bluuebunny/crossref_metadata_2025 huggingface dataset:
A direct measurement of the reaction NH3 + NH→2NH2
Authors: Röhrig M. , Römming H.‐J. , Wagner H. Gg.
Published: July 2012

The reaction of NH in its electronic ground state with ammonia was investigated behind incident shock waves using narrow line width absorption detection of NH(X3Σ−). The initial concentrations of HN3 which was used as source of NH(X3Σ−) were very low in order to reduce the influence of secondary reactions. Thus it became possible to measure kinetic data for the reaction of NH(X3Σ−) + NH3 (1) directly. In a temperature range from 1300 to 1700 K a rate constant k1 = 10(14.5±0.3)exp (–(112±9)kJ mol−1/RT)cm3/mol s was obtained. The apparent energy of activation fits well into an Evans Polanyi plot for H abstraction reactions of NH(X3Σ−).
Die physikalische Chemie fester Stoffe
Authors: Schmalzried Hermann
Published: July 2012

Structure and activity of solids and their physico‐chemical interpretation are the subject matter of this overview. After sketching briefly the history of the development of the physical chemistry of solids, solid state kinetics in particular is treated here. Examples are given which show how physico‐chemical concepts influence technologies that are responsible for many aspects of modern civilization. We discuss in particular (1) Point defect thermodynamics and point defect kinetics as the basis of amplifying devices. (2) Diffusional transport in crystals as the basis of solid state reactions and the formation of modern materials and tools. (3) The influence of the elastic potential on solid state kinetics and (4) Morphological stability and its influence on the course of solid state reactions.
Electrochemical reduction of CO2 at an activated silver electrode
Authors: Kostecki R. , Augustynski J.
Published: July 2012

The electrochemical reduction of CO2 to CO in aqueous NaClO4 solution saturated with CO2, at polycrystalline Ag cathodes was investigated as a function of the potential, temperature and electrolysis duration. A poisoning process has been found to occur in parallel with the CO formation. Building‐up of the surface species closely similar to the detected poison has been observed at a Ag electrode immersed (at open‐circuit) in a solution containing small amounts (10−4mol dm−3) of formaldehyde. A periodic anodic stripping of these inhibiting species was shown to produce stable current densities and faradaic efficiencies of CO over 4 – 5 h electrolysis runs. A tentative reaction pathway for CO2 reduction to CO, taking into account the experimentally determined onset potential, is proposed.
Transport coefficients and apparent charges of concentrated electrolyte solutions – Equations for practical use
Authors: Chhih Aziza , Turq Pierre , Bernard Olivier , Barthel Josef M. G. , Blum Lesser
Published: July 2012

Simple expressions for the transport coefficient in the mean spherical approximation (MSA) have been derived. We study the self‐diffusion, conductance and apparent charge of simple electrolytes, where we find good agreement for the concentration dependence. Associated electrolytes are also well described by a natural extension of this theory. The MSA equations extend the concentration range of the chemical model (CM) calculations which, in turn, are a reliable source for the input parameters of the MSA calculations.
The T,x,p‐phase diagram of binary phospholipid mixtures
Authors: Landwehr A. , Winter R.
Published: July 2012

High pressure differential thermal analysis (DTA) has been applied to the study of the temperature‐composition‐pressure phase diagram of the binary saturated phospholipid mixtures dimyristoyl/palmitoyl phosphatidylcholine (DMPC/DPPC) and dimyristoyl/stearoyl phosphatidylcholine (DMPC/DPPC) in excess water. A temperature range from 10 to 100°C and a pressure range from ambient up to 1500 bar has been covered. The experimentally obtained phase equilibria of these binary systems are compared with thermodynamic calculations for ideal and non‐ideal mixing behaviour, and with recent results from Monte Carlo computer simulation studies, which not only permit determination of the phase diagram but also reveal a pictorial view of the local structure of the mixtures in the different parts of the phase diagrams.
Au‐induced decomposition of N2O
Authors: Dietrich G. , Lützenkirchen K. , Becker St. , Hasse H.‐U. , Kluge H.‐J. , Lindinger M. , Schweikhard L. , Ziegler J. , Kuznetsov S.
Published: July 2012

Reactions between small gold cluster ions, Au, and N2O were studied in a Penning trap mass spectrometer. Gold clusters were produced by laser vaporization and injected into a Penning trap. After reaction times of 50–7000ms the products were detected by time‐of‐flight mass spectrometry. For the major reaction channel, Au + N2O→Au1,2N + NO+, rates of (0.9±0.1)×10−12 cm3 s−1 and (2.4±0.4)×10−12 cm3 s−1 were determined which are about a factor 500 below the collision rate. The corresponding activation energies for N2O decomposition were estimated to lie below 0.6 eV and 0.3 eV. Additional products with small branching ratios were detected, viz. the ions Au1O+, Au1N2O+, Au2N+, Au2NO+, Au2N2O+, Au3O+, Au3N2O+, and Au4N2O+. This indicates a preference for nitrogen‐oxygen bond rupture in the case of Au and Au, and for nitrogen‐nitrogen bond rupture in the case of Au.
Dipole‐bound electron states in HCN gas
Authors: Klahn Th. , Krebs P.
Published: July 2012

