2012

Transition metal ions do not solely influence the optical properties of glasses but also their crystallisation behavior. In the case of iron in a mica glass ceramic, Fe3+ leads to smaller mica‐aggregates and suppresses the crystallisation of indialith. In glasses melted under reducing conditions, Fe2+ is formed which is incorporated into the indialith and leads to a preferred crystallisation of this phase. Iron does not act as a simple colouring additive but influences the whole nucleation and crystallisation process.
III. Electrochemistry in Glasses and Melts. Glass electrodes: Why and how they function
Authors: Baucke Friedrich G. K.
Published: July 2012

Subsurface concentration profiling by Ion Bombardment for Spectrochemical Analysis (IBSCA) and Nuclear Reaction Analysis (NRA) combined with other methods yielded information on the ionic processes at and in glass electrode membranes and results in the mechanism (“dissociation mechanism”) of glass electrodes. The primary step is the formation of a phase boundary equilibrium between functional groups, e.g. siloxy, at the glass surface and hydronium or alkali ions in the solution. It determines the potential of the glass due to the charge density established at the glass surface by the dissociated form of the surface groups, e.g. SiO−, and the surface activities of the acidic or salt forms of the surface groups, e.g. SiOH and SiOM, respectively. This inseparable connection of solution‐dependent potential and “surface coverage” was verified by electrolytic migration experiments. The concentration gradients thus caused below the glass surface lead to an ionic interdiffusion in the subsurface glass range (if the ions attached to the surface groups are not hindered sterically to enter the glass), which is the first step of glass corrosion, and to a diffusion voltage, which is part of the overall membrane potential. Quantitative expressions are given, and it is shown that, in principle, the response of glass electrodes is below “ideal”, i.e. smaller than RT(In 10)/F, which explains the well known sub‐Nernstian response of pH glass electrodes. Two new sodium errors were found. Construction and operation of glass electrodes are briefly sketched as an introductory basis. The reason for the long existence of the purely thermodynamic “ion exchange theory” is analysed.
Voltammetry in silicate and borosilicate melts
Authors: Claußen Olaf , Rüssel Christian
Published: July 2012

With the aid of square‐wave‐voltammetry, redox equilibria of various multivalent elements were studied in a soda‐lime‐silicate and a borosilicate glass melt in the temperature range of 600 to 1300°C. The peaks in the current‐potential curves could be attributed to certain redox couples. The peak potentials measured dependend linearly on temperature proving that both standard enthalpy and standard entropy possess constant values within the temperature range studied. The peak potentials measured in the silicate and the borosilicate melt were in fairly good agreement. A systematic shift caused by the higher alkali content of the borosilicate glass could not be observed.
IV. Transport Phenomena, Properties of Glass Surface and Corrosion. Ion and polaron conducting glasses
Authors: Cramer C.
Published: July 2012

Conductivity spectra, σ(ω), covering wide frequency ranges up to the mid infrared, have been taken of various glasses at different temperatures. The systems studied include the ion‐conducting glasses 0.30 Na2O·0.70 B2O3, 0.30 Li2O·0.70 B2O3 and B2O3·0.56 Li2O·0.45 LiBr as well as the polaron conducting glass 0.2 P2O5·0.8 (0.89 V2O5·0.11 V2O4). In the case of the ion‐conducting glasses it is possible to separate vibrational and hopping spectra from each other. The resulting hopping spectra display high‐frequency plateaus; in the dispersive regime, two power‐law exponents are observed, one being smaller, the other larger than unity. In contrast, the dispersive conductivity of the polaron conducting glass shows a simple single‐power‐law behavior with an exponent smaller than one. The interpretation of the spectra includes the idea of different “target” sites for the mobile species. A model concept for ion and polaron transport in glasses is proposed.
Oriented crystallization of fresnoite in an electric field
Authors: Keding Ralf , Rüssel Christian
Published: July 2012

A glass melt with the composition of Ba2TiSi2O8·0.75 SiO2 was soaked at 1300°C. This did not lead to any crystallization. A current of 50 mA applied between the platinum crucible which acted as the anode and a platinum cylinder inserted to the melt as the cathode led to a potential of 1.2 V. This resulted in a crystallization of fresnoite at the cathode which continues for around 10 min until the crystallites reached the anode. The resulting glass ceramic was highly oriented and the microstructure was composed by fairly long needles consisting of fresnoite crystals. The long axis of the needles is the crystallographic c‐axis of the fresnoite. It is a polar axis and oriented parallel to the electric field. The nucleation process caused by current flow supposedly is an effect of the Ti3+ formed. Here, the viscosity should be decreased in the vicinity of the cathode and therefore the nucleation is enabled.
Sn+‐implantation and radiation‐induced structural modifications in amorphous SiO2
Authors: Angermann T. , Dunken H. H.
Published: July 2012

