bluuebunny/crossref_metadata_2025_split huggingface dataset:
Compound formation and solvent (dis)ordering in syndiotactic polystyrene/benzylmethacrylate systems
Authors: Goossens Han , Rastogi Sanjay , Lemstra Piet 
Published: March 2011

AbstractIn‐situ small‐ and wide‐angle X‐ray scattering (SAXS and WAXS) experiments combined with Raman spectroscopy have been performed to study the phase behaviour of syndiotactic polystyrene (sPS) and benzylmethacrylate (BzMA). In the quenched gels, sPS adopts a helical conformation which is stabilised by the solvent molecules, in fact compound formation occurs. From the combined experimental data it was concluded that two different structural modifications exist within the solvent‐included helical δ‐phase, respectively the δ' phase in which the solvent molecules are intercalated and ordered between the phenyl rings of sPS and a δ” phase where this solvent ordering is lost.
A Study on the ordering of intercalated solvents in poly‐benzyl‐l‐glutamate; In‐situ raman and X‐ray scattering investigations
Authors: Corstjens Tosca , Rastogi Sanjay , Lemstra Piet 
Published: March 2011

AbstractA polymer/solvent system can form a gel due to specific interactions between the polymer and the solvent. For poly‐benzyl‐L‐glutamate/solvent systems, gelation can be based on carbonyl or phenyl ring interactions, depending on the solvent. The present paper describes X‐ray scattering and Raman investigations on cast films of poly‐benzyl‐L‐glutamate (PBLG) and benzylmethacrylate (BzMA). The studies indicate that in the cast samples separate zones of PBLG and BzMA are present. Upon heating, the system homogenises and the PBLG molecules pack in a pseudo hexagonal lattice. At approximately 150°C a new reflection at 11.4 Å in the WAXS pattern arises. This reflection is attributed to structural ordering of the solvent, due to intercalation of the solvent molecules within the helices of PBLG. The observed changes in the WAXS pattern upon heating are supported by Raman experiments.
Polymer‐solvent interactions in thermoreversible gels of isotactic poly(methyl methacrylate) as studied by measurement of 1h NMR relaxation of the solvent
Authors: Spêváček Jiři , Brus Jiři 
Published: March 2011

AbstractDynamic structure and polymer‐solvent interactions in solutions and gels of isotactic (i) poly(methyl methacrylate) (PMMA) in butyl acetate (BAC) were characterized by measurements of nonselective and selective 1H NMR spin‐lattice relaxation times of the solvent. In thermoreversible gels, the existence of i‐PMMA‐BAC complex, where the life‐time of the bound solvent is − 100 ms or shorter, was confirmed. Although the correlation time of the solvent bound in i‐PMMA‐BAC complex is 5‐10 times longer than for the free solvent, there is still a relative motional freedom for complexed solvent molecules. The same behaviour observed recently for thermoreversible gels of syndiotactic PMMA indicates the same character of polymer‐solvent complexes in gels of both stereoregular forms of PMMA.
Scattering properties of agarose gels
Authors: Rochas Cyrille , Hecht Anne‐Marie , Geissler Erik 
Published: March 2011

AbstractStatic light scattering and small angle neutron scattering measurements are reported for agarose hydrogels prepared under various conditions of concentration and temperature. For the wide range of transfer wave vector explored, these measurements show that the gels do not display fractal behaviour. Their structure is better described by a stretched exponential form, in which the value of the exponent is n = 0.2.As found by other authors, a maximum in the scattering intensity is observed in the light scattering spectra. The position of the maximum, qmax, depends on the concentration and on the thermal history of the sample. The inverse length 1/qmax is in good agreement with published measurements of the pore size D in this system.Preliminary measurements by small angle scattering indicate that the sol‐gel transition is not of spinodal type.
Structural and thermodynamic features of the polyhydroxybutyrate physical gels
Authors: Cesàro Attilio , Fabri Deborah , Sussich Fabiana , Paradossi Gaio 
Published: March 2011

