bluuebunny/crossref_metadata_2025 huggingface dataset:
A Kinetic Analysis of γ‐Aminobutyrate Aminotransferase in Presence and Absence of Inhibitors
Authors: Porcelli Fernando , Scibona Giancarlo , Botrè Francesco , Lorenti Giampiero , Mazzei Franco , Botrè Claudio
Published: July 2012

The kinetics of the reaction catalyzed by γ‐aminobutyric acid transaminase (GABA‐T) is studied both in the absence and in the presence two inhibitors: n‐dipropylacetate (n‐DPA) and 4‐amino‐2‐azide‐butyric acid (GABA azide). A novel kinetic model is proposed, that is based on an experimentally derived rate equation, which describes the kinetics of the transamination process accounting for the competitive inhibition of the ketoacid and of the added inhibitor (n‐DPA, GABA azide). The consequence of the ketoacid inhibition on the primary and secondary double reciprocal plots of the initial velocity against the substrates concentration is examined. The kinetic parameters which describe the rate of the transamination reaction are derived and compared with data reported in the literature. The higher inhibition power of GABA azide with respect to n‐DPA is also assessed and discussed.
Chemical electrooptics and linear dichroism of polyelectrolytes and colloids
Authors: Kakorin Sergej , Neumann Eberhard
Published: July 2012

Recently the controversial discussion on the reliability of electrooptical relaxation data of polyelectrolyte systems has been revived. It can be shown that chemical‐conformational contributions, for instance, to the dichroitic absorbance changes are exactly given by ΔACH=(ΔA∥+2·ΔA⊥)/3, where ΔA∥ and ΔA⊥ are the measured at the light polarization modes σ = 0° (∥) and σ = 90° (⊥), respectively. Alternatively, ΔACH=ΔAσ*, where σ* = 54.7° is the magic angle (for small absorbance changes). If ΔA∥ is measured at the various σ‐polarization modes according to ΔAσ cos2 σ+ΔA⊥ sin2 σ, the exact value of ΔACH is readily obtained. On the other hand, the linear dichroism ΔA = ΔA‐ΔA=ΔA∥‐ΔA∥+(ΔA‐ΔA can only be determined as an approximation of the difference ΔA−=ΔA∥‐ΔA⊥, if ΔA and ΔA are small or approximately equal.
A new route to polyelectrolytes: Radical initiation by the redox system Ce(IV)/sulfonic acid (sulfonate)
Authors: Rosengarten L. , Tauer K.
Published: July 2012

Radical polymerization is the most commonly employed polymerization technique for the preparation of water‐soluble polymers. Unfortunately, not all water‐soluble monomers readily undergo radical homopolymerization in water. Here we report on a new redox‐initiator system for starting radical polymerizations in aqueous media. The initiator system consists of at least two components. One component (A) must contain an organic sulfonate or sulfonic acid, the other one is tetravalent Cerium. Results are presented for the following cases, which differ with respect to the properties of the component A:

I) If A is saturated it acts only as a reducing agent of the initiator system which is capable of starting radical polymerizations in the water phase. In this case the rate of polymerization is higher the higher the water solubility of the monomers.

However, if A is an unsaturated sulfonic compound (M) the reaction leads to hyperbranched products. This is due to the fact that M, which is for ordinary radical polymerizations a monofunctional monomer, becomes bifunctional in this special case of initiation.

On the other hand, if A is the water‐soluble polymer derived from M, one or more other monomers can be grafted onto the backbone of this polymer leading to graft‐blockcopolymers.
Ion binding in polyelectrolyte solutions. An account for noncoulombic interactions
Authors: Rebolj N. , Jamnik B. , Vlachy V.
Published: July 2012

Canonical Monte Carlo method is used to study a refined model of polyelectrolyte solution. The discrete charges on a polyion are located periodically along the helix. The ion‐ion and ion‐polyion interactions are described by a solvent‐averaged potential which accounts for the desolvation of ions. The major parameters of the short‐range potential function are Gurney coefficients for the counterion‐counterion (Acc) and the charged group‐counterion interaction (Apc). From simulations, the self‐diffusion coefficient for counterions, D/Do, was calculated. This quantity is rather sensitive to the value of Apc and much less to the choice of the counterion‐counterion coefficient. The refined model is used to analyze a fraction of apparently free counterions, α (≈D/D0), as obtained from recent measurements of transport properties in aqueous solutions of lithium and cesium poly(styrenesulfonate). The values of Gurney parameters, which fit experimental results, are determined: for a good agreement with experimental data an additional repulsive interaction Apc≈3900 J/mol is required for lithium poly(styrenesulfonate) at 5°C. This value is smaller (≈1500 J/mol) for lithium salt at 35°C, and negative, ≈−130 J/mol, for cesium salt of poly(styrenesulfonic) acid.
Counterion induced bundle formation of rodlike polyelectrolytes
Authors: Tang Jay X. , Wong Shuen , Tran Phong T. , Janmey Paul A.
Published: July 2012