The structural damage produced by Sn+‐implantation into high purity silica substrates with doses of 1.1–2.0×1017 ions/cm2 at an acceleration voltage of 300keV has been analyzed by infrared reflexion spectroscopy (IRR), UV‐VIS spectroscopy, Rutherford backscattering spectroscopy (RBS), X‐ray diffraction and transmission electron microscopy (TEM). Densification, bond distortion and structural disorder of the implanted samples have been investigated. X‐ray diffractograms and TEM observations proved the formation of nanosize β‐Sn‐colloides.
V. Physicochemical Methods of Glass Characterization. Connectivities and cation distributions in oxide glasses: New results from solid state NMR
Authors: van Wüllen Leo , Gee Becky , Züchner Lars , Bertmer Marko , Eckert Hellmut
Published: July 2012

Modern solid state nuclear magnetic resonance (NMR) techniques afford powerful experimental strategies for elucidating detailed structural information in noncrystalline materials. While previous research emphasis has been on the identification and quantification of local environments (short‐range‐order), primarily by using the technique of magic‐angle spinning (MAS) NMR, correlations beyond the nearest neighbor coordination sphere (intermediate‐range order) can be studied by more sophisticated methods. This contribution focuses on recent advances made for a variety of oxide glasses, using methods of dipolar spectroscopy: Connectivities among the structural building blocks present in sodium aluminoborate glasses have been exposed using 11B{27Al} and 27Al{11 B} rotational echo double resonance (REDOR) NMR. Similarly, 29Si{31P} and 29Si{7Li} REDOR data form the basis of a structural model integrating six‐coordinated silicon into the network structure of alkali silicophosphate glasses. The spatial cation distributions in sodium silicate glasses are studied by 23Na spin echo decay spectroscopy, offering experimental evidence for inhomogeneous cation distributions at low alkaline contents. Finally, for mixed alkali sodium lithium silicate glasses, 23Na{7Li} spin echo double resonance (SEDOR) and 29Si{23Na} and 29Si{7Li} REDOR spectroscopies provide important experimental criteria for testing hypothesized relative Na‐Li cation ordering scenarios.
Structure of vitreous KPO3 studied by neutron and X‐ray diffraction
Authors: Hoppe U. , Walter G. , Stachel D. , Hannon A. C.
Published: July 2012

The gain of information about the glass structure obtained by RMC simulations on the basis of neutron and X‐ray diffraction results is demonstrated by vitreous KPO3. Details of the first neighbour P‐O peak confirm the existence of ring and chain structures which are formed from two‐fold linked PO4 units. The separation distance of these anionic molecular structures is determined by the dimension of the large K+ cations. The mutual arrangements of the modifier cations in their oxygen polyhedra form an interpenetrating substructure which surrounds the various forms of linked PO4 tetrahedra.
Cation ordering scenarios in mixed alkali silicate glasses. Experimental constraints from 23Na{6Li} spin echo double resonance NMR
Authors: Gee Becky , Eckert Hellmut
Published: July 2012

The spatial arrangement of sodium and lithium ions in mixed‐alkali silicate glasses of composition [(Li2O)1‐y(Na2O)y,]0.4[SiO2]0.6 (y = 0.25, 0.50 and 0.75) is explored by 23Na{6Li} spin echo double resonance (SEDOR) NMR spectroscopy on isotopically labelled materials. The results are discussed within the context of two basic models for the spatial cation distribution, both of which are calculated with the constraint of resulting in the same cation density as experimentally measured for the glasses: The first scenario considers a homogeneous distribution of the cations by arranging them at regular distances on a cubic lattice. For this base model, a statistical mutual arrangement of lithium and sodium is in fairly good agreement with the experimental data. The second scenario models a clustered distribution by fractionally occupying the cation sites of the Na2O lattice in a random fashion. If this base model obtains, the experimental NMR results indicate preferential interactions among like cations. Approximate agreement with the experimental SEDOR decay curves can be obtained by assuming a flat distribution function of MNa‐Li2 values, ranging from zero to M20, the average second moments calculated for a statistical mutual distribution of Li and Na ions. This model also gives satisfactory fits to previously published 23Na{7Li} SEDOR data on compositional analogous glasses with the natural isotope distribution.
Synthesis and characterization of oxycarbide glasses in the BaSiOC‐system and the influence of aluminum on the ability to incorporate carbon into the glass network
Authors: Lansmann V. , Hoffbauer W. , Wartner N. , Mader W. , Jansen M.
Published: July 2012