AbstractThe structural and thermal properties of polyhydroxybutyrate (PHB) gels in dimethylformamide (DMF) are presented and discussed. The dilute and semi‐dilute mixed PHB/DMF system undergoes a phase separation on cooling at a temperature Tgel, producing a gel in which the crystalline fraction is of the order of 50‐60% and the diffraction pattern is that of disperse nano‐crystals, with the same unit cell of the pure crystalline PHB. Upon heating, two melting peaks are normally observed at Tm1 and Tm2 (always higher than Tgel). Shapes of the peaks, temperatures and enthalpies of melting depend slightly on scanning rate on heating but on the procedure of gel preparation. Reproducibility and reversibility have always been found with repeated thermal cycles. A thermodynamic phase diagram is therefore constructed and discussed, although the morphology of the system may be subject to the experimental conditions under which the gel is prepared.
The mutual effect of absorption of biologically active substances and microstructure of native cellulose matrix on the properties of resulting compounds
Authors: Kotelnikova N. E. , Panarin E. F. , Serimaa R. , Paakkari T. , Wegener G. , Windeisen E. 
Published: March 2011

AbstractIn order to obtain multicomponent polymer systems exhibiting biological activity microcrystalline cellulose was used as a matrix for biologically active compounds, such as dimethylbenzylalkylammonium chloride, poly‐N‐vinylpyrrolidone, copolymer of N‐vinylpyrrolidone and crotonic acid, and complex of dimethylbenzylalkylammonium chloride with copolymer of N‐vinylpyrrolidone and crotonic acid. Adsorption interaction of microcrystalline cellulose with these was studied under various conditions. Adsorption isotherms of compounds of polymer nature are of similar character and are described by the Freundlich equation. The isotherms of dimethylbenzylalkylammonium chloride are described by the Langmuir equation. Characteristics of the resulting compounds were obtained using XPS and IR Fourier spectroscopy, WAXS, and SEM. Chemical interaction between microcrystalline cellulose and dimethylbenzylalkylammonium chloride takes place. This interaction leads to a new labile morphological cellulose structure accessible to penetration, which is confirmed at a morphological level by SEM.
Correlations between mark‐houwink‐sakurada parameters for linear and star‐like polymers
Authors: Ioan Catalina , Ioan Silvia , Simionescu Bogdan C. 
Published: March 2011

AbstractThe influence of the excluded volume on the intrinsic viscosity of linear and star‐like polymers in dilute solution is reflected on the Mark‐Houwink‐Sakurada (MHS) parameters k and “a”. A correlation between these parameters and the number of arms for star‐like polybutadiene in different solvents is proposed. Also, for various linear polymers, a relation describing the decrease of parameter k with increasing “a”, the proportionality coefficient being the unperturbed parameter kθ, is established.
Structural study of hyaluronic acid oligomers and their complexes with copper in water by NMR and IR and molecular dynamics calculations
Authors: Marchettini Nadia , Barbucci Rolando , Bonechi Claudia , Donati Alessandro , Magnani Agnese , Niccolucci Valentina , Tiezzi Enzo 
Published: March 2011

AbstractThe hexasaccharide (trimer) and tetrasaccharide (dimer) oligomers of hyaluronic acid were investigated by 1H and 13C high resolution Nuclear Magnetic Resonance. The dynamic behavior of the molecules and their complexation with copper(II) were analysed by 1H NMR relaxation studies. A specific site for the complexation of the tetrasaccharide with Cu2+ was demonstrated by analysis of the paramagnetic effect of the metal on non‐selective proton relaxation rates. A model for the complex involving two molecules of the tetrasaccharide is proposed.
Studies of the γ ← α transition in syndiotactic polystyrene
Authors: Naddeo Carlo , Guadagno Liberata , Acierno Domenico , Vittoria Vittoria 
Published: March 2011

AbstractIn this work we compare calorimetric and X‐ray diffraction experiments realized on annealed sPS in helical γ forms resulting by different treatements: From clathrate δ form and from interaction of amorphous sample with acetone. The experimental results show that the γ form obtained by acetone converts into the more ordered final α” form modification; while the γ form, obtained by thermal treatments of δ form, transforms into the poorly ordered final α' form.
The rate of solvent diffusion in amorphous polymers
Authors: Vesely D. 
Published: March 2011