We have measured for the first time the drift mobility μ of electrons in HCN gas in the number density range 2.96×1017 ≤ n ≤ 3.60×1018 cm−3 at T = 294 K. The strong density dependence of the density‐normalized mobility (μn) of electrons at these low densities which has never been observed in less polar gases cannot be explained by multiple scattering effects. Assuming a dynamical electron attachment/detachment equilibrium involving the dipole‐bound electron state we can describe this anomalous density dependence. The striking density dependence of the mobility of anions observed for n≥ 1.98×1018 cm−3 is briefly discussed.
Instability of Moving Interfaces between Ionic Crystals KCl/AgCl
Authors: Schimschal‐Thölke S. , Schmalzried H. , Martin M.
Published: July 2012

The morphological evolution of initially planar phase boundaries between ionic crystals due to ion fluxes which are driven by an externally applied electric field is investigated. In this particular study, the boundaries under investigation are interfaces between KC1 and AgCl. It is shown that the moving boundary is morphologically unstable if the flux of silver ions is directed towards the KCl‐crystal, whereas it is stable if the flux of potassium ions is driven towards AgCl. This behaviour can be explained by the rules which derive from a formal stability analysis. The geometrical evolution of the moving phase boundary in its later stages is mainly governed by the elastic properties of the contiguous phases.
Diffusion Coefficients and Thermal Diffusion Factors for He–CO2, He–N2O and He–COS
Authors: Dunlop Peter J. , Bignell C. M.
Published: July 2012

The temperature dependence of diffusion coefficients and thermal diffusion factors at 300 K have been measured for the systems He–CO2, He–N2O and He–COS.
Electronic Energy Distribution in SrF by Investigation of the Molecular Chemiluminescence SrF(A2II1/2,3,2B2Σ+ → X2Σ+) and the Atomic Resonance Fluorescence Sr(53P1‐51S0) in the Time‐Domain following the Pulsed Dye Laser Generation of Sr(53PJ) in the presence of CH3F
Authors: Antrobus Stephen , Carl Shaun A. , Husain David , Lei Jie , Castaño Fernando , Sanchez Rayo Maria N.
Published: July 2012

A kinetic study is presented of the electronic energy distribution in SrF following the reaction of the electronically excited strontium atom, Sr(5s5p(3Pj)), 1.807 eV above its 5s2(1S0) electronic ground state, with CH3F. This optically metastable atom was generated by pulsed dye‐laser excitation of ground state strontium vapour to the Sr(53P1) state at λ = 689.3 nm (Sr(53P1←51S0)) at elevated temperature (850 K) in the presence of excess helium buffer gas in a slow flow system, kinetically equivalent to a static system. The decay of Sr(53PJ) was then monitored by time‐resolved atomic fluorescence from Sr(53P1) at the resonance wavelength following rapid Boltzmann equilibration within the 3PJ spin‐orbit manifold. Electronically excited SrF resulting from reaction of the excited atom with CH3F was also recorded in the time‐domain via the systems SrF(A2→1/2ΣX2Σ+) (νv = 0, λ = 662 nm), SrF(A2×3/2ΔX2Σ+) (ν = 0, λ = 652 nm) and SrF(B2Σ+X2Σ+) (νv = 0, λ = 579 nm). The A2 (181.9 kJ mol−1) and B2Σ+ (206.6 kJ mol−1) states of SrF are both energetically accessible on collision between Sr(3P) and CH3F. Both the atomic and molecular (A,B‐X) chemiluminescence emissions are shown to be exponential in form and characterised by first‐order decay coefficients which are found to be equal under identical conditions within experimental error. SrF(A2) and SrF(B2Σ+) are thus both shown to arise from direct reaction with CH3F. Further, the combination of integrated atomic and molecular intensity measurements, coupled with optical sensitivity calibration, enables estimates of the branching ratios into the A1/2,3/2, B and X states arising from Sr(53PJ) + CH3F to be made yielding the following results: A1/2, 6.4 × 10−3; A3/2, 1.5×10−3; B, 1.1x10−4; X, 0.992. The results obtained here are compared with analogous chemiluminescence studies on Sr(3P) with other halides obtained from molecular beam measurements and with previous kinetic measurements on SrCl, Br(A2, B2 + ‐X2Σ+) that we have reported. The results are also compared with those from a series of investigations we have presented from time‐domain investigations of molecular emissions from CaF, Cl, Br, I (A,B‐X) arising from the collisions of Ca(43PJ) with appropriate halides.
Electroosmotic and Hydrodynamic Oscillations in the Teorell Membrane System
Authors: Drouin Herbert R. L.
Published: July 2012

A system of two time‐dependent, first order differential equations of electrical membrane resistance and of hydrostatic pressure is derived. The equations are based on a set of flux equations for a 1,–1 valent electrolyte, combined with the equation of continuity, and the condition for conservation of mass. New insight into the functioning of the membrane oscillator is gained by the strict derivation of the relaxation equation of the averaged salt concentration with convection from the general partial differential equation. This relaxation equation is successfully transformed into the useful time‐dependent first order differential equation of the function of the electrical membrane resistance. Thereby the postulated relation for the concomitant changes of the electrical membrane resistance and the averaged salt concentration in the membrane phase is employed. The equations describe both the stationary and the non‐stationary states of Teorell's membrane oscillator. Particularly, the stationary pressure‐dependent, non‐monotonous current‐voltage curves and the current‐dependent, non‐monotonous pressure‐volume flux relations are calculated. These characteristics form the basis for mechano‐electrical transduction. Furthermore, the relaxation oscillations of membrane voltage, volume flux and hydrostatic pressure and the corresponding electroosmotic and hydrodynamic phase planes, representing stable limit cycles, are described. The stability criteria of the time‐dependent states are discussed.
Photoisomerization of Asymmetric Indobenzimidazolo Cyanine Dyes
Authors: Tatikolov Aleksandr S. , Derevyanko Nadezhda A. , Ishchenko Aleksandr A. , Baraldi Ivan , Caselli Monica , Momicchioli Fabio , Ponterini Glauco
Published: July 2012

