bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calcium induced volume transition in polyelectrolyte gels
Authors: Horkay Ferenc , Basser Peter J. , Hecht Anne‐Marie , Geissler Erik 
Published: October 2003

AbstractThe osmotic properties and the small angle neutron scattering (SANS) behaviour of fully neutralized sodium polyacrylate gels are investigated in the presence of calcium ions. Analysis of the SANS response displays three characteristic length scales, two of which are of thermodynamic origin, while the third, associated with the frozen‐in structural inhomogeneities, is static. The SANS results are consistent with direct osmotic observations which indicate that the thermodynamic properties cannot be adequately described by a single correlation length. The concentration dependence of the osmotic pressure displays a power law behaviour with an exponent that decreases with increasing calcium concentration.
Hyperelasticity and stress softening of filler reinforced polymer networks
Authors: Klüppel Manfred 
Published: October 2003

AbstractStarting from an analysis of filler networking in bulk polymers, a constitutive micro‐mechanical model of stress softening and hysteresis of filler reinforced polymer networks is developed. It refers to a non‐affine tube model of rubber elasticity, including hydrodynamic amplification of the rubber matrix by a fraction of hard, rigid filler clusters with filler‐filler bonds in the unbroken, virgin state. The filler‐induced hysteresis is described by an anisotropic free energy density, considering the cyclic breakdown and re‐aggregation of the residual fraction of soft filler clusters with already broken, damaged filler‐filler bonds. Experimental investigations of the quasi‐static stress‐strain behaviour of silica and carbon black filled rubbers up to large strain agree well with adaptations found by the developed model. The microscopic material parameters obtained appear reasonable, providing information on the mean size and distribution width of filler clusters, the tensile strength of filler‐filler bonds and the polymer network chain density.
Reinforced superabsorbent polyacrylamide hydrogels
Authors: Philippova Olga E. , Zaroslov Yuri D. , Khokhlov Alexei R. , Wegner Gerhard 
Published: October 2003

AbstractThe ability of linear stiff‐chain poly(sodium p‐phenylenesulfonate) to self‐assemble in aqueous media with the formation of rodlike aggregates was used to immobilize it in a polyacrylamide network without covalent bonding. It was shown that polyelectrolyte rods impart simultaneously two useful properties to the gel: higher ability to absorb water and higher mechanical strength. The counterions of charged rods ensure the enhancement of the absorption capacity of the gel, while stiff elements strengthen the gel. This makes such systems potentially promising as superabsorbent materials.
Outstanding covalent conjugated gels: electrically conducting rubbers
Authors: Pépin‐Donat Brigitte , Viallat Annie 
Published: October 2003

AbstractFour series of fully conjugated poly(octylthiophene) gels were prepared by oxidative copolymerization of octylthiophene with four different cross‐links (trithienylbenzenes) of functionalities f=3 or 6 and by varying the cross‐link ratio R. The gels exhibit rubber elasticity and swell in apolar solvents. The gel fraction, the swelling ratio Q, the elastic modulus, and a NMR structural parameter display master curves of variations versus the variable fR, which characterises the statistical structure of the gels. This result shows that the linear chain segments comprised between adjacent cross‐links govern the deformation properties of the networks. Transport properties were explored. The gels are photoluminescent. When doped (oxidation by iodine), they are electronically conducting both in dry and swollen states. At large Q intra‐chain hopping mechanisms govern the conductivity while at small Q, intermolecular hopping processes are predominant. Cross‐links are not a limitation to conductivity.
Polymer gels and brushes at surfaces
Authors: Vilgis T.A. , Joanny J.F. , Johner A. 
Published: October 2003

AbstractWe discuss the adsorption of polymer gels on flat surfaces. Even in cases of complete wetting, where the spreading power S is positive and where an equivalent liquid would spread, the elastic stresses due to the gel deformation upon adsorption oppose spreading. The competition between elasticity characterized by the bulk shear modulus G and capillarity, characterized by the spreading power S, defines a typical length scale 1 = S/G for the deformation in the gel. Macroscopic gels larger than 1 deform only at their edges over a region of size 1. Microscopic gels show a finite deformation despite the elastic stresses. These results can be compared to confined polymer brushes.
Thermal and photo‐actuation in nematic elastomers
Authors: Warner Mark , Terentjev Eugene 
Published: October 2003