AbstractThe present work is a contribution to our understanding of one aspect of the diffusion process, the diffusion rate. It attempts to show that all diffusion theories must satisfy the following:1) the rate of diffusion at the initial stages of the process must be finite2) the rate of diffusion must have square root time dependence at longer diffusion distances.Deviations of experimental data from these rules usually result from experimental inaccuracies. Whereas Fickian approach satisfies the second but not the first rule and Case II sorption the opposite, their combination satisfies neither. Two alternative explanations, which provide a very good correlation with the experimental data, are suggested: Limited diffusion rate and sorption kinetics.
Functionalization of a polyaspartamide with glycidyl methacrylate: A useful method to prepare hydrogels through gamma irradiation
Authors: Giammona Gaetano , Pitarresi Giovanna , Cavallaro Gennara , Spadaro Giuseppe 
Published: March 2011

Abstractα,β‐Poly(N‐2‐hydroxyethyl)‐DL‐aspartamide (PHEA) was derivatized with glycidyl methacrylate (GMA). Aqueous solutions of the obtained copolymer PHEA‐GMA (PHG) were irradiated by gamma rays with a dose rate of 0.5 KGy/h and at zero°C in the presence or in the absence of N, N'‐methylenebisacrylamide (BIS). New hydrogel systems were obtained and characterized by FT‐IR analyses and swelling measurements in aqueous medium at different pH values.
Transport properties of an hydrophobic‐hydrophilic copolymer
Authors: Gorrasi G. , Vittoria V. 
Published: March 2011

AbstractSorption and diffusion properties of a copolymer composed by hydrophilic and hydrophobic blocks have been analyzed. The material, obtained as a film by moulding the powders under pressure, was submitted to thermal treatments, and the structural organization of the samples was investigated using water vapour and dichloromethane as permeants. The polar solvent (water) has been useful to investigate the hydrophilic amorphous regions, while the apolar one (methylene chloride) gave information about the organization of the hydrophobic amorphous phases.
Interfacial phenomena, adhesion and macroscopic properties in polymer composites
Authors: Pegoraro M. , Di Landro L. , Severini F. 
Published: March 2011

AbstractThe microfragmentation or the single‐fiber composite method for the evaluation of fiber‐matrix adhesion in polymer composites is presented emphasizing advantages and drawbacks. The improvements of the methods introduced in recent years (laser Raman spectroscopy, optical examination of interfacial region, estimation of the stress state at the interface, consideration of viscoelastic properties of the matrix) to obtain more detailed information on the interface failure mechanisms are described. A modified method with a coaxial geometry, which extends the applicability of the test to brittle matrices, is shown. A number of experimental results obtained both with thermoplastic and thermoset matrices containing carbon and glass fibers is reported. Chemical modifications of carbon fiber surfaces were carried out, which effectively changed the adhesion to the high‐performance bismaleimide matrix. In particular, the treatment with ammonia is shown to be promising for improvement of adhesion in graphite/bismaleimide composites.
Collective dynamics of terminally anchored polymer chains
Authors: Anastasiadis Spiros H. 
Published: March 2011

AbstractThermal fluctuations of the segment density profile of a polymer brush were probed by dynamic light scattering in the evanescent wave configuration; the time correlation functions of concentration fluctuations with wavevector q were measured. It is found that there is a preferred wavelength of the order of the brush thickness, L0, of these fluctuations with a concurrent slowing down of their thermal decay rate. A theory is presented for the small‐amplitude deformation of the free surface of a parabolic brush in solution; a maximum in the respective structure factor of the concentration fluctuations is predicted at q* L0 ∼ O(1), in agreement with the experiment.
Wetting reversal transition in phase‐separated polymer mixtures
Authors: Genzer Jan , Heier Jakob , Kramer Edward J. 
Published: March 2011