The isomerization kinetics of three indobenzimidazolo polymethine cyanines have been investigated and compared with the corresponding properties of the parent symmetric dyes. A significant alternation of the π bond orders in the polymethine chain was found in the ground states (S0) of the asymmetric dyes. A similarly alternant behaviour was exhibited by the calculated S0 potential energy barriers for twisting around the polymethine chain bonds of the asymmetric carbocyanine, whereas uniform barriers were found for the symmetric parent compounds. The experimentally observed sequence of back‐isomerization activation energies was interpreted on the basis of these theoretical results. It was suggested by some spectral and kinetic fluorescence properties, and it was confirmed by the calculated polymethine‐chain π bond orders of the lowest singlet excited states (S1) that the electronic asymmetry induced by the different terminal heterocycles was strongly reduced upon excitation of these dyes to their S1 states. In spite of this, the trans‐cis photoisomerization of asymmetric cyanines occurred invariably around those bonds having the highest π bond orders in the ground state. A tentative theoretical explanation of this systematic behaviour is reported.
Recombination and Decomposition of Methylene Radicals at high Temperatures
Authors: Bauerle S. , Klatt M. , Wagner H. G. G.
Published: July 2012

Recombination and decomposition of methylene radicals have been investigated over a wide range of experimental conditions. It has been found that H atom forming channels play only a minor role in the reactions investigated. The rate constants for the recombination channels CH2+CH2°C2H2+H2 (1a) and C2H2+2H (1b) have been determined to be

k1a = 1015.2·.0.2Σ2·exp(‐(50±5) kJ mol−1/RT) cm3 mol−1 s−1

k1b = 1014.3±0.2·exp(‐(46±5) kJ mol−1/RT) cm3 mol−1 s−l

in the temperature range from 1100–2700 K.

The H atom channel in the decomposition of methylene in argon leading to CH+H (2 b) has been found to be

k2b = 1015.75±0.15·exp((‐375±15) kJ mol−1/RT) cm3 mol−1 s−l

at temperatures between 1900–2700K. A comparison with literature data available for channel (2a) leading to C+H2 shows that the contribution of the H atom channel (2b) in the decomposition reaction of CH2 is around 10–15%. The energy of activation is in good agreement with the theoretically calculated value.
Aggregation of Pseudoisocyanine Chloride in Aqueous Solutions at High Pressures
Authors: Neumann B. , Pollmann P.
Published: July 2012

The aggregation behavior of pseudoisocyanine chloride (= PIC) (1,1′‐diethyl‐2,2′‐cyanine chloride) in dilute aqueous solutions was observed up to 375 MPa by absorption spectroscopy. From the pressure dependence of the dimerization constant the change in volume associated with the dimerization, Δ VD = −12.6 cm3·mole−1, could be obtained. By means of this value of ΔVD the interplanar spacing of the quinoline rings in the dimer was estimated to 3.0·10−8 cm. At higher concentrations the pressure dependence of the pressure‐induced absorption‐band (Scheibeband) yields the volume contraction (Δ VS) caused by the aggregation. Evaluation of Δ VS/ Δ VD allows a rough determination of the mean aggregation number n of monomer units per Scheibe‐aggregate. n increases with increasing concentration of PIC. The values of n lie between 5 to 29.
Monolayers of Multichain Molecules: A Monte Carlo Study
Authors: Stettin H. , Schweigert T. , Wahab M. , Mögel H. J.
Published: July 2012

The aim of this work is to understand how the chain orientational order in monolayers depends on intramolecular connectivity. Therefore monolayers of one‐, two‐, three‐, and four‐chain flexible molecules have been simulated using the Monte Carlo technique. The chains are linked up in the head group region. Three‐ and four‐chain molecules can have both: linear rigid as well as flexible head groups. The simulations were carried out within a lattice model on the simple cubic lattice. Only the excluded volume effect was taken into account. For the calculation of the orientational order we used end‐end vectors of each chain in the molecule and vectors pointing from the centre of mass of the whole molecule to the centre of mass of the head group. If the chains in the molecules have equal lengths the degree of order calculated from end‐end vectors is neither influenced by connectivity in the head group region nor by the flexibility of the head group. The degree of order based on the centre of mass vectors clearly indicates an effect of the intramolecular connectivity and for short chains also an influence of the flexibility of the head groups.
A Novel Concept for Modeling the Time‐Temperature Dependence of Polar Order Relaxation in Nonlinear Optical Active Polymers
Authors: Winkelhahn H.‐J. , Servay Th. K. , Neher D.
Published: July 2012

