bluuebunny/crossref_metadata_2025_split huggingface dataset:
Time Resolved Studies of Intermediate Products in the Oxidation of HCFC 141b (CFCl2CH3) and HCFC 142 b (CF2ClCH3)
Authors: Mörs V. , Hoffmann A. , Malms W. , Zellner R. 
Published: July 2012

AbstractThe oxidative degradation of HCFC 141 b (CFCl2CH3) and HCFC 142 b (CF2ClCH3) in the presence of NO at T = 293 K and p = 50 mbar has been studied using laser pulse initiation combined with cw laser long path absorption/LiF for the detection of OH and NO2. The absolute yield and temporal behaviour of these products have been found to be sensitive indicators for the reaction behaviour of the alkoxy radicals CFCl2CH2O and CF2ClCH2O, respectively. The rate coefficients for the reactions of the alkoxy radicals with O2 were determined to be k(CFCl2CH2O+O2→CFCl2CHO+HO2) = (2.0±1.0)×10−15 cm3/s and k(CF2ClCH2O+O2→CF2ClCHO+HO2) = (2.5±1.5)×10−15 cm3/s. Upper limits for the rate coefficients for unimolecular decomposition of the alkoxy radicals by C‐C‐bond fission of k(CFCl2CH2O+M→CFCl2+CH2O+M)×1.0±103 s−1 and k(CF2ClCH2O+M→CF2Cl+CH2O+M)≤1.5 T≤ 103 s−1 were derived. We conclude from these data that CFCl2CHO and CF2ClCHO will be formed as the dominant primary carbonyl products in the oxidation of HCFC 141 b and 142 b throughout the troposphere. Moreover, the rate coefficients for the reactions of the HCFCs with OH radicals at T = 293 K have been measured. The values k(CFCl2CH3+OH→CFCl2CH2+H2O) = (4.6±0.8)×10−15 cm3/s and k(CF2ClCH3+OH→CF2ClCH2+H2O) = (2.6±0.4)×10−15 cm3/s were obtained.
Determination of the Pressure‐Dependent Rate Constant CFO+O2 in a F/F2/CHFO/O2 Gas Mixture at 298 K
Authors: Behr Peter , Heydtmann Horst 
Published: July 2012

AbstractHomogeneous gas phase reactions in F/F2/CHFO mixtures with helium as a bath gas were studied pure and with addition of oxygen at ambient temperature. A computer‐controlled discharge flow system with mass spectrometric detection was used. The accessible pressure range was 1.6–3.5 mbar. A more precise value for the reaction CFO+CFO→CF2O+CO was determined: k(2a)=(1.7+0.4−0.3)·10−11 cm3 molecules−1 s−1. No discernible pressure dependence was found for CFO+F→CF2O: k(3a) = (5.0+3.3−1.4)·10−12 cm3 molecules−1 s−1. Fluoroformyl peroxy radicals were formed by CFO+O2+M→CF(O)O2+M. The pressure dependence of this reaction could be described by k0(4) = (4.5+2.2−1.1)·10−31 cm−6 molecules−2 s−1 and k·(4) = (1.7±0.3)×10−12 cm3 molecules−1 s−1. A small bath gas dependence of k(4) was noted.
Growth of Nanocrystalline Platinum in a Zeolite Host ‐ An in Situ X‐Ray Powder Diffraction Study
Authors: Schnell Ralf , Fuess Hartmut 
Published: July 2012

