bluuebunny/crossref_metadata_2025_split huggingface dataset:
Particularities in static and dynamic light scattering from branched polyelectrolytes in comparison to their linear analogues
Authors: Burchard Walther , Frank Markus , Michel Eduard 
Published: July 2012

AbstractThe expansion behaviour of branched strong polyelectrolytes when lowering the ionic strength was compared with the corresponding linear chains. Two pairs of polymers were chosen (a) linear poly(allylamine hydrochloride) with the corresponding intramolecularly crosslinked microgel and (b) cationic amylose derivatives with the corresponding derivative of potato starch that consists mainly of the branched amylopectin. The cationic group in the polysaccharides was a quaternized amine. As expected the expansion behaviour of the branched materials is considerably less than of the linear chains. Surprisingly the ratio of the radius of gyration to the hydrodynamic radius ρ=Rg/Rh showed opposite behaviour and increased for the linear chains (rod like behaviour) but decreased for the branched materials to sphere like behaviour when the ionic strength was lowered.A more detailed analysis of the structure was possible with the polysaccharides. Because of their large dimensions the angular dependence of the scattered light could be measured. The data were analysed from Kratky plots. The branched amylopectin showed no change in the self‐similarity when the ionic strength was lowered and could be described by a fractal dimension of about df = 2.2. Very different behaviour was found with the amylose derivative. A rod‐like structure was obtained at high ionic strength that underwent a transition to a disordered conformation that however, is not that of a random coil. Various model calculation were made which give evidence for a folded double helix with loops in between. At low ionic strength the two double‐helix section unfold and the loop strongly expands.
Scattering properties of weakly charged polyelectrolytes
Authors: Borsali Redouane 
Published: July 2012

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

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

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

AbstractThe counter ion condensation to the polyelectrolytes polyacrylate (PAA) and poly(maleate/acrylate)copolymer (MAC) was measured for Na+−, K+−, Ca2+−, Cd2+, and Cu2+−ions in aqueous solutions by means of ion‐selective electrodes. The competition between monovalent and divalent ions was investigated. From the studies an order of counter ion effectiveness was obtained: Na+ binds stronger than K+ and Cu2+ stronger than Cd2+ and these two much stronger than Ca2+.The pressure dependence of Cd2+ condensation in competition to the large TRIS+ ions was determined in the pressure range from 0.1 to 500 MPa. The results indicate a volume increase of about 14ml/mol when Cd2+ is bound to the polyelectrolytes PAA or MAC. This leads to the conclusion that cadmium ions become dehydrated during the condensation process.
Marked discreteness on the coil‐globule transition of single duplex DNA
Authors: Yoshikawa K. , Kidoaki S. , Takahashi M. , Vasilevskaya V. V. , Khokhlov A. R. 
Published: July 2012

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

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

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

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

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

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

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

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

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

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

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

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

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

AbstractVibrational relaxation of highly excited ground state 1,3,5‐Cycloheptatriene (CHT) has been investigated by picosecond transient absorption spectroscopy in gases (nitrogen and ethane) at pressures up to 200 bar and in the liquid solvents ethane, heptane, C2Cl3F3 and methanol. The results show that in the gas phase, the relaxation rates are proportional to the bath gas density within the studied pressure range. In contrast, the relaxation in liquids is significantly slower than predicted by common models for the collision frequency at high densities.