The widely accepted concept of introducing a fictive temperature (Tf) to describe the structural relaxation below the glass transition temperature is transposed to explain the orientational dynamics of nonlinear optical (NLO) active chromophores in poled polymer systems. The influence of different thermal histories on the results of differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC) gives evidence for a direct connection between the structural relaxation as measured by DSC and the relaxation of polar order as measured by TSDC. With the fictive temperature being determined from the DSC experiments it is possible to relate the equilibrium dynamics of the NLO chromophores above the glass transition temperature as determined by dielectric spectroscopy to the nonequilibrium relaxation times of polar order relaxation below Tg over 12 decades in time. The obtained time‐temperature dependence for the relaxation times, based on Scherer's extension of the Adam‐Gibbs theory (AGV), shows a Vogel‐Fulcher behavior above Tg and an Arrhenius‐like behavior far below Tg. Below Tg the temperature dependence of the relaxation times of polar order is in excellent agreement with an empirically found modified Vogel‐Fulcher equation, which modeled the relaxation of polar order of different poled polymer systems in an universal manner. The AGV theory further offers a direct approach to introduce the influence of the thermal history on the time‐temperature characteristics of polar order relaxation.
Tris‐2,2′‐Bipyridylruthenium(II) Peroxydisulphate as a Photosensitizer in the Oxidative Degradation of 4‐Chlorophenol
Authors: Silva M. I. , Burrows H. D. , Miguel M. Graça , Formosinho S. J.
Published: July 2012

The photolysis of aerated aqueous solutions of 4‐chlorophenol in the presence of Ru(bpy)2+3 and peroxydisulphate has been followed by UV/visible absorption spectroscopy, and reveals a relatively rapid oxidative decomposition of the phenol. Confirmation of the formation of benzoquinone and dihydroxybenzene as the principal products comes from product separation and spectroscopic characterization, HPLC, and TLC. 4‐Chlorocatechol is also produced, while the main inorganic products are shown to be chloride and sulphate ions. Ru(bpy)2+3 is regenerated in the reaction scheme, making this an overall catalytic process. Prolonged irradiation leads to further degradation into CO2 and HCL. From the study of the kinetics of the reactions and considerations of literature data, a mechanistic scheme is presented.
I. Experimental Facts: Water‐Nonionic Surfactant Systems, and the Effect of Additives
Authors: Strey R.
Published: July 2012

In this introductory article we approach microemulsions from the binary water‐surfactant side. Model systems of the water ‐ nonionic surfactant (CiEj) type are examined. Many features of microemulsions are observable in these binary systems. As such we discuss the dependence of the cloud points on i and j, the temperature dependence of the viscosity within the micellar phase, and the formation of dilute bilayer phases. The effect of additives is examined, as it permits to gain insight into the structures and interactions. Towards the end of the paper the most important additive for microemulsion formation, the oil, is considered. A special feature of long‐chain surfactants is highlighted, namely, non‐monotonic critical lines leading to very peculiar two‐phase lobes as precursors to the formation of the three‐phase bodies.
Wetting, Unbinding, and Ultralow Tensions in Amphiphilic Systems
Authors: Schick M.
Published: July 2012

Wetting phenomena in ternary amphiphilic systems is reviewed with a particular emphasis on the effect of fluctuations on the location of the wetting transition, both in balanced and unbalanced systems. A rich prewetting behavior, yet to be observed, is also described. Unbinding transitions of lamellar phases in these systems are related to their wetting counterparts, and the possibility of observing a pre‐unbinding transition is discussed. It is shown that were a complete unbinding of a lamellar phase to occur, the interfacial tension between oil and water phases coexisting with it would be identically zero. It is argued that the origin of the ultralow interfacial tensions in strong amphiphilic systems is the proximity to such an unbinding transition, one which is prevented by van der Waals forces. A consequence of this assumption is that the interfacial tension between oil and water phases coexisting with a structured phase of given wavelength should vary as the inverse square of that wavelength, a result confirmed by experiments on microemulsions.
Theory of Vesicles and Droplet Type Microemulsions: Configurational Entropy, Size Distribution, and Measurable Properties
Authors: Kegel Willem K. , Reiss Howard
Published: July 2012

A model of vesicles and droplet type microemulsions is presented. It is shown that the size distribution of the droplets (either vesicles or microemulsions) coexisting with excess fluid is determined in general by only two terms: the free energy of the interface between the drops and the continuous phase, and a size dependent entropic factor commonly referred to as ‘the entropy of mixing’. The last mentioned term arises from translational configurations of the droplets. In this work we use an estimate of the translational contribution as derived in earlier work. A conjecture of the finite size effects coupled to the entropy of the interfacial layer is made based on experimental data.

We treat the summation over the size distribution as an ‘effective partition function’ from which all relevant measurable properties are calculated. The necessity of invoking a curvature dependence of the interfacial tension is proved. For vesicles, their average size is shown to scale as the volume fraction raised to a universal power, whereas their polydispersity is fully determined by a universal coefficient.

Because of the existence of a finite preferred curvature, no such universal behavior is found for microemulsions. Approximate analytical expressions for their size, interfacial tension of the planar oil‐water interface, and polydispersity are obtained. A limit (though not a physical one) is found at which universal behavior is recovered.

The model is compared to experimental data found in the literature. Quantitative comparison reveals full agreement at a consistency level. Good agreement is found even when using only a single free parameter in the theory.