A number of filamentous biopolymers including actin filaments (F‐actin), microtubules (MT), tobacco mosaic virus (TMV), and the filamentous bacteriophage fd form bundles under well‐defined conditions. All of these macromolecules are negatively charged rodlike assemblies, and lateral association is induced by a number of cations such as divalent and trivalent metal ions and homopolymers of basic peptides. The general features of bundle formation are largely independent of the specific structure of the biopolymers and the bundling agent used. They are also approximately independent of the concentration of macromolecules. However, a threshold concentration of bundling agent is required in order to form large lateral aggregates, detected by a sharp increase in light scattering and by electron microscopy. The threshold concentration varies strongly with the valence of the cations and increases with the ionic strength of the solution. The formation of bundles is reversible by polyanions such as nucleoside phosphates. This overall behavior is similar to the phenomenon of DNA condensation and can be explained by applying polyelectrolyte theories, including the concept of counterion condensation. Our results provide quantitative comparisons with a number of predictions of polyelectrolyte theories, including the calculation of apparent binding affinity and its dependence on ionic strength. They also support the prediction of an attractive interaction between the neighboring filaments due to sharing of counterion clouds. In addition, the simply detectable, reversible assembly of macromolecules in solution serves as a sensitive indicator of the active association of small ions and the formation of ion clusters. Association constants of Co(NH3)‐ATP and Lys18‐ATP were determined by application of this model.
Particularities in static and dynamic light scattering from branched polyelectrolytes in comparison to their linear analogues
Authors: Burchard Walther , Frank Markus , Michel Eduard
Published: July 2012

The expansion behaviour of branched strong polyelectrolytes when lowering the ionic strength was compared with the corresponding linear chains. Two pairs of polymers were chosen (a) linear poly(allylamine hydrochloride) with the corresponding intramolecularly crosslinked microgel and (b) cationic amylose derivatives with the corresponding derivative of potato starch that consists mainly of the branched amylopectin. The cationic group in the polysaccharides was a quaternized amine. As expected the expansion behaviour of the branched materials is considerably less than of the linear chains. Surprisingly the ratio of the radius of gyration to the hydrodynamic radius ρ=Rg/Rh showed opposite behaviour and increased for the linear chains (rod like behaviour) but decreased for the branched materials to sphere like behaviour when the ionic strength was lowered.

A more detailed analysis of the structure was possible with the polysaccharides. Because of their large dimensions the angular dependence of the scattered light could be measured. The data were analysed from Kratky plots. The branched amylopectin showed no change in the self‐similarity when the ionic strength was lowered and could be described by a fractal dimension of about df = 2.2. Very different behaviour was found with the amylose derivative. A rod‐like structure was obtained at high ionic strength that underwent a transition to a disordered conformation that however, is not that of a random coil. Various model calculation were made which give evidence for a folded double helix with loops in between. At low ionic strength the two double‐helix section unfold and the loop strongly expands.
Scattering properties of weakly charged polyelectrolytes
Authors: Borsali Redouane
Published: July 2012

The static properties of semi‐dilute polysaccharide salt‐free solutions as revealed by light scattering and small angle neutron scattering (SANS) are presented. As expected the results show the existence of a broad scattering intensity peak in the investigated range of polyelectrolyte concentration Cp and momentum transfer q in both light and SANS experiments. For all charge parameters, the positions of the peaks scale roughly as C0.5p. A new data treatment is proposed to analyze the effect of the polyelectrolyte concentration Cp and particularly the charge parameter λ. The results reveal, for the investigated domain of concentration, a strong evidence of the chain coiling as the charge parameter λ is decreased. This observation is valid for λ<1, i.e. above the Manning condensation limit. The case of polystyrene sulfonate is presented for comparison.
Long‐range electrostatic attraction between macroions mediated by oppositely charged counterions: Experimental supports, past and present
Authors: Ise Norio
Published: July 2012

Recent experimental observations are reviewed, which testify to the existence of electrostatic attraction between colloidal particles. The ultra‐small‐angle X‐ray scattering technique shows five orders of Bragg diffraction for colloidal silica particle dispersions, indicating that a (bcc) single crystal of a lattice constant of 3000 A is formed. The closest interparticle spacing can be accurately determined and is definitely smaller than the average spacing calculated from the particle concentration. This implies that contraction takes place during crystallization and the dispersion is no longer homogeneous but contains the single crystal, voids and/or free particles. Two types of symmetries, six‐fold and four‐fold, are observed from the same dispersion with {110} planes (most densely packed planes of the bcc structure) parallel to the capillary surface. This implies that the presumably negatively charged surface does not repel the anionic particles but actually attracts them. The void formation, which is a direct evidence of the attraction, is further confirmed for rather small latex particles under the density‐matched condition. Furthermore, the same latex particles are found to show the macroscopic vapor‐liquid condensation when the density difference between the particle and the medium is not adjusted. These two phenomena are thermodynamically the same. The results are analyzed in terms of the Sogami potential. The recent measurements of interparticle potential are critically reviewed. It is pointed out that only rather short distances are covered in the surface force measurements and the atomic force microscopy so that the long‐range attraction in question cannot be detected. A method based on the determination of the distribution function demonstrates the presence of a long‐range attraction in addition to the widely accepted repulsion, and the results are successfully reproduced by the Sogami potential. The positive adsorption of ionic entities near like‐charged interface is in direct contradiction to the standard double layer interaction theory and shows the presence of electrostatic attraction between the interface and particles. The attraction is generated through the intermediary of counterions present in the space between particles or between particles and plate. Considering the nature of the Sogami treatment, it is proposed to call the attraction the counterion‐mediated Gibbs attraction.
Static and dynamic light‐scattering of colloidal crystals of monodispersed polystyrene spheres
Authors: Okubo Tsuneo , Kiriyama Kohei
Published: July 2012

