bluuebunny/crossref_metadata_2025_split huggingface dataset:
III. Experimental Techniques: Small Angle Scattering Applied to Microemulsions
Authors: Glatter O. , Strey R. , Schubert K.‐V. , Kaler E. W. 
Published: July 2012

AbstractWe 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

AbstractWe 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

AbstractVapor‐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

AbstractA 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

AbstractDye 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

AbstractIn 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

AbstractGeneralized 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractDioctadecyldimethylammonium 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractPolymer 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

AbstractMultilayers 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

AbstractThe 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

AbstractThe 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.