AbstractMono domain nematic elastomers change shape by as much as 400% on being heated from the nematic to isotropic state. The reason is that nematic order, Q, elongates the distribution of chains and thus the network that they form. Experimental evidence for this, and simple theory is presented. A novel method to change Q, and hence obtain an analogous elastic strain, is to bend the nematic's rods by photoisomerization. On absorbing a photon, photochromes such as azo rods leave the (straight) trans state and adopt the cis (bent) form. We show data and give simple theory to explain this remarkable, reversible elastic phenomenon.
Modelling auto‐acceleration in DGEBA/diamine systems
Authors: González M. , Kindelán M. , Cabanelas J.C. , Baselga J. 
Published: October 2003

AbstractCuring of epoxy resins with aliphatic diamines at low temperatures deviates from the 4EQ mechanism (catalytic and non‐catalytic dual path) at relatively low conversions, far from vitrification. Although the Horie mechanism relies on a third order reaction it is possible a more realistic approach to epoxy curing kinetics if a detailed analysis of auto‐acceleration is made. A single parameter dependent only on the nature of the amine is proposed.
Microscopic deformation of filler particles in rubber under uniaxial deformation
Authors: Belina Gábor , Urban Volker , Straube Ekkehard , Pyckhout‐Hintzen Wim , Klüppel Manfred , Heinrich Gert 
Published: October 2003

AbstractStructural studies of filled polymer networks under periodic deformation are of great importance to the industries concerned with rubber. The degree of reinforcement provided by the filler depends on a number of variables: the size of the polymer‐filler interface, the size of primary particles, the size and shape of filler clusters. In the tyre industry it is necessary to optimize mechanical properties such as low rolling resistance, good wet grip and long lifetime. There have been studies of unfilled polymer networks and filler model‐systems (block copolymers),[1,2] but because their complexity, industrial rubber samples have escaped investigations. We performed SAXS, USAXS and SANS measurements on carbon black filled natural rubber (poly‐isoprene) under uniaxial deformation at ESRF ID‐02 and Forschungszentrum Jülich KWS‐2. The scattering patterns of the studied filler particles show power‐law decay over many decades in scattering vector q. At the scale of primary particles we detected surface fractal behavior and for the characteristic size of the primary particles we calculated lengths of the order of 10 nm. X‐ray scattering was used for time resolved experiments (about 10 frames per second) and neutron scattering was used to distinguish between scattering from the studied fillers and the additives (especially zinc oxide) used in industrial materials.
Arabinoxylan networks as affected by ovalbumin content
Authors: Carvajal‐Millan Elizabeth , Surget Anne , Rouau Xavier , Guilbert Stéphane , Micard Valérie 
Published: October 2003

AbstractSolutions (1% w/v) of water‐extractable arabinoxylans (WEAX) from wheat were mixed with ovalbumin solutions at different concentrations in order to obtain different protein/polysaccharide ratios (0, 0.6, 2.5, 5.0, 7.5 and 10.0). These mixtures were oxidized by a laccase (Pycnoporus cinnabarinus). The kinetics of gelation was monitored by rheological measurements of the storage modulus (G′) and loss modulus (G″) at 25°C during 2 h. In the different ovalbumin/WEAX mixtures, WEAX cross‐linking occurred as shown by an increase in G′. However, final G′ decreased as a function of protein concentration from 17.2 Pa (WEAX) to 7.1 Pa (ovalbumin/WEAX=10), following a sigmoidal relationship. Ovalbumin is probably entrapped in a WEAX covalent network, which explains the changes in rheological properties, but it does not participate in the network formation. Ferulic acid oxidation and diferulic acid formation was delayed at ovalbumin/WEAX=5.0 until 40 min but not at the end of gelation. In the same mixture SH groups from ovalbumin oxidized more rapidly than the protein alone. Ovalbumin via SH groups are probably responsible for the FA oxidation delay and the weaker WEAX gel formed by blocking the enzymatically formed free radicals.
Rheological investigation of swollen gluten polymer networks: effects of process parameters on cross‐link density
Authors: Domenek Sandra , Morel Marie‐Hélène , Redl Andreas , Guilbert Steéphane 
Published: October 2003