Static and dynamic light‐scattering measurements are made for colloidal‐crystals, ‐liquids and ‐gases of monodispersed polystyrene spheres, 109 nm in diameter, in the exhaustively, deionized suspension and in the presence of sodium chloride. Sharp peaks in the scattering curve are observed for the colloidal crystals in very diluted aqueous suspension. The product of the effective diffusion coefficient and the scattered light intensity is found constant over the whole range of the scattering angle measured for the colloidal crystals. Three and two dynamic processes have been extracted separately from time profiles of autocorrelation functions of colloidal crystals and liquids, respectively from the non‐negative least square analysis. Decay curves of colloidal gases are characterized by a single translational diffusion coefficient, D0. D0 of the gases at low ionic concentrations is lower than the calculation (Dc) from the Stokes‐Einstein equation with the true diameter of spheres, and increases and reaches Dc as ionic concentration increases. These experimental results emphasize the important role of the expanded electrical double layers on the diffusive properties in the colloidal crystals, liquids and gases.
Interaction of polyelectrolytes with mono‐ and divalent cations
Authors: Ludwig H. , Loebel K.‐H.
Published: July 2012

The counter ion condensation to the polyelectrolytes polyacrylate (PAA) and poly(maleate/acrylate)copolymer (MAC) was measured for Na+−, K+−, Ca2+−, Cd2+, and Cu2+−ions in aqueous solutions by means of ion‐selective electrodes. The competition between monovalent and divalent ions was investigated. From the studies an order of counter ion effectiveness was obtained: Na+ binds stronger than K+ and Cu2+ stronger than Cd2+ and these two much stronger than Ca2+.

The pressure dependence of Cd2+ condensation in competition to the large TRIS+ ions was determined in the pressure range from 0.1 to 500 MPa. The results indicate a volume increase of about 14ml/mol when Cd2+ is bound to the polyelectrolytes PAA or MAC. This leads to the conclusion that cadmium ions become dehydrated during the condensation process.
Marked discreteness on the coil‐globule transition of single duplex DNA
Authors: Yoshikawa K. , Kidoaki S. , Takahashi M. , Vasilevskaya V. V. , Khokhlov A. R.
Published: July 2012

From the study of single molecular observation of individual DNA chains by use of fluorescence microscopy, it has become clear that the transition between elongated coil state and compacted globule state is highly discrete on the level of individual chains. On the other hand, the transition appears continuous on the level of the ensemble of DNAs. We report the experimental evidence on this unique property of the DNA chain, using T4 DNA, 166 kilo base pairs (kbp), with the addition of Co(NH3)3+6. Theoretical consideration has been performed on the bimodality in the free energy of single DNA chains, indicating that the character of the coil‐globule transition changes largely depending on the valency of the coexistence cationic species.
Counterion condensation in xanthan aqueous solutions in the semidilute and concentrated regime
Authors: Bordi F. , Cametti C. , Paradossi G.
Published: July 2012

The dielectric and conductometric properties of aqueous solutions of Xanthan have been investigated from 1 kHz to 1 GHz by means of frequency domain dielectric spectroscopy, at different polyion concentrations from 0.5 to 10 mg/ml, covering both the semidilute and concentrated regimes. The dielectric spectra have been analysed, in these concentration regions, on the basis of a fixed counterion condensation model, considering that a fraction of counterions will remain in the neighbouring of each charged group of the polyion and that this fraction does not change with the degree of ionization and polymer concentration. This assumption, which differs from that given by the Manning model for charged polyelectrolyte solutions, defines the overall dielectric and conductivity behaviour of the system over the whole temperature interval and polymer concentration investigated.
Remarks on the forces between macroscopic particles in solution
Authors: Patey G. N.
Published: July 2012

Some interesting aspects of the forces acting between macroscopic objects (spheres and plates) immersed in solution are discussed. These include attractive forces between like‐charged objects in primitive model electrolyte solutions, van der Waals forces in molecular solvents, and strong attractive interactions related to cavitation or separation‐induced evaporation of liquids between inert or “solvophobic” walls.
The critical onset of counterion condensation: A survey of its experimental and theoretical basis
Authors: Manning Gerald S.
Published: July 2012

A survey of experimental and theoretical investigations into the condensation of counterions on polyelectrolyte chains above a critical threshold of polymer charge density is presented. Current models contain critical formation of a condensed layer‐that cannot be diluted off the polymer but differ qualitatively in their description of the structure of the layer. A documented position is taken that the model of a line of discrete charges is more realistic than a uniformly charged cylinder. The question of attractive electrostatic interactions between identically charged polymers is addressed.
Theoretical and experimental investigations of adsorbed protein structure at a fluid interface
Authors: Atkinson P. J. , Dickinson E. , Horne D. S. , Leermakers F. A. M. , Richardson R. M.
Published: July 2012