AbstractThe growth of nanocrystalline platinum particles in zeolite [Pt(NH3)4]NAX was investigated by in situ X‐ray diffraction in combination with Rietveld refinement atT= 509, 519, 530 and 562 K. The reaction was directly followed by the gradual decrease of the Pt2+‐occupation and the simultaneous increase of the metallic platinum particles, which grow up to an average size of 4 nm. An increase of the zeolite lattice constant and a gradual decomposition of the framework up to 20% were simultaneously observed.The process of crystal growth can be influenced by the preparation conditions of the zeolite. After dehydration up to 383 K at 10−7bar more than 90% of the platinum cations are located near the centre of the 12‐ring‐window. Dehydration in the temperature range from 403 to 443 K under vacuo results in a partial shift of the platinum cations to a second position and to an increase of the reactivity.
Copolymers of acrylamide and quaternary ammonium cationic monomers: Characterization by HPLC and copolymer composition control
Authors: Hernández‐Barajas Jose , Hunkeler David 
Published: July 2012

AbstractCopolymers of acrylamide with quaternary ammonium cationic monomers (dimethylaminoethylacrylate‐methyl chloride, DMAEA and dimethylaminoethylmethacrylate‐methyl chloride, DMAEM) have been synthesized by inverse‐emulsion copolymerization using both sorbitan monoleate (SMO) and a block copolymeric surfactant (HB246) whose hydrophilic moiety is polyethylene oxide and whose hydrophobic moiety is poly‐12 hydroxy stearic acid. Residual monomer concentrations were determined by means of an optimized HPLC method using a CN coated column. The optimized conditions consist of an acetonitrile‐water mobile phase with a ratio of 50:50 vol% with dibutylamine used as an additive to reduce the adsorption of the cationic monomer at a concentration of 0.01 M and phosphoric acid to adjust the pH. The results indicate that the choice of surfactant influences strongly the quality of the copolymers produced. For example, more uniform copolymers of acrylamide and DMAEA can be synthesized using the block copolymeric surfactant (HB246) at faster production rates in comparison with sorbitan monoleate (SMO). However, a composition drift is observed in the inverse‐emulsion copolymerization of acrylamide and DMAEM using HB246. It is shown that uniform water soluble copolymers of acrylamide and DMAEM can be produced by implementing semi‐batch policies with non time‐varying feed‐rates.
Charge transport in polyelectrolyte solutions
Authors: Turq P. , Bernard O. , Simonin J. P. , Durand‐Vidal S. , Barthel J. , Blum L. 
Published: July 2012

AbstractThe concept of apparent charge is a convenient tool for the description of electrical effects on polyelectrolytes in solution. The apparent charge can be significantly lower than the structural charge. The difference between these two parameters provides information on the interactions between the particle and the surrounding medium. Assessment of the physical contribution to the apparent charge can be made with the use of modern electrolyte theories; chemical speciation processes can be described by suitable chemical models.
Polyelectrolyte simulation
Authors: Seidel Christian 
Published: July 2012

AbstractWe present results of a Monte Carlo simulation of weakly charged chains at infinite dilution but with added salt. The charges on the chain interact with a screened Coulomb potential of the Debye‐Hückel type. Trial chain configurations are generated by means of the Pivot algorithm which is shown to exhibit short relaxation times also with Coulomb interaction. The extension of the coils as well as their shape is discussed for varying solution conditions characterized by the screening parameter ζ = 2λD/b where λD is the Debye length and b is the contour distance between neighbouring charged segments. There is an evident influence of the flexibility of the underlying neutral chain on properties of the charged chain. The resulting behaviour of the electrostatic persistence length is compared with predictions recently made by Barrat and Joanny.
Ising models and acid‐base properties of weak polyelectrolytes
Authors: Borkovec Michal , Koper Ger J. M. 
Published: July 2012