So far, only a few investigations about oxycarbide glasses prepared by a melting process are reported and no evidence has been provided for carbon being incorporated into the glass network. The present work describes the preparation and characterization of glasses in the BaSiOC and BaSiAlOC system prepared from the melt. The glasses were characterized by X‐ray diffraction, transmission electron microscopy, differential scanning calorimetry and 29Si‐ and 27Al‐MAS‐NMR Spectroscopy. By identifying SiO3C units in the BaSiOC system the first spectroscopic proof is given that in oxycarbide glasses prepared by a conventional melting process carbon is incorporated into the glass network. The substitution of silicon by aluminum results in a tighter network, which was unable to incorporate carbon.
Light induced nonequilibrium effects in gases
Authors: Schramm B. , Wörner T.
Published: July 2012

It is possible to disturb the equilibrium velocity distribution of molecules in a gas by absorption of narrow band laser light. This leads to light induced transport phenomena. We report on experiments, where we have measured the pressure difference caused by light induced viscous flow and where we have separated the two nuclear spin modifications of CH3F with the help of light induced drift.
Two‐dimensional nucleation initiated by athermal clusters
Authors: Donner C. , Pohlmann L. , Baumgärtel H.
Published: July 2012

The prepolarisation potential influences the two‐dimensional nucleation kinetics of adsorbed neutral molecules on a mercury electrode in the system 5‐bromocytosine/Na2SO4. It was shown that for prepolarisation potentials located near the phase transition potential a significant amount of large clusters is formed, which after the jump into the condensation region become overcritical nuclei with an athermal distribution. Significant differences exist in the kinetics at the cathodic and the anodic edge of the condensation region, respectively. This indicates that the potential dependence of the adsorption isotherm of the neutral molecules can not be symmetrical, as supported usually. These investigations show furthermore that the nucleation rate is not solely a function of the applied potential, but depends also on the prepolarisation conditions.
Highly dimerizable radical cation of 3,3′,5,5′‐tetramethylbenzidine
Authors: Awano Hiroshi , Ichihara Osamu , Sawada Kazutaka , Ohigashi Hiroji
Published: July 2012

Cation radical salts of 3,3′,5,5′‐tetramethylbenzidine (TMB) were studied in terms of dimerization of the radical cation, and compared with the salts of other aromatic diamines, including Wurster's blue perchlorate. ESR spectra of several TMB salts were measured in solid‐state, and analyzed by the singlet‐triplet model for a radical dimer. The singlet‐triplet energy separation has been obtained as 0.15 eV for (TMB)ClO4. The dimerization of the TMB radical cation in acetonitrile solution of (TMB)ClO4 was estimated from ESR and visible spectral results. In consequence, (TMB)+. is highly dimerizable in solution, compared with the systems of other diamines.
Electrocatalysis of the quinone/hydroquinone system by electrodes coated with substituted polyaniline
Authors: Malinauskas Albertas , Holze Rudolf
Published: July 2012

Polymer films derived from N‐methylaniline (NMA), N(3‐sulphopropyl)‐aniline (NSPA), 2‐ and 3‐methylanilines (2‐MA and 3‐MA), and 2,3‐, 2,5‐ and 2,6‐dimethylanilines (2,3‐DMA, 2,5‐DMA and 2,6‐DMA), as well as of some copolymers, were obtained on a platinum electrode in acidic solution by potential cycling. Electrocatalytic properties of the resulting polymer coated electrodes towards the hydroquinone‐benzoquinone redox couple were investigated. The following sequence of catalytic activity was found: poly(2‐MA)>polyNMA = copoly (2‐MA+3‐MA) > copoly(NMA+NSPA) > polyNSPA>poly(3‐MA). With respect to the stability of catalytic effects observed at prolonged potential cycling, the following sequence can be drawn: poly(2‐MA) > polyNSPA≫copoly(2‐MA+3‐MA) = poly(3‐MA) > copoly(NMA+NSPA) > polyNMA. Thus, poly(2‐MA) was found to be the most effective and stable electrocatalyst in the redox couple investigated. The polymers derived from dimethylanilines were found to inhibit this redox process.
Application of a purely physical model (DISQUAC) to binary mixtures of phenol and organic solvents
Authors: Gonzalez J. A. , de la Fuente I. Garcia , Cobos J. C.
Published: July 2012