AbstractWheat gluten samples were subjected to different thermo‐mechanical treatments. Kinetics of protein aggregation and changes in network structure were investigated through biochemical and rheological measurements. Temperature induced protein aggregation through disulphide cross‐links. Shear treatment alters the aggregation mechanism since a lower energy of activation was observed. Accumulation of aggregated protein enhances the elastic behaviour of the material. The strong correlation found between the extent of protein aggregation and the molecular weight between cross‐links reveals the important role of covalent bonds in the network connectivity.
Filler networks in elastomers
Authors: Ehrburger‐Dolle Françoise , Bley Françoise , Geissler Erik , Livet Frédéric , Morfin Isabelle , Rochas Cyrille 
Published: October 2003

AbstractElastomers are soft materials that can be reinforced by dispersing into them nanosized solid particles. Common examples of the latter are silica or carbon black aggregates. However, the mechanism of reinforcement is still not yet fully understood. Our work consists in investigating by small‐angle X‐ray scattering (SAXS) the structure of the aggregate network spreading throughout the matrix in the initial sample and its modification during and after straining (elongation). The goal is to relate the macroscopic mechanical behaviour with the structure of the aggregate network. The present paper is a qualitative overview of recent results obtained on well defined composites.
Percolation model of hyperbranched polymerization
Authors: Galina Henryk , Lechowicz Jaromir B. , Potoczek Marek 
Published: October 2003

AbstractComputer simulations of the step‐growth homopolymerization of an AB2 monomer have been carried out on a square lattice. No rearrangements of units were made between reaction events. Instead, the capture radius, i.e., the maximum distance between the randomly selected unit and its reaction partner was changed. The reaction was considered as controlled either by diffusion and local concentration fluctuations or by the law of mass action (classical limit). The size distribution of polymer species and the extent of cyclization reactions in the polymerization are discussed.
Interaction of non‐ionic hydrogels with weak aromatic acids
Authors: László Krisztina , Kosik Katalin , Filipcsei Genovéva , Zrínyi Miklós 
Published: October 2003

AbstractMeasurements are reported of the swelling behaviour at 20°C of poly (N isopropylacrylamide) (PNIPA) gels in aqueous solutions of two weak aromatic acids, phenol and resorcinol. For solute concentrations below 45 mmol/l the uptake of these solutions is similar. Due to selective solvation phenol exhibits an excess equilibrium concentration inside the gel of 5% over that in the surrounding bath, while for resorcinol, the excess is found to be 12%. At 50 mmol/l solute concentration, both systems display a volume transition accompanied by expulsion of the solvent. The solubility limits in water of these aromatic compounds, which are significantly different from each other (870 mmol/l and 9080 mmol/l respectively), are far above this critical concentration. In the collapsed condition the expelled liquid spreads on the surface of the phenol treated gel, while an ordered arrangement of separate droplets is generated in the case of resorcinol. In the latter case an acute contact angle was observed. It is also shown by acid‐base titration that the PNIPA/water system may exhibit a slight ion exchanging character.
Evaluation of the degree of cross‐linking of cellulose‐based superabsorbent hydrogels: a comparison between different techniques
Authors: Lionetto Francesca , Sannino Alessandro , Mensitieri Giuseppe , Maffezzoli Alfonso 
Published: October 2003

AbstractThree different techniques have been applied to the evaluation of the degree of cross‐linking of superabsorbent cellulose‐based hydrogels obtained from water solutions of carboxymethylcellulose sodium salt (CMCNa) and hydroxyethylcellulose (HEC), chemically cross‐linked with divinyl sulfone. These polyelectrolyte hydrogels are biodegradable and have the same sorption capacity as acrylate‐based superabsorbents on the market. A 13C solid state NMR analysis was carried out on dry samples of hydrogel to obtain the degree of cross‐linking, an important parameter that affects the swelling and mechanical properties of a hydrogel. Dynamic mechanical analysis was performed during the hydrogel cross‐linking using a parallel plate rheometer under oscillatory deformations in order to monitor the evolution of the hydrogel viscoelastic properties during the synthesis. The value of |G*| and the slope of the stress‐deformation ratio plots from uniaxial compression tests were used to evaluate the elastically effective degree of cross‐linking according to classical rubber elasticity theory. Moreover, a dynamic mechanical analysis was carried out on cross‐linked hydrogels at different degrees of swelling in order to investigate the influence of the swelling on the mechanical properties and the application of rubber elasticity theory to swollen hydrogels.
Thermodynamics of water sorption in acrylic homonetworks and IPNs
Authors: Gallego Ferrer Gloria , Monleón Pradas Manuel , Gómez Ribelles José Luis 
Published: October 2003