However, this comparison points to an additional size independent term in the size distribution.
III. Experimental Techniques: Small Angle Scattering Applied to Microemulsions
Authors: Glatter O. , Strey R. , Schubert K.‐V. , Kaler E. W.
Published: July 2012

We present a procedure for the evaluation of small‐angle scattering data from microemulsions. A model independent picture of the structures in the various one‐phase samples emerges from the Indirect Fourier Transformation analysis of the measured small‐angle neutron scattering (SANS) spectra. The data analysis makes no a priori assumptions about the type of structure. Rather, the pair distance distribution functions are so unique that an unambiguous assignment of spherical, cylindrical or planar geometry is possible. In addition, the scattering length density profile normal to the interface is obtained by a deconvolution technique. We have investigated the microstructures in the binary system water (D2O)/pentaethylene glycol monoperdeutero‐n‐dodecyl ether (C12D25E5) and in the ternary system (D2O)/pentaethylene glycol mono‐n‐dodecyl ether (C12E5)/perdeuterated n‐octane (C8D18) by small‐angle neutron scattering. Spherical, cylindrical and planar morphologies were induced by changing the temperature of samples with fixed compositions. The same structural sequence exists in both the binary and the ternary mixtures. The spherical, cylindrical and planar structures are observed for water‐rich samples by increasing temperature. For oil‐rich samples the same structural sequence occurs as function of decreasing temperature. Both for water‐rich and oil‐rich samples, increasing the surfactant concentration at a constant ratio of surfactant to either oil or water, appropriately, causes the structures become more concentrated, but preserves the local structure and its dimensions.
Structure of Microemulsions Studied by NMR
Authors: Lindman Björn , Olsson Ulf
Published: July 2012

We discuss the application of NMR to investigate microemulsion structure. There are mainly two important NMR experiments; relaxation and self‐diffusion studies. Of these two, self‐diffusion studies have been found to be particularly informative in that it is the only technique which can demonstrate bicontinuity in equilibrium microemulsions. Self‐diffusion coefficients of water, oil and surfactant can be obtained in the same experiment. For droplet microemulsions, the self‐diffusion coefficients of the surfactant and enclosed solvent correspond to the droplet diffusion coefficient, which in turn depends on its hydrodynamic radius and on interactions. The self‐diffusion coefficient of the continuous solvent is slightly reduced due to obstruction effects, which depends on the droplet shape. For bicontinuous structures, the solvent diffusion on both sides of the surfactant film as well as the surfactant diffusion within the film is monitored. In particular the diffusion of the two solvents depends on how the surfactant film curves. NMR relaxation is found to be useful in the studies of droplet microemulsions. It is very sensitive to the droplet size while at the same time being insensitive to interactions. The latter allows for reliable size information even at higher droplet concentrations.
Vapor‐Liquid Equilibrium of the Methanol‐tert‐Butyl Methyl Ether (MTBE) System
Authors: Coto Baudilio , Wiesenberg Ralf , Pando Concepción , Rubio Ramón G. , Renuncio Juan A. R.
Published: July 2012

Vapor‐liquid equilibrium data for the methanol‐tert‐butyl methyl ether (MTBE) system have been measured covering the whole concentration range at six temperatures between 298.15 and 338.15 K. A Gibbs‐Van Ness type apparatus for total vapor‐pressure measurements of binary mixtures has been used. Data reduction has been carried out by means of a modified Barker's method using a Padé approximant to describe the excess Gibbs energy The methanol‐MTBE mixtures show positive deviations from ideality. The calculated values for the excess Gibbs energy are moderately positive and only slightly temperature dependent. Excess enthalpy values calculated from the temperature dependence of the excess Gibbs energy are in agreement with experimental data found in the literature. The experimental data are analyzed in terms of the UNIQUAC model, several versions of the UNIFAC model, the Lattice‐Fluid model and the Lattice‐Fluid Associated Solution Model.
Surface Conductivity Measurements on AgCl Single Crystals Using Microelectrodes
Authors: Fleig J. , Noll F. , Maier J.
Published: July 2012

A sensitive method to detect highly conducting surface layers on macroscopic solid electrolyte single crystals is described: Impedance measurements using circular microelectrodes of varying diameter (5–20 μm) permit a quantitative evaluation of the conductivity and the thickness of surface layers. Imprint geometry and surface topology are measured by atomic force microscopy (AFM). Additional temperature dependent measurements of the point contact resistance yield the activation energy of the relevant transport process. The applicability of the method is demonstrated at the example of a highly conducting surface layer on AgCl caused by mechanical treatment. The effect is discussed in terms of defects of different dimensionality and different kinetic barriers.
Binding Equilibria of Multiazo Dyes with Polymeric Dye Transfer Inhibitors
Authors: Runge Frank , Detering Jürgen , Zwissler Georg , Boeckh Dieter , Schade Christian
Published: July 2012

Dye binding equilibria have been investigated for several anionic multiazo dyes and the polar polymers poly(N‐vinylpyrrolidone), poly(N‐vinylpiperidone), poly(N‐vinylcaprolactam), poly(N‐vinylimidazole) and poly(N‐vinylpyrrolidone)‐co‐(N‐vinylimidazole) in water at 25°C. Spectrophotometric analyses revealed a disparate behavior of four different dyes in the presence of increasing amounts of polymers. Equilibrium constants Kp for the interaction of C.I. Direct Red 80 with the polymers were determined by sorption studies. With an increasing dye/polymer ratio, Kp increases by 1–2 orders of magnitude, attains a maximum value and declines subsequently. These observations are explained by the well known polyelectrolyte character of dye/polymer adducts. The enthalpy ΔrH of the dye/polymer association reaction was determined by microcalorimetric measurements for several polymers and dyes. Inhibition of dye transfer to cotton fabric by the polymers was investigated in a detergent slurry under washing conditions. Qualitatively, spectrophotometric, sorption and microcalorimetric studies agree with the result of the laundering experiments, suggesting that dye/polymer adduct formation operates as an underlying mechanism in modern “color”‐brand detergents.
Properties of regioselectively substituted anionic cellulose polyelectrolytes
Authors: Klemm Dieter , Heinze Thomas , Wagenknecht Wolfgang
Published: July 2012