AbstractWe investigate a wetting reversal transition in thin films of two‐phase mixtures of poly(ethylene‐propylene) (PEP) and its deuterated analogue (dPEP) on a substrate covered by a self‐assembled monolayer (SAM) whose surface energy, γSAM, is tuned by varying the SAM composition. As γSAM increases from 21 to 24 mJ/m2, a transition from a three‐layer (air/dPEP/PEP/dPEP/SAM) to a two‐layer (air/dPEP/PEP/SAM) structure occurs at increasing Tc ‐ T, where Tc and T are the critical and transition temperatures, respectively. As the system structure changes from three‐layer to two‐layer, the thicknesses of the dPEP‐rich wetting layers at the air/mixture and mixture/SAM interfaces are found to smoothly increase and decrease, respectively, while the thickness of the PEP‐rich layer (ca. one half of the total film thickness) does not change. The dependence of the transition temperature on γSAM is predicted by a simple model using the experimental data on the surface energies of PEP/dPEP and estimates of the interfacial energy between PEP and dPEP.
Interfacial tension between polymer‐containing liquids — Predictability and influences of additives
Authors: Wolf B. A. 
Published: March 2011

AbstractThe first part of the contribution deals with the interfacial tension, σ, of phase‐separated polymer solutions in single or mixed solvents and of binary polymer blends as a function of the relative distance to the critical temperature of the system, special attention being paid to the possibilities of theoretical prediction. Two methods are discussed in more detail. One is based on a realistic description of the Gibbs energy of mixing as a function of composition, the second correlates σ with the length of the measured tie line. The second part is devoted to another aspect, namely the effects of additives on the interfacial tension between the coexisting phases of demixed polymer solutions and between highly incompatible polymers. In the former case, it is demonstrated that an addition of a thermodynamically good solvent is normally associated with a reduction in σ; however, adding a high‐molecular‐weight compound which is incompatible with the dissolved polymer leads to an increase in σ. The interfacial tension between incompatible homopolymers is efficiently reduced by block copolymers consisting of monomeric units which are either identical with or different from those of the homopolymers; in contrast to theoretical expectation, the molecular architecture of the additives seems to be of minor importance only. Random copolymers which are insoluble in the homopolymers can also efficiently reduce the interfacial tension.
Silane treatment in polypropylene composites: Adsorption and coupling
Authors: Pukánszky Béla , Demjén Zoltán 
Published: March 2011

AbstractThe study of the effect of eight silane coupling agents on mechanical properties of PP/CaCO3 composites showed that the application of certain compounds leads to the reactive coupling of the components. The adsorption of the silanes on the surface of the filler was studied by a dissolution method, while the structure of the adsorbed layer was determined by FTIR spectroscopy and GPC measurements. Model reactions and an FTIR study were carried out to reveal possible coupling reactions of PP and the active silanes. The results showed that amino‐functional silane coupling agents adsorb on the surface of the filler, polycondensation taking place and a polysiloxane layer of high molecular weight forms as a result. The model reactions indicated that during processing, PP oxidizes even in the presence of stabilizers and oxygen‐containing functional groups form on the polymer chains. These easily react with the amino functionality of the silane coupling agents strongly bonding the polymer to the treated filler.
Expolysaccharides from lactic acid bacteria: Technological bottlenecks and practical solutions
Authors: De Vuyst Luc , Degeest Bart 
Published: March 2011

AbstractMicrobial exopolysaccharides are added to or occur in a wide variety of food products, where they serve as viscosifying or gelling agents. Exopolysaccharides with different composition, size and structure are synthesized by several strains of lactic acid bacteria. Structural analyses combined with rheological studies reveal that there is considerable variation among the different exopolysaccharides; some of them exhibit remarkable thickening and shear‐thinning properties and display high intrinsic viscosities. Hence, several slime‐producing lactic acid bacterium strains and their biopolymers have interesting functional and technological properties, which may be exploited towards different products. However, the production of exopolysaccharides from lactic acid bacteria is low and often unstable, and their downstream processing is difficult. Strain improvement, enhanced productivities and advanced modification and production processes (both enzyme and fermentation technology) may contribute to their economic soundness.
Process characteristics of exopolysaccharide production by streptococcus thermophilus
Authors: Degeest Bart , van De Ven Sven , De Vuyst Luc 
Published: March 2011

AbstractThe kinetics of growth and exopolysaccharide (EPS) production from Streptococcus thermophilus were studied and optimized for different physical (temperature, pH, aeration rate) and chemical (carbon/nitrogen ratio) factors in milk medium. From these experiments, it was clear that EPS production displays primary metabolite kinetics. Using the optimized conditions, EPS production could also be established in de Man Rogosa Sharpe medium. Growth‐associated EPS production, bacterial growth and other fermentation data were translated into a mathematical model.
The “food polymer science” approach to flour functionality and ingredient technology in biscuit baking
Authors: Levine Harry , Slade Louise 
Published: March 2011