A whole set of literature data on phase equilibria, vapor‐liquid equilibria, VLE, liquid‐liquid equilibria, LLE, and solid‐liquid equilibria, SLE, and on molar excess Gibbs energies, GE, molar excess enthalpies, HE and on activity coefficients at infinite dilution for phenol + organic solvents mixtures are examined in terms of the DISQUAC group contribution model. The interchange coefficients for OH(phenol)/aromatic; OH(phenol)/aliphatic and for OH(phenol)/C6H12 interactions are reported.

DISQUAC yields a good representation of VLE, GE and HE, as well as of the temperature dependence of GE. DISQUAC predictions on SLE are similar to those encountered in other alcoholic solutions previously investigated, and are slightly worse than those given by the mean association number theory. LLE data are critically reviewed. The necessity of different third interchange coefficients for the OH(phenol)/aliphatic interactions in the series phenol + n‐alkanes for the longer n‐alkanes in order to improve LLE predictions is discussed. The larger discrepancies are found when predicting activity coefficients at infinite dilution.
The vapor composition and vapor pressure of ZnSe from a modified Knudsen technique between 1190 and 1310 K
Authors: Schönherr E. , Freiberg M. , Siche D. , Hartmann H.
Published: July 2012

Solid ZnSe is evaporated from a Knudsen cell in vacuum. The effective molecular weight of the ZnSe vapor is directly determined by weighing the cell with and without effusion taking place. The rate of effusion is adjusted by a moveable furnace. An effective molecular weight of 135 ± 5 g/mol is found for temperatures between 1190 and 1310 K. The weight indicates the complete dissociation of the sublimed ZnSe into Zn and Se2 vapor. In that temperature range, the total equilibrium vapor pressure of solid ZnSe is estimated from the recoil force according to \documentclass{article}\pagestyle{empty}\begin{document}$ \log _{10} (P/{\rm kPa}) = - (12896 \pm 96){\rm K}/T + (9.19 \pm 0.08). $\end{document}
Synthesis and characterization of thiol‐stabilized CdTe nanocrystals
Authors: Rogach A. L. , Katsikas L. , Kornowski A. , Su Dangsheng , Eychmüller A. , Weller H.
Published: July 2012

In order to expand the range of high‐quality nanosized semiconductor materials that can be obtained as quantum dots through a wet chemical route a series of oxidize‐stable CdTe nanoclusters with narrow size distributions and extremely small particle sizes ranging from 1.3 to 2.4 nm has been prepared in aqueous solution using 2‐mercaptoethanol and 1‐thioglycerol as stabilizers. It has been investigated by means of UV‐vis absorption and photoluminescence spectroscopy, X‐ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and energy dispersive x‐ray analysis (EDX).
Adsorption and phase formation of uracil derivatives on gold and silver single‐crystal electrodes
Authors: Hölzle M. H. , Kolb D. M. , Krznarić D. , Ćosović B.
Published: July 2012

The adsorption of uracil, 6‐methyluracil, 5‐methyluracil (thymine) and 5,6‐dimethyluracil from aqueous solutions on Au(111) and Ag(111) has been investigated by cyclic voltammetry, capacity measurements and current transients, to elucidate the role of the electrode surface and of the intermolecular forces in the formation of ordered adlayers. From the calculated free adsorption enthalpies stability sequences for the condensed physisorbed phase were established. Our data show that the properties of the physisorbed adlayer are strongly influenced by the intermolecular forces, whereas in the chemisorbed state the influence of the substrate becomes dominant. For the chemisorbed molecules on Au(111) electrosorption valencies were estimated, which indicate an appreciable charge transfer.
Pressure driven transport across a cation exchange membrane in contact with mixed aqueous electrolyte solutions
Authors: Hahn O. , Woermann D.
Published: July 2012