In relation to recent results of regioselective reactions in cellulose chemistry, the synthesis and properties of important cellulose polyelectrolytes, namely of carboxymethyl cellulose and cellulose sulfate are described. Synthesis paths leading to such cellulose polyelectrolytes with an unusual pattern of the distribution of functional groups were developed using protecting group technique, activation effects, as well as phase separation phenomena. The regioselective distribution of functional groups within the anhydroglucose repeating unit at fixed degree of substitution and along the polymer chain is shown to be especially relevant, e.g., to solubility, salt tolerance, and interaction with human blood.
Further developments on polyelectrolyte coupled dynamics
Authors: Schmitz Kenneth S.
Published: July 2012

Generalized equations are presented for the interpretation of dynamic light scattering from multicomponent component systems, where the cumulant analysis and mutual diffusion approaches are distinguished. These equations are then applied to a “salt‐free” system, with specific emphasis on the dynamics of “ordered clusters” that have been observed for some highly charged systems. The short comings of the approximations employed as to the interpretation of real data are discussed in detail, and suggestions are made for future studies.
Kinetics of complexation of heavy metal ions with polyelectrolytes in aqueous solution
Authors: Hermeier Imke , Herzig Matthias , Knoche Wilhelm , Pohlmeier Andreas , Narres Hans‐Dieter
Published: July 2012

The kinetics of the binding of Ni2+ to polycarboxylate anions have been studied using pressure‐ and temperature‐jump relaxation techniques. The reaction proceeds via the two‐step Eigen mechanisms: free ions form the outer‐sphere and in the second step the inner‐sphere complex. The outer‐sphere complex is exceptionally stable due to the polyelectrolyte effect, and the electrical potential at the polyelectrolyte surface is estimated to be ψ ≈−86 mV. The rate constant for the formation of the inner‐sphere complex is in the same range as that obtained for Ni2+ complexes with small anions. The formation of bidentate complexes does not contribute significantly to the stability of the complexes. A parallel study of the reactions of Ni2+ with malonate and succinate has been performed.
The critical micelle concentration for the solution of polyelectrolyte/neutral block‐copolymers
Authors: Shusharina Nadezhda P. , Saphonov Maxim V. , Nyrkova Irina A. , Khalatur Pavel G. , Khokhlov Alexei R.
Published: July 2012

The problem of the micelle formation in the solution of diblock copolymers with one polyelectrolyte and one neutral block in selective solvent is considered. It is shown that the application of scaling arguments of Alexander‐de Gennes type to this problem leads to the “open association” picture of the micelle formation. The size distribution function for the micelles in the vicinity of critical micelle concentration (c.m.c.) is rather broad and does not have a pronounced bimodal character. The c.m.c. itself is manifested by the occurrence of the inflection point on the micelles size distribution function. These conclusions are supported by computer simulations. This picture is in contradiction with most of experimental observations which correspond to “closed association”. Therefore, more experimental and theoretical work is required to achieve an adequate understanding of the structure formation at c.m.c. for block‐copolymer solutions.
Polyelectrolyte brushes and polyelectrolyte adsorption layers
Authors: Fleer G. J.
Published: July 2012

The structure of brushes and adsorption layers of polyelectrolytes containing strong and weak groups is analysed, using both a numerical self‐consistent‐field (SCF) model and approximate analytical expressions. The latter are based upon a local electroneutrality approximation (brushes) or upon a mutual compensation of the adsorbed polymer charge and the diffuse double layer charge (adsorption layers); under most conditions excellent agreement with the SCF model is obtained.

Brushes with strong groups are relatively compact at high ionic strength and the brush thickness increases monotonously as the salt concentration is reduced. On the other hand, in “weak” brushes the root‐mean‐square thickness passes through a maximum as a function of the salt concentration, because the weak groups will discharge themselves at low ionic strength. Such a charge regulation is impossible for strong groups.

For adsorption layers, the adsorbed amount is high when the polymer is weakly charged and it decreases as the polymer charge is increased. This general trend is the same for strong and weak groups. However, weak groups can again adjust their charge. As a result, at intermediate charge densities their degree of dissociation is much lower than in the bulk solution; consequently the adsorbed amount is much higher than for strong groups.
Effects of surface topography, ph and salt on the adsorption of polydisperse polyethylenimine onto pulp fibers
Authors: Alince B. , Vanerek A. , van de Ven T. G. M.
Published: July 2012

The adsorption of polyelectrolytes on pulp fibers is complicated by the complex surface topography of the fibers, which are porous and fibrillated. The porosity and fibrillation determine to a large degree the internal and external surface area of the fibers accessible for polymer or polyelectrolyte adsorption. Other complications in practical applications are that the polyelectrolytes used are usually polydisperse and the ionic strength and pH are not always well controlled, all of which affect the adsorption.