The structure of adsorbed layers of the disordered milk protein β‐casein at the air‐water interface determined by specular neutron reflectivity measurements is presented and compared with results obtained from self‐consistent‐field modelling of a β‐casein look‐alike molecule at a solid‐water interface. Changes in the layer structure with substrate pH in the range pH 5.5‐7.0 have been determined experimentally and have been estimated theoretically. At pH 7 the neutron reflectivity data are fitted using a two‐layer model of the adsorbed protein film consisting of a thin (≈Å) protein‐rich region (φ≈0.95) at the interface and a thicker (≈45 Å), more diffuse (φ≈0.15), layer extending into the bulk aqueous phase. On reducing the substrate pH towards the protein isoelectric point, a thickening of the adsorbed layer is observed which is attributed to secondary adsorption of protein parallel to the monolayer observed at pH 7. The thicknesses of both layers in the fitted model, and the volume fraction of protein in the diffuse layer, increase to accommodate the extra protein. A model, linear chain polyelectrolyte consisting of apolar, polar (uncharged) and polar (pH‐dependent charge) residues is constructed in a sequence which mirrors the known primary structure of β‐casein. The adsorption behaviour of this casein look‐alike at a solid‐water interface is modelled using the self‐consistent‐field theories of Scheutjens and Fleer, under similar conditions of pH as for the specular neutron reflection experiments. Total segment density profiles are obtained which show very good qualitative agreement with the experimental results. At neutral pH, the monolayer profile φ(z) falls off in a smooth fashion from very high values at the interface (φ≈0.95) to values close to the bulk concentration over about 50 Å. On reducing the pH, the adsorbed amount is seen to increase, with the additional material appearing as a shoulder on the φ(z) profile, as observed in the neutron experiments.
Competitive Reactions in Solutions of Protein‐Polyelectrolyte Complexes
Authors: Izumrudov Vladimir A.
Published: July 2012

The ability of negatively charged globular proteins (bovine serum albumin, trypsin soy inhibitor) to interact with linear synthetic polycations (poly‐N‐ethyl‐4‐vinylpyridinium bromide, poly‐N,N‐dimethyldiallylammonium chloride) and to form negatively charged water‐soluble complexes, in which the protein is a lyophilizing component has been revealed. The complexes are formed if the total number of the protein negative charges exceeds the total number of the polycation positive charges in the mixture. The composition of the complexes remains virtually unchanged and corresponds to one chain of polycation and only such number of protein globules that provides the solubility of the complex particle as a whole. The competitive reaction accompanied with transfer of the protein globule from one complex species to another one was studied by fluorescence quenching technique. It is shown that the rate of the reaction is quite high even in dilute aqueous solution and becomes higher after addition of salt (NaCl). As it follows from the results obtained these model systems obey the basic principles established for interpolyelectrolyte reactions in solutions of oppositely charged flexible‐chain synthetic polyions.
Surfactant binding to oppositely charged polyion
Authors: Bezan Marjan , Malavasic Mateja , Vesnaver Gorazd
Published: July 2012

Binding of undecyl‐, tridecyl‐, tetradecyl‐, and pentadecyl‐pyridinium cations to poly(styrenesulfonate) anion, PSS−, in aqueous 0. 01 and 0. 1 m NaBr has been investigated by means of potentiometry based on the surfactant cation‐selective membrane electrodes and flow microcalorimetry. It has been observed that the cations of each surfactant start binding strongly to PSS− polyion at a total surfactant concentration well below its critical micelle concentration, cmc. Above this low limiting concentration the measured exothermic enthalpies of binding, ΔHb, expressed per mole of the bound surfactant become independent of the surfactant concentration. They do, however, increase with the increasing length of the surfactant hydrocarbon chain. These observations are in close agreement with the results of earlier studies on similar systems according to which strong surfactant binding to the oppositely charged polyions results primarily from the aggregation of the hydrocarbon chains of the bound surfactant ions into small aggregates. Comparison of the measured ΔHb values with the corresponding, recently determined enthalpies of micellization, ΔHmic, shows that the ΔHb values are by about 9 kj/mole more exothermic than the ΔHmic values, regardless of the surfactant chain length or the simple salt concentration. This suggests that besides the micellization of the bound surfactant ions the polyion‐counterion‐solvent interactions taking place in the immediate vicinity of the polyion in a local environment that consists of surfactant hydrocarbon tails and water molecules may also play an important role in determining the binding of surfactant ions to the charged macromolecules.
Interactions of polyelectrolytes with the lyotropic liquid crystalline system na‐dodecylsulfate/decanol/water
Authors: Kosmella Sabine , Kötz Joachim , Friberg Stig E. , MacKay Raymond E.
Published: July 2012