AbstractIonization equilibria of weak polyelectrolytes and their oligomeric analogs are discussed in terms of the Ising model. Within the Ising model one treats the thermal statistics of a collection of interacting sites, which can be either protonated or deprotonated. The basic parameters of the model are microscopic pK values of individual groups and various interaction parameters between pairs and possibly triplets of sites. By performing the appropriate thermal average, one can obtain the titration curve of the system considered. For systems with finite number of ionizable sites, we recover the classical description in terms of successive protonation equilibria. Thereby one can express the ionization constants in terms of the interaction parameters. For system with infinite number of sites, such as linear polyelectrolytes, the titration curves can be also calculated explicitly. We discuss three illustrative examples in more detail: (i) a simple model for linear, weak polyelectrolytes; (ii) a refined model for same type of system which describes poly(ethylene imine) and its oligomeric analogs quantitatively; (iii) simple mean‐filed model for polymeric interfaces, such as the surface carboxylated latex particles.
Polarized and depolarized dynamic light scattering of a rodlike polyelectrolyte in a strong acid
Authors: Sohn D. , Russo P. S. , Roitman D. B. 
Published: July 2012

AbstractUnusual dynamic light scattering behavior of poly(benzoxazole), a stiff backbone rodlike polymer, has been found in methane sulfonic acid/methane sulfonic acid anhydride. A very rapid, angle‐independent decay mode characterized the short‐time autocorrelation functions at various levels of added salt, sodium methane sulfonate, in both polarized and depolarized dynamic light scattering experiments. In some ways, the behavior qualitatively resembles the long‐predicted “plasmon” mode, which has never been seen in more conventional polyelectrolyte systems. However, calculations based on a point charge model are inconsistent with the plasmon mode, even allowing for the high viscosity of the methane sulfonic acid solvent. The absence of angle dependence means that the rapid decay mode cannot be explained by the diffusion of oligomers. The meaning of the rapid, angle‐independent decay mode remains unclear.
Structure and dynamics of polyelectrolyte solutions with multivalent salts
Authors: Drifford Maurice , Dalbiez Jean‐Pierre , Delsanti Michel , Belloni Luc 
Published: July 2012

AbstractAqueous solutions of highly charged polyelectrolyte solutions phase separate in the presence of multivalent salts. Phase diagrams of sodium polystyrene sulfonate (Na+PSS−) with LaCl3, Th(NO3)4 were studied over a wide range of polyelectrolyte and salt concentrations. The concentration of salt at the transition C was found to be proportional to the monomer concentration Cm and nearly molecular weight independent: C/Cm≅0.23 for La3+ and C/Cm≅0.12 for Th4+. With further addition of salt a new transition from a two phase system back to a single phase was observed at constant salt concentration independent of NaPSS concentration but sensitive to molecular weight. A theoretical model which explains this behavior in termes of electrostatic attractive interaction between monomers due to the high valency of condensated counterions has been developped recently. The form of the phase diagram results from a competition between the classical long range Coulombic interaction, the short range bridging attraction via the condensed counterion and the electrostatic screening.Dynamic light scattering measurements were performed in the lower monophase solution as a function of NaPSS concentration and over a wide LaCl3 concentration range. Two relaxation times were observed at very low salt concentration.The dynamic studies reveal some interesting behaviours of apparent diffusion coefficient as a function of polyelectrolyte and salt concentrations (Cm, Cs): i) a q2 dependence of the fast mode and a q3 dependence of the slow mode; ii) the power law Dfast varies approximately as C1/2m at constant low salt concentration. This mode can be explained assuming cooperative diffusion in a transient polyelectrolyte network.The slow mode of the bimodal decay disappears increasing the added salt (LaCl3) concentration at constant Cm. It is concluded that the slow mode is related to labile clusters or temporal domains of polyelectrolyte chains which are formed in solutions at low concentration of added salt. Both the disappearance of the slow mode on a very long time scale and the non reappearance of this mode when cycling at constant Cs/Cm between high and low salt concentration indicate that low salt or salt free polyelectrolyte solutions tend very slowly to thermodynamic equilibrium.
Ion‐ion correlations and effective charges in electrolyte and macroion systems
Authors: Kjellander Roland 
Published: July 2012