From a comparison of the adsorption behavior of polydisperse polyethylenimine (PEI) onto smooth glass fibers with than on pulp fibers under well‐controlled conditions, a consistent model for PEI adsorption onto pulp fibers can be deduced. At low salt concentrations, PEI molecules are quasi‐irreversibly adsorbed. The high molecular weight fraction can be modeled as rigid spheres that deposit on the accessible surface, maintaining their shape. Low molecular weight fractions cover the spaces between the large molecules and also penetrate into the pores. The increase of PEI adsorption with pH is ascribed to a decrease in size of a PEI molecule with increasing pH. This results in a larger number of molecules that can be accommodated on the external surface and a larger fraction penetrating deeper into the porous structure as well. In the presence of salt (around 0.1 M), a dynamic equilibrium between adsorption and desorption is established.
The effect of cationic polyelectrolytes, containing terminal hydrophobic anchors, on the stability of vesicles of dioctadecyldimethylammonium chloride in calcium chloride solutions
Authors: Murphy Annette , Hill Alain , Vincent Brian
Published: July 2012

Dioctadecyldimethylammonium chloride (DODMAC) dispersions containing high concentrations of CaCl2 were stabilised using cationic polyelectrolytes with terminal hydrophobic anchors. The cationic polyelectrolytes were based on quarternised poly(vinyl‐2‐pyridine). The stability of the dispersions was dependent on the molecular weight of the polymer and the length of the hydrocarbon anchor. The amount of polyelectrolyte required to stabilise the dispersions was dependent on the type of polymer used and the concentration of salt in the dispersion. Some of the polymers were also capable of stabilising dispersions that were heated above the Lβ‐Lα phase transition temperature of the DODMAC vesicles. The polyelectrolytes that stabilised the dispersions most successfully in this study had molecular weights of about 10000‐20000 and hydrocarbon anchors containing 16 carbon atoms.
Transfer of cationic polyelectrolytes between cellulosic fibres and calcium carbonate particles
Authors: Lundqvist Åsa , Ödberg Lars , Glad‐Nordmark Gunborg
Published: July 2012

The transfer of a high molecular weight cationic polyacrylamide between cellulosic fibres and calcium carbonate particles has been studied in a stirred dispersion. It was found that there is a transfer also at very short times (5 s). The final distribution between fibres and fillers depend on the time the polymer has been adsorbed on the cellulosic fibres before the filler particles are added. If the polymer has been adsorbed a short time on the fibres, it does not have the opportunity to interact with the charges in the porcs of the fibres. The distribution will in this case be given by the outer surface areas of the fibres and fillers respectively since the particles have approximately the same z‐potential. If the polymer has been adsorbed a long time it can interact with more charges on the cellulosic fibre. The final distribution of the polymer between fibres and filler particles is for this case approximately determined by the charges available for interaction as given by the adsorption isotherms. The influence of addition level and stirring rate is in line with these arguments.

Hydrodynamic forces have a larger effect on larger particles which leads to faster transfer. A higher electrolyte concentration also seems to facilitate transfer. The reason is most likely that the polymers are less tightly bound to the fibres in this case. It has been shown, by adsorbing the polymer on the filler particles, that there is also a transfer of polymer from filler to fibre.
Polyelectrolytes interacting with interfaces: Surface forces and theoretical results
Authors: Dahlgren Mats A. G. , Hollenberg Heleen C. M.
Published: July 2012

The order in which salt and polyelectrolyte is added to a solution influences the structure of the adsorbed polyelectrolyte on surfaces in contact with the solution, and the interactions between surfaces across such solutions. These effects were investigated using the interferometric surface force technique. The results show that in low ionic strength (0. 1 mM KBr), there is a strong attraction between two mica surfaces covered with oppositely charged Polyelectrolytes. When the ionic strength is increased (up to 100 mM KBr), a long‐ranged repulsion is developing. This repulsion is more long ranged and larger in magnitude when the salt is added before the polyelectrolyte than when salt is added to a system which already contains polyelectrolyte. This indicates a more extended adsorbed layer when the adsorption is carried out directly from the higher ionic strength solution. This more extended adsorbed layer is irreversibly compressed upon the first approach of the surfaces. Mean field calculations (Scheutjens‐Fleer model) were used to rationalize experimental findings. The results from these calculations show that the adsorbed layer is much more extended in high ionic strength solutions, which is in good agreement with the experimental results.
Polyelectrolyte‐surfactant association at solid surfaces
Authors: Claesson Per M. , Dedinaite Andra , Blomberg Eva , Sergeyev Vladimir G.
Published: July 2012

The interferometric surface force technique has been utilized for studying the interaction between negatively charged surfaces coated with a cationic polyelectrolyte across solutions of anionic surfactant, sodium dodecyl sulphate (SDS). The polyelectrolyte used was poly ([2‐(propionyloxy)ethyl]trimethylammonium chloride), PCMA, which has one positive charge per segment. At low ionic strength the polyelectrolyte adsorbs in a flat conformation and neutralizes the negative mica surface charge. The interaction forces between the polyelectrolyte‐coated surfaces are dominated by a strongly attractive force at distances shorter than about 150 Å.