The influence of a cationic charged polyelectrolyte, poly(diallyldimethylammonium chloride) on the interlayer spacing of the lamellar liquid crystalline system Na‐dodecylsulfate (SDS)/decanol/water was investigated by means of low‐angle X‐ray diffraction, polarized microscopy and rheology. It could be demonstrated that a lamellar liquid crystalline phase was still formed by introducing a cationic polymer of 5000g/mol into the mesophase, whereas different phenomena are observed in dependence on the polymer concentration. The average thickness of the layer, that means the layer repeat unit, is not influenced in the range of lower polymer concentration (up to 1%). At 2% polymer a lamellar liquid crystalline phase formed by SDS and decanol molecules and a “frozen” structure including polymer chains existing side by side. In a range of 5% and 10% polymer the “frozen” structure is the dominant one. It is assumed that electrostatic interactions determine the location of the polymer in the water layer between the surfactant head groups. Rheological investigations support the proposed model.
Light scattering experiments near the sol/gel transition temperature of thermo‐reversible gels formed by aqueous solutions of an arborol
Authors: Engelhardt Th.‐P. , Belkoura L. , Woermann D.
Published: July 2012

Molecules of the amphiphilic polyalcohol [9]‐10‐[9] arborol (molar mass M = 1053 g mol−1) dissolved in water form gels which are thermo‐reversible and shear sensitive. The gel formation sets in above a characteristic composition ygel of the solution and temperature Tgel (ygel = 7.5·10−3; Tgel≈35°C; y, mass fraction of the arborol). Tgel increases (slowly) with increasing values of y>ygel (Tgel(y = 0.02) ≈ 47°C). The “stiffness” of the gels increases with increasing values of y and increasing values of the temperature difference (Tgel−T). The states of the solutions (of the gels) at temperatures near Tgel and compositions near ygel are studied by static and dynamic light scattering experiments. The dynamics of the structure of dilute arborol gels at constant temperature allows to obtain the normalized ensemble averaged correlation function g(2)(q, τ) of the light scattered by the gels by accumulating the corresponding time averaged correlation function g2time(q, τ) over long times t up to 150 h (q, scattering vector; τ, correlation time). The kinetics of the aggregation and the gel formation after a temperature jump from an initial thermodynamic equilibrium state at temperature Ti (> Tgel) to a final temperature Tf (< Tgel) is monitored by static light scattering experiments. The change of the scattered intensity Is (θ = 90°) (θ, scattering angle) at Tf with time t shows two regimes: an “aggregation regime” (t<tgel;tgel, relation time; i. e. (Is‐IO)∼tz with z ≈ 0.66) and a “gelation regime” (t→tgel; i. e. (Is‐IO)∼[tgel‐t)/tgel]−y with y ≈ 1. 1). In both regimes the aggregation of large aggregates of the arborol molecules seems to be the dominant process. The gelation time of dilute gels is of the order of 10 h. It decreases with increasing concentration of arborol.
Synthesis and characterization of polyampholyte hydrogels
Authors: Kudaibergenov Sarkyt E.
Published: July 2012

Several types of water‐swelling polyampholyte gels have been synthesized by gamma‐irradiation copolymerization and the behaviour of crosslinked amphoteric macromolecules was studied in dependence of pH, ionic strength and DC electric field. It has been shown that both polyampholyte gels and interpenetrating polyelectrolyte networks swell near of the isoelectric points. Under the action of DC electric field polyampholyte gels are able to produce an eel‐like motion.
Structure and function of phenolsulfonic acid/formaldehyde ion exchange gels
Authors: Schink J. , Belkoura L. , Woermann D. , Yeh F. , Li Y. J. , Chu B.
Published: July 2012

Phenolsulfonic acid/formaldehyde ion exchange membranes exhibit unexpected transport properties which deviate from that predicted by the standard model of transport across ion exchange membranes. Small‐angle X‐ray scattering experiments (0.118 nm−1 < q < 0.995 nm−1) and ultrasmall‐angle X‐ray scattering experiments (0.015 nm−1 < q < 0.05 nm−1) are carried out with two types of these gels to study their structure. The scattering patterns reveal inhomogeneities characterized by two lengths ζ1, and ζ2 with values of the order of ζ1 ≈︁ 1 nm and ζ2 ≈︁ 50 nm. On the basis of this finding a model for the structure of the gels is proposed which rationalizes qualitatively their observed transport properties.
Generation of noncentrosymmetric structures in glassy liquid crystalline siloxanes
Authors: Dietrich R. , Kastenmüller G. , Bourhill G. , Bräuchle G , Leigeber H. , Weitzel H. P. , Kreuzer F. H.
Published: July 2012

Photoisomerization has been used to induce polar order in azo‐dye‐containing polymeric liquid crystalline oligosiloxanes at room temperature. The extent of the induced polar order was probed using a Maker fringe analysis at 1064 and 1542 nm. All samples studied at 1064 nm gave asymmetric fringe maxima, which was ascribed to a gradient in the induced polar order. The benefits of this poling mechanism, which operates on the combined effect of both light and static electric fields, was highlighted via poling of a defined area of the liquid crystal. This ability to selectively write polar structures into the liquid crystals may lead to electro‐optic diffractive devices.
The conductance of the deionized colloidal dispersions
Authors: Sumaru Kimio , Yamaoka Hitoshi , Ito Kensaku
Published: July 2012