Filtration experiments with phenolsulfonic acid‐formaldehyde cation exchange membranes are carried out with aqueous solutions containing two electrolytes with a common anion: HCl/NaCl, HCl/CaCl2and NaCl/SrCl2. The concentration difference of each electrolyte between the high pressure phase and the filtrate in the stationary state has the same sign as the reflection coefficients of the electrolytes in the mixtures determined in independent experiments. This confirms theoretical predictions. Corresponding experiments with Nafion membranes show the influence of unstirred layers on the sign of the concentration difference in filtration experiments.
Metastable crystallization of LaZr2F11
Authors: Aasland S. , Julsrud S. , Grande T.
Published: July 2012

Fusion and crystallization of the compound LaZr2F11 were investigated by differential thermal analysis and powder X‐ray diffraction. The stable modification of LaZr2F11 was observed to melt congruently at 789±4°C. The melt was easily supercooled past the melting point, before a metastable phase, β‐LaZr2F11, crystallized. On further cooling β‐LaZr2F11 went through an exothermic solid‐solid phase transition to the stable modification α‐LaZr2F11. No solid‐solid phase transition was observed during reheating of α‐LaZr2F11. The melting point of β‐LaZr2F11 was observed approximately 10 K below the melting point of α‐LaZr2F11. β‐LaZr2F11 was confirmed metastable at all temperatures, but nucleates more readily from the supercooled melt than the stable modification α‐LaZr2F11.
Networks of anharmonic resonance systems in the rovibrational overtone spectra of the quasilinear molecule HCNO
Authors: Albert Sieghard , Winnewisser Manfred , Winnewisser Brenda P.
Published: July 2012

The infrared spectrum of fulminic acid, HCNO, has been measured in the range 700‐7000 cm−1 with a Bruker IFS 120 HR interferometer. More than 130 new vibrational levels have been identified. Power series coefficients of these levels are given. Each vibrational level with its rotational levels is locally or globally perturbed. It was possible to classify most of the interactions into a grand network of Coriolis‐ and/or Fermi‐type resonance systems by using the previously known basic resonance systems 00010/00002 and 00100/00004. In addition, a new basic resonance for HCNO could be identified in the system 00015/01000/00103. As a consequence of the many interactions many so called “resonance‐enhanced” rovibrational subbands have been assigned. The identification and partial analysis of the resonance systems have been carried out, first with the help of different presentations of reduced term values and second by determining the J‐value separation between e and f crossing points. In this paper, the resonance systems 01100/01004/00203/00115 and 00014/00110/00102, which are combinations of the above mentioned basic resonance systems, will be discussed. Some further resonance systems that can be deduced from these are discussed in detail, too.
Photosynthese und Photorezeption in Halobakterien
Authors: Oesterhelt Dieter
Published: July 2012

The photobiology of Halobacteria is reviewed here. Furthermore, the functions of halobacterial retinal proteins as ion pumps for photosynthesis and as sensors mediating phototaxis are described. The well‐characterized transport mechanism of bacteriorhodopsin allows the suggestion of a general functional model of all halobacterial retinal proteins due to their structural similarities. Experimental findings showing the respective interconversions of proton‐ and chloride (halide)‐pumps, of outward‐directed to inward‐directed pumps and of sensors to pumps confirm this model. From these findings a general concept of ion translocation is derived and described as the “IST” model.
Photosynthetic antennae. Photosynthetic light‐harvesting
Authors: van Grondelle Rienk , Monshouwer René , Valkunas Leonas
Published: July 2012

The peripheral light‐harvesting complex of the photosynthetic bacterium Rhodopseudomonas acidophila (LH2) and the major plant light‐harvesting complex LHCII have a very similar function: to absorb solar photons and to transfer the electronic excitation to the pigments surrounding the reaction center, the so‐called ‘core’. Nevertheless, their structures exhibit a dramatically different arrangement of the pigments. In LH2 the bacteriochlorophyll molecules are arranged in a highly symmetric ring, while in LHCII the positioning of the chlorophylls is very irregular. In both complexes the average distance between the pigments is 1 nm or less and, as a consequence, the electronic interaction between the pigments is strong ( > 100 cm−1). Therefore, the excitation transport in these photosynthetic light‐harvesting systems can not be described by a simple Förster type transfer mechanism, but new or other transfer mechanisms may be operative, for instance a mechanism in which the excitation is to some extent delocalized. Crucial parameters are the strength of the electronic coupling, the amount of energetic disorder and/or heterogeneity and the nature and strength of the interactions of the pigments with the protein. Here we will discuss the current status of the field of photosynthetic energy transfer in particular for LH2. We will evaluate a few simple models that contain some of the essential ingredients to describe the process of energy transfer and finally we will discuss some of the perspectives in this scientific field.