AbstractVarious ion‐ion correlation mechanisms that affect double layer interactions between charged macroparticles in electrolyte solutions are reviewed and discussed. Such effects give rise to quantitative and sometimes qualitative deviation from the prediction of the Poisson‐Boltzmann theory. Special attention is given to the attractive double layer interactions that can appear between equally charged surfaces at short surface separations for aqueous systems with divalent counterions. The long‐range behaviour of the double layer interaction is also treated. It is efficiently described in terms of effective surface charge densities, which summarizes how the inner parts of the diffuse double layer affects the distant parts. The magnitude as well as the sign of the effective charge depends on the state of the system. Charge reversal can occur for aqueous systems with divalent counterions. A major objective of the paper is to describe and illustrate the mechanisms in a simple and graphical manner.
Attraction of pure electrostatic origin between small colloids
Authors: Belloni Luc , Spalla Olivier 
Published: July 2012

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

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

AbstractThe adsorption of polyelectrolyte, sodiumcarboxymethyl‐cellulose (Na‐CMC) on Aerosil (SiO2) particles is studied by means of electric light scattering and electrophoresis. The electro‐optical effect α increases with the rise of polyelectrolyte concentration. Simultaneously the increase of particles' electrophoretic mobility reveals the adsorption of polyion on identically charged particles. The similarity of the frequency dependence of the electrooptic effect at different polyelectrolyte concentrations is an indication that the particles' induced dipole moment is mainly determined by polyelectrolyte' counterions behaviour.Two relaxations of the electro‐optical effect are observed at frequencies ranging from 500 Hz to 100 kHz the first relaxation is about 1 kHz, the second one ‐ in the 10 kHz region. The increase of charge density parameter ζ doesn't influence the first relaxation, but the second one becomes wider and more noticeable. According to Manning predictions the rising of ζ(ζ>1) results in the increase of the fraction of diffuse counterions. So their contribution to the induced dipole moment is more clearly demonstrated in the frequency dependence. Most probably the first relaxation of α is connected with the “bound” counterions whereas the second is due to the diffuse counterions. In the case of polyelectrolyte adsorption on the particles of the same charge sign an analogy with Manning consideration for free polyelectrolytes in solution could be drawn.
Stoichiometry and structure of polyelectrolyte complex particles in diluted solutions
Authors: Dautzenberg Herbert , Hartmann Jürgen , Grunewald Steffi , Brand Fabien 
Published: July 2012

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

AbstractCo‐operative interaction between water‐soluble polymers has been a topic of investigation world‐wide because of their importance from both scientific and practical viewpoint.Our work is focused on the investigation of complex formation between oppositely charged polyelectrolytes and the interaction with inorganic fine particles for example negatively charged quartz powder and silicic acid. The cationic polyelectrolytes tested were poly(diallyldimethylammoniumchloride) (PDADMAC) and polyallylamine (PAA), differing in the molar mass, the molecular geometry and charge density. The anionic polyelectrolytes used were copolymers of maleic acid with propylene (MS‐P), styrene (MS‐Sty) and methylstyrene (MS‐α‐MeSty).Two different principles of surface modification with polyelectrolyte complexes were tested. On the first hand previous prepared non‐stoichiometric complex dispersions carrying cationic excess charges were contacted to the substrate and on the other hand the polycation was preadsorbed on the oppositely charged surface before an equimolar amount of polyanion was added. Both methods show different results in the reachable surface charge. It is important to note that a synergistic effect with respect to the cationic surface charge was found in dependence on the surface charge density of the substrate, the chosen polyelectrolyte combinations and the used modification procedure. From the results it is concluded that steric factors of the polyelectrolytes are responsible for conformation and stoichiometry of the formed polyelectrolyte complexes and thus the effectiveness of charge modification with polyelectrolyte complex is also determined by the characteristics of the used polyions.
Immobilisation of biological matter by polyelectrolyte complex formation
Authors: Dautzenberg H. , Lukanoff B. , Eckert U. , Tiersch B. , Schuldt U. 
Published: July 2012

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

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

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