The conductance of deionized and protonated styrene‐styrenesulfonate copolymer dispersions of various particle sizes and charge numbers were measured, and the conductometric coefficient (f) was defined as the ratio of the practical conductance to the one calculated simply from the total concentration of protons. The experimental values were compared with the theoretical ones obtained by modifying the formulation in the Ohshima‐Healy‐White theory, which was originally established for salt‐added systems. Although the theoretical values turned to be slightly smaller than the experimental data, they reproduced the experimental tendency to a certain extent. Furthermore the added [HC1] and [NaCl] dependence of the conductance was also evaluated for deionized and protonated samples, and additivity of conductivity was discussed.
Relaxation of highly vibrationally excited cycloheptatriene in gases at high densities and in liquids
Authors: Benzler J. , Linkersdörfer S. , Luther K.
Published: July 2012

Vibrational relaxation of highly excited ground state 1,3,5‐Cycloheptatriene (CHT) has been investigated by picosecond transient absorption spectroscopy in gases (nitrogen and ethane) at pressures up to 200 bar and in the liquid solvents ethane, heptane, C2Cl3F3 and methanol. The results show that in the gas phase, the relaxation rates are proportional to the bath gas density within the studied pressure range. In contrast, the relaxation in liquids is significantly slower than predicted by common models for the collision frequency at high densities.
Enrichment of Na and K or 6Li and 7Li by counter current flow of the coexisting phases of Na/K‐ or 6Li/7Li‐ammonia solutions
Authors: Schindewolf U. , Reheis Th.
Published: July 2012

Metal‐ammonia solutions (M‐AS) have a miscibility gap, they separate at low temperatures into a diluted, electrolytic phase of high density and a concentrated, metallic phase of low density. In mixed sodium‐potassium solutions (Na/K‐AS) after phase separation sodium is enriched in the metallic phase, the separation factor αNa/K (Eq. (2)) is the larger, the lower the temperature relative to the critical temperature of the miscibility gap or the wider the miscibility gap. Therefore in deuteroammonia solutions (DAS) with higher critical temperatures the enrichment is more effective than in normal ammonia solutions. In Li‐DAS with the two stable isotopes 6Li and 7Li the lighter one is enriched in the metallic phase. The separation factor (Eq. (4)) is αLi ≈ 1.010 at −73°C. By multiplication of the single equilibrium effect in a counter current column, which acts like a solvent‐solvent extraction column, the species can be enriched. The counter current operation of the column was enforced by electrochemical means (application of a dc‐current through the column), and the enrichment was tested around −74°C with equimolar Na/K‐AS and Na/K‐DAS for which αNa/K = 1.61 and 1.70 resp. and with Li‐DAS of natural Li‐isotope abundance. The height of the theoretical plate of the column for all three systems was HTP = 12.9±0.3 cm.
Density equilibration in a near‐critical fluid under reduced gravity
Authors: Ikier C. , Klein H. , Woermann D.
Published: July 2012

A quick response of laser beam attenuation is found when a temperature change is imposed on near‐critical SF6 at reduced gravity in space (“piston effect”). The time to reach thermodynamic equilibrium is not correspondingly short. Density equilibration is a long lasting slow process. The times of density equilibration suggest a scaling with the temperature difference (T‐Tc).
The role of solvent structure in perturbation methods applied to the dissolution of an apolar solute in water
Authors: Re Mario , Laria Daniel , Fernández‐Prini Roberto
Published: July 2012

In view of recent experimental and simulation studies which show that solvent reorientation does not play a significant role in the dissolution of small apolar solutes in water, the performance of first order perturbation theories (FOPT) has been reassessed.

A contribution which cannot be obtained from classical FOPT is the many‐body effect of the instantaneous solvent electric field which induces a dipole on the apolar solute and contributes an attractive term. The average square electric field was determined by molecular dynamics for solutes of different size and its effect upon the solute's chemical potential was calculated from it with an appropriate extension of the test‐particle method. The contribution of this term to the thermodynamic quantities of dissolution is discussed.
Bond angle distribution in amorphous germania and silica
Authors: Neuefeind Jörg , Liss K.‐D.
Published: July 2012

The distribution of Ge‐O‐Ge and Si‐O‐Si bond angles α in amorphous germania and silica is re‐determined on the basis of diffraction experiments. The bond angle α joining adjacent tetrahedra is the central parameter of any continuous random network description (CRN) of these glasses. New high energy photon diffraction experiments on amorphous germania (at photon energies of 97 and 149 keV) are presented, covering the momentum transfer 0.6–33.5 Å−1. In photon diffraction experiments on GeO2 the contribution of the OO pairs is very small. To obtain a similar information for amorphous SiO2, high energy photon diffraction experiments [1] have been combined with neutron diffraction data [2, 3] on amorphous silica in order to eliminate the OO‐partial structure factor. With this technique it is shown that the Si‐O‐Si angle distribution is fairly narrow (σ = 7.5°) and in fact comparable in width to the Ge‐O‐Ge angle distribution (σ = 8.3°), a result which differs from current opinion. The narrower distribution found in this study are in much better agreement to the determinations based on 29Si‐MAS‐NMR. Among the various models relating the chemical shift to the bond angle, best agreement is found with those models based on the secant model. Sharp components in the bond angle distribution can be excluded within the reached real space resolution of 0.09 Å.
Determination of vapour‐liquid equilibria of two‐centre Lennard‐Jones fluids in the canonical ensemble
Authors: Kristóf Tamás , Liszi János , Szalai István
Published: July 2012