AbstractThe equilibrium thermodynamic properties of poly(hydroxyethyl acrylate) and poly(ethyl acrylate)‐i‐poly(hydroxyethyl acrylate) hydrogels are investigated starting from the water sorption isotherms of the systems. Partial enthalpy and entropy of the sorbed water in the gel differ markedly from the values of pure water at the lowest water contents, and tend to those of liquid water as saturation is approached. The residual mixing free energy is calculated, as a means of assessing the intensity of the water‐polymer interaction. Its small positive magnitude shows that water‐polymer hydrogen bonds are labile compared to water‐water and polymer‐polymer hydrogen bonds, and thus the stability of the gel state is still mainly due to the combinatorial entropic contribution to the mixing free energy. An equation correctly describing the sorption isotherms, when combined with the thermodynamic equations, can deliver the true water‐polymer interaction parameter and its dependence on the polymer volume fraction in the gel.
Ion condensation in a polyelectrolyte gel
Authors: Morfin Isabelle , Horkay Ferenc , Basser Peter J. , Bley Françoise , Ehrburger‐Dolle Françoise , Hecht Anne‐Marie , Rochas Cyrille , Geissler Erik 
Published: October 2003

AbstractAnomalous small angle X‐ray scattering is used to determine the distribution of divalent ions in a neutralized polyelectrolyte gel of sodium polyacrylate in the vicinity of the volume transition. At the five different energies of the incident beam used to vary the contrast, the scattering curves have similar shapes, and are separated only by constant multiplying factors. This result, in conjunction with SANS results from the same sample, indicates that the divalent ion (strontium) is confined on the polymer backbone.
Compression elastic modulus of neutral and protonated poly(N‐vinylimidazole) hydrogels
Authors: Valencia Joaquín , Baselga Juan , Pacios Isabel E. , Piérola Inés F. 
Published: October 2003

AbstractThe compression modulus of poly(N‐vinylimidazole) (PVI) hydrogels synthesized by cross‐linking polymerization in aqueous solution, was measured at room temperature in several related systems: i) just after polymerization, ii) swollen at equilibrium in deionized water, iii) swollen in HCl (aq) (pH=2.5), iv) swollen in HCl (pH=2.5) and 1 M NaCl (aq) solution and v) swollen in H2SO4 (pH=2.5) (aq) solution. Samples of the first and second groups are neutral whereas hydrogels of the other three groups are ionic because of protonation of basic imidazole groups. The experimental results were fitted with the Erman‐Monnerie theory, applied to compression measurements for the first time, to determine the phantom modulus, [fph*], and the parameter κG which measures the constraining role of entanglements on the fluctuations of chains between knots.
A Monte Carlo simulation of a knotted linear chain system as an elementary network fragment
Authors: Romiszowski Piotr , Sikorski Andrzej 
Published: October 2003

AbstractWe present the results of the Monte Carlo simulations of the dynamics of the linear chain system. The chains were constructed on a simple cubic lattice. The simulations were carried out by means of the classical Metropolis sampling method with the excluded volume effect present. No other interactions were introduced into the system (athermal polymer case). The linear chains in the system were constructed in such a way that there were knots at certain positions. Also, some chains were threaded through the knots forming the topological constraints in the system. The system under consideration underwent a series of micromodifications during the simulation run. Then the trajectory was analysed and the dynamics of the system was described by means of the autocorrelation functions. The short‐time dynamics enabled us to investigate whether or not the knotted constraints affect the local dynamics of the chains. Also the long‐time dynamics of the system can be useful in the characterizations of the dynamical properties of the fragments of the networks.
Predicting the modulus of end‐linked networks from formation conditions
Authors: Stepto R.F.T. , Cail J.I. , Taylor D.J.R. 
Published: October 2003