AbstractAn overview is made on the “food polymer science” approach developed by the authors. The quality and performance of flours for the production of cookies and crackers have been shown to depend upon the major functional polymeric components of flour: gluten protein, damaged starch, and pentosans. Of these, damaged starch and soluble pentosans in soft‐wheat flours are detrimental to the commercial production of low‐moisture cookies and crackers. The detrimental effects of soluble pentosans in flours can be eliminated through the use of pentosanase enzyme in cookie and cracker doughs. Three commercialized applications of this industrial enzyme technology have been patented by Nabisco. The “food polymer science” approach to baking technology has also been used to study finished‐product attributes such as texture, in the context of the thermomechanical properties (e.g. modulus) of glassy solid and rubbery liquid matrices. Results of various studies have clearly demonstrated that products in a glassy solid physical state (at T < Tg) are hard and crisp in texture, but upon increasing plasticization by water (such that Tg is depressed below the observation T), are transformed to a rubbery or viscous liquid state, wherein textural hardness (and mechanical modulus) and crispness are dramatically reduced.
Pectin‐based biodegradable water insoluble films
Authors: Pavlath Attila E. , Voisin Alexandre , Robertson George H. 
Published: March 2011

AbstractAqueous solutions of pectin, an acidic polysaccharide which occurs in various natural products, was cast into clear films. While the films were flexible enough to be used as wrapping materials, their strength and resistance to water were inferior to presently used commercial films. However, precast films immersed into aqueous solutions of multivalent cations became insoluble in water and depending on the ions became stronger in tension. Tensile strength increased to levels comparable to, or in the case of calcium, copper(II) and zinc, greater than those of some commercial wrapping materials
Effect of genetic polymorphism on the gelation of β‐lactoglobulin
Authors: Foegeding E. Allen , Lowe Ruth , Boland Mike J. , Hill Jeremy P. 
Published: March 2011

AbstractThe rheological properties of heat‐induced gels made from β‐lactoglobulin variants A, B and C were compared. The relative G' values (elastic moduli) for gels formed in 90 mM NaCl solutions were A = B > C. Conversely, in 30 mM CaCl2 the relative G' values were C > A = B. The differences in rheological properties were due to A and B variants forming less rigid gels in CaCl2 (∼ 7 kPa) than NaCl (∼ 20 kPa), and variant C forming gels of similar rigidity in both salt solutions. It was concluded that genetic variation in β‐lactoglobulin changes the effect of salts on gelation but does not cause a universal increase or decrease in gel forming ability.
Compositional heterogeneity in pectic polysaccharides: NMR studies and statistical analysis
Authors: Neiss Thomas G. , Cheng H. N. , Daas Piet J. H. , Schols Henk A. 
Published: March 2011

AbstractPectins are a class of heterogeneous polysaccharides used in the food industry as a result of their ability to form gels. They are primarily composed of a (1ŕ4)‐α‐D‐galactopyranosyluronic acid backbone where the carboxylic acid group is methyl esterified at a level which depends on the source of the pectin and processing conditions used to isolate the material. Of considerable interest is the distribution of the free acid and methyl ester groups along this polymer chain. NMR spectroscopy, coupled with statistical analysis, is a powerful technique for the study of sequence distribution of monomers. Experimental conditions (temperature, pD) are reported which are appropriate for the analysis of pectic polysaccharides. Results are presented from a study of sequence distribution in native, modified, and fractionated pectins using 1H and 13C solution NMR methods. The triad sequence information was examined using Bernoullian and Markovian probability models in conjunction with continuous Gaussian distribution and discrete models. Intermolecular heterogeneity in pectins results in triad frequencies which reflect the distribution of acid and ester monomers for native and base saponified pectins. Fractionation of pectin through physicochemical methods and subsequent spectroscopic analysis provide insight into this heterogeneity. Segregation into discrete polymer populations shows a structural diversity best approximated by a 3‐component statistical model.