Vapour‐liquid equilibrium data were determined for a two‐centre Lennard‐Jones fluid with reduced bond length L* = 0.505. The method used is based on the Taylor expansions of both the chemical potential and the pressure calculated by Monte Carlo simulation in the canonical ensemble. New phase coexistence data were obtained at rather low temperatures applying an independent simulation method for the calculation of the chemical potential. Thermodynamic consistency of the vapour pressures as well as the saturated vapour and liquid densities was confirmed on the basis of the Clausius‐Clapeyron equation.
Structural relaxation of glass‐formers confined to sol‐gel‐type porous glasses
Authors: Yan X. , Streck C. , Richert R.
Published: July 2012

We combine the results of dielectric relaxation spectroscopy and solvation dynamics measurements for the glass‐forming liquid 2‐methyltetrahydrofuran spatially confined to the pores of sol‐gel glasses with pore diameters ϕ = 2.5, 5.0, and 7.5 nm. Although both techniques probe the orientational polarization of the polar liquid, a dielectric experiment is bound to sense macroscopic effects, whereas the solvation method probes the molecular dynamics on microscopic scales. When the temperature approaches the glass‐transition at Tg upon cooling, an interfacial liquid layer with strongly frustrated dynamics grows in thickness and is thus able to block the connectivity among the pores. As a result the structural α‐process is subject to an enhanced spatial restriction near Tg and a transition from constant pressure to constant volume conditions might occur as the pore connectivity becomes obstructed by immobile liquid.
Investigating the cooling rate dependence of amorphous silica: A computer simulation study
Authors: Vollmayr K. , Kob W.
Published: July 2012

We use molecular dynamics computer simulations to study the dependence of the properties of amorphous silica on the cooling rate with which the glass has been produced. In particular we show that the density, the glass transition temperature, the radial distribution function and the distribution of the size of the rings depend on the cooling rate.
Surface induced devitrification of glasses: The influence of elastic strains
Authors: Schmelzer J. , Gutzow I. , Möller J. , Pascova R.
Published: July 2012

It is shown that the account of elastic strains evolving in crystallization processes of glasses may be of significant importance for the understanding of the often observed preferential surface devitrification of a variety of vitreous materials. According to the discussed here mechanism the only parameter of the considered system determining the preference to surface crystallization is the misfit parameter δ. δ is a measure of the relative change of the volume of the glass in crystallization. In agreement with experimental results it is found that preferential surface crystallization has to be expected to occur for systems with large values of the misfit parameter δ. Moreover, in comparison with planar interfaces, the inhibiting effect of elastic strains on crystallization is even more decreased for glass powders and rough surface structures of the glass samples. In this way, powders of glass, edges, corners etc. on the glass surface may serve as centers for crystallization.
Application of borophosphosilicate glass (BPSG) in microelectronic processing
Authors: Kirchhoff M. , Ilg M. , Cote D.
Published: July 2012

In semiconductor industry borophosphosilicate glass (BPSG) films formed by chemical vapor deposition (CVD) are widely utilized as dielectric layers between conductor lines. This glass has to provide void‐free fill of 0.2–0.5 μm wide spaces between conducting lines with aspect ratios up to 4:1. Therefore good glass reflow properties, which are a function of boron and phosphorus dopant concentration and of deposition and anneal temperature, are required. Dopant concentrations need to be low enough to avoid undesired surface crystallization phenomena and to provide a stable surface. Anneal temperatures have to be low to fulfill the thermal budget criteria of advanced silicon devices.
Rheological behaviour of textured glass‐ceramic melts produced by the cylinder compression method
Authors: Deubener J. , Brückner R.
Published: July 2012

The rheological behaviour of glass‐ceramic Li‐disilicate melts is characterized by the Newtonian and non‐Newtonian viscosity. These quantities are determined from the thermally corrected rate‐dependent flow curves of the cylinder compression experiments on the basis of equal (Newtonian) equilibrium viscosities (isochomal conditions). Certain crystalline volume fractions in the glass samples are produced by primary nucleation and crystallization treatments.

The flow parameters show a characteristic non‐linear decrease with increasing compression rates. This two step shear thinning behaviour is determined, within the range of small deformation rates, by the suspension effect of the initial crystals and at larger deformation rates by the non‐Newtonian flow behaviour of glass melt matrix. The suspension effect is based on a flow orientation mechanism of the crystals, building up a certain texture. The alignment depends on the size, shape and concentration of the specimens. Based on a recently developed flow equation for stress induced changes of viscosity in single‐phase glass melts, a qualitative and quantitative description of the non‐Newtonian flow behaviour of glass melts with suspended crystals is presented.
Influence of pressure and shear flow on the crystallization behaviour of a glass melt based on the Li2Si2O5‐composition
Authors: Durschang B. R. , Carl G. , Rüssel C. , Gutzow I.
Published: July 2012

Extrusion experiments of a glass melt, based on lithiumdisilicate, show a different crystallization behaviour in comparison with experiments, where the same glass is heat treated identically, but without the pressure and the shear flow. Therefore, the effect of pressure and shear flow on the nucleation and crystal growth are discussed. It is shown theoretically and practically that at least for the lithiumdisilicate the pressure used is not sufficient to reach significant differences in crystallization. The shear flow is supposed to cause the crystallization catalysis due to the non‐Newtonian flow behaviour of the glass melt used.
In situ electrochemical and spectrophotometric investigation of the oxygen pressure dependence of the [Cr(VI)]/[Cr(III)] ratio in a borosilicate melt
Authors: Claes P. , Duveiller Ph. , Tilquin J.‐Y. , Glibert J.
Published: July 2012