Addition of SDS into the measuring chamber to a concentration of about 0. 1 cmc changes the interaction forces dramatically. The long‐range forces are now repulsive due to a recharging of the surfaces. The polyelectrolyte layer also swells considerably and, more surprisingly, the force versus distance profile displays clear oscillations. We interpret these oscillations as being caused by the spatial arrangement of SDS micelles stabilized by the polyelectrolyte. The oscillations in the force curve remain as the SDS concentration is increased to cmc. The interaction forces and the layer structure for the PCMA/SDS system are very different compared to those observed for weakly charged polyelectrolyte/SDS and lysozyme/SDS systems. The differences can be rationalized by considering that low charge density polyelectrolytes and lysozyme, a compact cationic globular protein, cannot equally efficiently stabilize SDS micelles as a flexible high charge density cationic polyelectrolyte such as PCMA.
Chemical imaging of single polyethylenimine polymers by chemical force microscopy
Authors: Akari S. , Schrepp W. , Horn D.
Published: July 2012

Polymer adsorption effects are of prime importance in technical applications ix. for flocculation in paper making or the cleaning of waste water. In this paper we report on the direct imaging of single polyethylenimine polymers adsorbed on negatively charged latex spheres. Chemical imaging was achieved by a proper chemical modification of the tip of a conventional scanning force microscope. The imaging was performed by operating the microscope in the friction mode thus giving information about the adhesion properties of the polymers under investigation. Imaging is even possible in an aqueous environment. The results are in good agreement with quasi elastic light scattering measurements and former models of the mechanism of action of polyethylenimine in flocculation processes.
Polyelectrolyte complexes at interfaces
Authors: Laschewsky André , Mayer Bernd , Wischerhoff Erik , Arys Xavier , Jonas Alain
Published: July 2012

Multilayers were built up by polyelectrolyte complexation at interfaces, using a number of new charged species, some of them with rather unusual features. Coloured species such as azo dyes were incorporated into the polycations, facilitating the analysis and serving as a probe of the local electronic environment. Copper/polyethylene‐imine complexes were used as polycations, the charges being provided by the complexed inorganic ions. Also, polymers carrying simultaneously positive and negative charges were employed as polycations for the multilayer assembly. Further, a low molar mass azo dye bearing four negative charges was used instead of the polyanion poly(vinylsulfate). The resulting multilayers were studied by optical methods, UV/VIS‐spectrometry and X‐ray reflectometry. The deposition process is reproducible and provides uniform coatings. The thicknesses of the internal layers and their evolutions with distance from the substrate are strongly dependent on the details of the adsorption process and on the chemical structure of the polyions. The results demonstrate the tolerance of this method of multilayer build‐up to a variety of strongly different molecular structures.
Dielectric relaxation spectroscopy of electrolyte solutions: ZnCl2 in N‐methyl‐2‐pyrrolidone, tetramethylurea and ethylacetate
Authors: Brockmann U. , Stockhausen M.
Published: July 2012

The dielectric spectra of the title systems (with moderate to high salt concentrations) have been measured between MHz frequencies and 72 GHz at 20, 40 and 60 °C (EtAc only 20 °C). Apart from the conductivity contribution, there are two evidently discernible relaxation contributions. These are ascribed to unaffected solvent (at higher frequencies) and, on the other hand, to affected solvent and to ionic species (at lower frequencies). The nature of the latter and their relaxation mechanism are discussed by comparing the respective relaxation parameters with those of other liquid systems.
33S nuclear quadrupole coupling in the microwave spectrum of methylthiocyanate
Authors: Hansen N. , Hartwig H. , Kretschmer U. , Mäder H.
Published: July 2012

The rotational spectrum of 33S‐methylthiocyanate in the vibrational ground state was observed in natural abundance by molecular beam Fourier transform microwave (MB‐FTMW) spectroscopy. We were able to determine the rotational and centrifugal distortion constants, the methyl internal rotation parameters, and the 14N and 33S quadrupole coupling constants. The rotational constants were found to be A = 15598.104(83) MHz, B = 4144.5631 (3) MHz and C = 3338.1246(2) MHz. For the torsional ground state (A‐species) the 33S nuclear quadrupole coupling constants were obtained as χaa = −40.513 (4) MHz, χbb = −7.166 (6) MHz and χcc = 47.679(7) MHz. The corresponding constants for the E‐species lines agree with these values within the given error limits. Additionally the rotational and centrifugal distortion constants, the methyl internal rotation, and the 14N quadrupole coupling constants for the 32S‐ and 34S‐isotopomer could be improved.
Spectroelectrochemical investigations of polyxylidines
Authors: Probst Matthias , Holze Rudolf
Published: July 2012

Aniline derivatives carrying two methyl substituents in different ring positions (2,3‐, 2,5‐ and 2,6‐xylidine) were polymerised electrochemically. The obtained polymers were characterised by cyclic voltammetry, in situ UV‐vis spectroscopy and in situ Resonance Raman spectroscopy. With poly(2,5‐xylidine) in situ conductivity measurements were performed. The polymers show various degrees of electrochromism. Vibrational spectra of poly(2,3‐xylidine) and poly(2,5‐xylidine) show a reversible change of the ring from a benzoid into a quinoid state depending upon the degree of oxidation. A structure analogous to the one proposed for polyaniline is suggested.
Networks of hydrogen bonds between pyridones ‐ structure breaking effects by organic solvents and sensor applications
Authors: Dickert F. L. , Keppler M. , Zwissler G. K. , Obermeier E.
Published: July 2012

Pyridone shows self‐assembling properties via hydrogen bonds as can be shown by IR‐spectroscopy. In this way networks are formed by intermolecular interaction of tris‐(2‐pyridone‐5‐carbonacid)‐glycerol ester, each molecule containing three units of pyridone. The structure breaking effect of organic solvents leads to a reduced ordering of this material and can be observed directly by hyperchromic changes of the UV‐absorbance. This process is traced by capacity measurements as the unpaired structures of pyridone possess a strong dipole moment. For this purpose the permittivity of an interdigital capacitor (IDC) coated with a thin solid film of the network‐forming material is measured in an atmosphere of organic solvent vapours.