AbstractThe application of a Monte‐Carlo (MC) algorithm to account fully for loop formation in RA2 + R′B3 and RA2 + R′B4 polymerizations is described. The resulting interpretation of experimental elastic moduli of HDI‐based polyurethane networks prepared at different dilutions shows it is essential to account for elastic losses in loop structures of all sizes. An important parameter, x, is introduced, namely the average fractional loss of elasticity per larger loop structure relative to the loss per smallest loop structure. Values of x vary between 0.50 and 0.60. Subsequent application of the MC calculations to the formation and resulting structures of MDI‐based polyurethane networks and poly(dimethyl siloxane) networks again predicts significant reductions in modulus due to loop structures. However, comparison with experimental modulus data shows that the reductions in modulus due to loops are outweighed by increases due to chain interactions and to topological entanglements.
Viscoelastic properties of polyacrylonitrile gels: dependence of sol‐gel transition on concentration and aging time
Authors: Tanaka Yutaka 
Published: October 2003

AbstractDynamic viscoelasticity was observed for polyacrylonitrile solution in dimethylacetamide in the process of sol‐gel transition. The gel was prepared by the freezing and thawing method, i.e., the solution was frozen at −50°C and then kept at 25°C so as to undergo gelation. The longer the freezing time, the shorter was the gelation time. Also the higher the concentration, the shorter the gelation time. The strength of the network, S and critical exponent n at the transition point were evaluated. The S value increased with increasing concentration and was constant in value in spite of the variation of freezing time when the concentration of the solution was constant.
Deterministic solutions for a step‐growth polymerization
Authors: Choi Sungjae , Liu Xiangdong , Timm Delmar C. 
Published: October 2003

AbstractChain topology, including branch node, chain link and cross‐link dynamics that contribute to the number of elastically active strands and junctions, are calculated using purely deterministic derivations. Solutions are not coupled to population density distributions. An eigenzeit transformation assists in the conversion of expressions derived by chemical reaction principles from time to conversion space, yielding transport phenomena type expressions where the rate of change in the molar concentrations of branch nodes with respect to conversion is expressed as functions of the fraction of reactive sites on precursors and reactants. Analogies are hypothesized to exist in cross‐linking space that effectively distribute branch nodes with i reacted moieties between cross‐links having j bonds extending to the gel. To obtain solutions, reacted sites on nodes or links with finite chain extensions are examined in terms of stoichiometry associated with covalent bonding. Solutions replicate published results based on Miller and Macosko's recursive procedure and results obtained from truncated weighted sums of population density distributions as suggested by Flory.
Properties of epoxy systems with clay nanoparticles
Authors: Zelenková Mysková Markéta , Zelenka Jiři , Spaček Vladimir , Socha Frantisek 
Published: October 2003

AbstractLow molecular epoxy resin was mixed with different concentrations of montmorillonite clay with alkylamine‐modified surface. The presence of the clay nanoparticles influences the gel time of the amine cured resin as well as the mechanical properties. Toughness and modulus, both in the glass and the rubberlike region, increase with clay concentration. An increasing amount of lower mobility phase with increased clay concentration was observed.
Pyridine and aminide derivatives as ligands in 1 : 1 Rh2[tfa]4 adducts: 1H, 13C and 15N NMR study
Authors: Jaźwiński Jarosław , Duddeck Helmut 
Published: October 2003

Abstract1H, 13C and 15N chemical shifts of some pyridines and mesoionic oxatriazole aminides were recorded in the absence and presence of the complex dirhodium tetrakis(trifluoroacetate). The adduct formation shifts prove that the nitrogen atom in the pyridine derivatives and the N‐6 atom of the aminides are the binding sites in the adducts. At low temperature, adduct species can be identified separately by their individual signals. The 15N chemical shift responds very sensitively even to small concentration changes in the adduct. Copyright © 2003 John Wiley & Sons, Ltd.
The advantages of forward linear prediction over multiple aliasing for obtaining high‐resolution HSQC spectra in systems with extreme spectral crowding
Authors: Reynolds William F. , Enriquez Raul G. 
Published: October 2003

AbstractThe resolution obtained for the highly crowded 13C–1H HSQC spectrum of a mixture of three trisaccharides using forward linear prediction is compared with that recently reported for the same mixture but using multiple (100‐fold or greater) aliasing of HSQC spectra in combination with a computer program to unfold the aliased spectra. It is shown that forward linear prediction gives slightly superior resolution while avoiding the significant sensitivity loss associated with the very narrow spectral windows and consequent long evolution times required for the multiple aliasing method. Copyright © 2003 John Wiley & Sons, Ltd.