The ratio R = [Cr(VI)]/[Cr(III)] has been measured in a Na2O·1.2SiO2·1.2B2O3 melt at 1000°C by spectrophotometry and by electrochemistry as a function of the partial pressure of oxygen in the gaseous atmosphere above the melt. Spectrochemical and electrochemical determinations are in quite good agreement and fit the linear relationship between log R and logP(O2) which is predicted by a thermodynamic development. This double agreement gives a good degree of confidence to in situ high temperature electrochemical measurements in oxide melts.
Problems of the voltammetric on‐line determination of iron and sulfur in industrial glass melts
Authors: Müller‐Simon H. , Szafarczyk M.
Published: July 2012

For some years efforts have been made in order to utilize voltammetric methods for glass technology. Different boundary conditions and the specific use as an analytical tool lead to some particular requirements in industrial application.

For industrial use the electronic equipment has to be protected against electronic perturbation due to electric boosting. In order to shelter the control devices against dust and heat, these devices must be installed at quite a distance from the investigated glass melt, which gives rise to disturbances in the measured voltammograms. The most important problem is the fixing of the area of the measuring electrode, which varies due to glass level variations.

The identification of the different influences and some solutions will be presented. In order to take also the influence of different glass compositions into account, the measuring setup should be calibrated for each particular glass melt. If all influences on the measured signal are known, a single point will be sufficient in order to calibrate the system.
About electrochemical reactions between a BaO‐ and a PbO‐Rich melt, short‐circuited by platinum
Authors: Kaps Ch.
Published: July 2012

The “Reboilling” effect is well known. If glass fragments with very different alkali oxide contents are remelted together in a platinum crucible, there can take place a local generation of gas bubbles. Similar effects were observed in a study of the Ba/Pb interdiffusion kinetics between two melts with the same molar composition (MO)33.3(B2O3)66.7‐s(EO2)s (M = Ba and Pb, resp.; E = Ge, s = 0.15 and Si, s = 0.10, resp.). The thermodynamic potential of the melts and the electrochemical mobilities of the ions Ba2+ and Pb2+ will be discussed in connection with the above described phenomenon. At 700°C the Ba/Pb ion‐exchange in the ratio 1/1 shows a dominant viscosity‐controlling. The formation of gas bubbles is caused by reactions, influenced by the experimental arrangement and by the melt compositions.
Kinetics of glass corrosion in acid solutions
Authors: Helebrant Aleš , Pekárková Iveta
Published: July 2012

The interaction of simulated nuclear waste borosilicate glass with acid solutions (pH = 2, pH = 4) was studied under static conditions (i.e. without refreshment of corroding solution) at 30, 60 and 90°C. Tests with stirred and unstirred solution were compared. The rate of glass dissolution (given by the rate of SiO2 transfer into the solution) and the rate of glass leaching (represented by the rate of sodium transfer into the solution) were significantly higher at lower pH and in stirred solution. The first phenomenon can be explained by the more extensive opening of glass structure at lower pH. The second phenomenon can be caused by the creation of thin solution layer adjacent to the glass surface in the case of unstirred corroding media. The SiO2 and sodium concentration in this layer are then higher in comparison to the bulk solution. Due to this fact the driving force of glass matrix dissolution and sodium leaching are lower than in the case of stirred solution. The temperature dependencies of the initial rate of glass matrix dissolution and of the sodium diffusion coefficient can be described using equations of Arrhenius' type.
Investigation of the flaws of container glass introduced by aluminium on the recycled glass cullets by means of ir and raman microspectroscopy
Authors: Meyer K. , Traufelder S. , Stachel D.
Published: July 2012

The introduction of aluminium contained in the recycled glass cullets into the melts of container glass results in the formation of silicon spheres as a well known glass flaw. Besides the glasses of our test melts are inhomogeneous and coloured brown, dark brown, and grey around these silicon spheres. The different coloured regions are investigated by mapping the glass sample using IR and Raman microspectroscopy to find out the nature of the inhomogeneities. Only in the brown regions silicon could be detected. Therefore the brown colour should be caused by silicon particles. The grey regions of the glass contain Al2O3.
Ionic conduction in glass ceramics
Authors: Runge Andreas , Kahnt Hanno
Published: July 2012

The ionic conductivity in glass ceramics depends not only on the partial conductivities of the different phases and their volume fractions but — to large extend — on the structure of the composite material. Moreover, conductivity can be drastically increased by enhancement of ionic mobility along grain boundaries. The conductivity of glass ceramics is discussed in terms of upper and lower bounds depending on the degree of information about the structure. An effective medium approach is used to describe the dc conductivity for some characteristic types of structure. This approach is extended to the frequency dependence of conductivity. The model is applied to experimental data from glass ceramics of the system SiO2‐PbO‐PbF2. In this system different structures have been realized leading to an increase or decrease of conductivity by up to three orders of magnitude compared to the starting glass.