bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photodestruction of human dental plaque bacteria: Enhancement of the photodynamic effect by photomechanical waves in an oral biofilm model
Authors: Soukos Nikolaos S. , Mulholland Stephen E. , Socransky Sigmund S. , Doukas Apostolos G. 
Published: August 2003

AbstractBackground and ObjectivesPeriodontal disease results from the accumulation of subgingival bacterial biofilms on tooth surfaces. There is reduced susceptibility of these biofilms to antimicrobials for reasons that are not known. The goals of this study were to investigate the photodynamic effects of a conjugate between the photosensitizer (PS) chlorine6 (ce6) and a poly‐l‐lysine (pL) with five lysine residues on human dental plaque bacteria as well as on biofilms of the oral species Actinomyces naeslundii after their exposure to photomechanical waves (PW) generated by a laser in the presence of the conjugate.Study Design/Materials and MethodsSubgingival plaque samples from 12 patients with chronic destructive periodontitis were divided in 3 groups that were incubated for 5 minutes with 5 μM ce6 equivalent from the pL–ce6 conjugate in the presence of fresh medium (group I), PBS (group II), and 80% PBS/20% ethylenediaminetetra‐acetic acid (EDTA) (group III) and were exposed to red light. Also, biofilms of A. naeslundii (formed on bovine enamel surfaces) were exposed to PW in the presence of 5 μM ce6 equivalent from the pL–ce6 conjugate and were then irradiated with red light. The penetration depth of the conjugate was measured by confocal scanning laser microscopy (CSLM). In both cases, after illumination serial dilutions were prepared and aliquots were spread over the surfaces of blood agar plates. Survival fractions were calculated by counting bacterial colonies.ResultsThe PS/light combination achieved almost 90% killing of human dental plaque species. In biofilms of A. naeslundii, CSLM revealed that PW were sufficient to induce a 50% increase in the penetration depth of the pL–ce6 conjugate into the biofilm. This enabled its destruction (99% killing) after photodynamic therapy (PDT).ConclusionsPW‐assisted photodestruction of dental plaque may be a potentially powerful tool for treatment of chronic destructive periodontal disease. Lasers Surg. Med. 33:161–168, 2003. © 2003 Wiley‐Liss, Inc.
Fiber spinning behavior of a 3‐hydroxybutyrate/3‐hydroxyhexanoate copolymer
Authors: Bond Eric Bryan 
Published: August 2003

AbstractThe fiber spinning behavior of a poly(3‐hydroxyalkanoate) (PHA) copolymer resin containing 11.3 mol% hexanoate copolymer (H11) was studied to determine its usefulness in fiber based applications, such as nonwovens. Monocomponent fibers were spun initially, but it was found they would not solidify in the spinline. Bicomponent (sheath/core) fibers were melt spun using a H11 core and a polylactic acid (PLA), as well as a polyethylene succinate (PES) sheath. The spinning results showed that H11 levels up to 30wt% could be incorporated with stable spinning. The incorporation of H11 was found to be limited due to the slow crystallization kinetics of the H11 in the spinline. The neat and bicomoponent fibers were found to have tensile strengths similar to polypropylene. The PES based fiber compositions were found to have elongation‐at‐break values similar to PP. Neat H11 copolymer fibers were found to be readily biodegradable at 25°C under aerobic conditions.
Thermosetting of wheat protein based bioplastics: modeling of mechanism and material properties
Authors: Domenek Sandra , Morel Marie‐Hélène , Redl Andreas , Guilbert Stéphane 
Published: August 2003

AbstractStructural investigation of gluten‐glycerol blends subjected to heat‐treatment was carried out by size‐exclusion high performance liquid chromatography (SEC) and stress‐strain tests. SEC is a valuable tool to investigate the size distribution of gluten protein chains, while the molecular weight between network junctions (Me) can be estimated from the elastic plateau modulus. Wheat gluten aggregation upon thermosetting seems to proceed through direct covalent cross‐linking between glutenin oligomers and the gluten macropolymer. The time course of the reaction, which showed a slow‐down of the reaction rate with time, was described by a simple mechanistic model. The deceleration of the reaction rate was presumably due to the development of a three‐dimensional protein network, which decreased the accessibility of reactive groups. The network formation could be evidenced separately by the decrease of Me during the heat‐treatment.
The performance of degradable polymer bags
Authors: Davis Georgina , Bulson Hugh , Harrison David , Billett Eric 
Published: August 2003

AbstractThe use of degradable polymers for the collection and composting of organic wastes is explored within this paper. With reference to one trial where the performance of a ‘degradable’ polyethylene based sack for the kerbside collection of organic wastes was investigated. Areas for consideration were the impacts of the degradable polymer on the composting process and the quality of the finished product. This trial also included a comparative study of two different types of ‘degradable’ polymer sacks currently on the European market (polyethylene and starch). A number of quantitative tests were conducted on the different polymers to assess the mechanisms of degradation and how this affected their suitability for the treatment of organic wastes. Provisional results have indicated that the polyethylene (PE) sacks are not degrading as anticipated within open windrow conditions, adversely affecting both the composting process and the quality of the finished compost product. Whilst the degradable starch based sacks appear to actively degrade within open windrow compost conditions.
Solubility islands for polymer blends – a new option to homogenize incompatible polymers?
Authors: Imre Attila R. 
Published: August 2003

AbstractExperimental results of liquid‐liquid phase equilibrium in a polydisperse blend of two polyalkylsiloxane are presented here. The UCST has an unusual pressure dependence: pressure induced miscibility at moderate pressures and pressure induced immiscibility at higher pressures, above a double critical point. The cloud point curve has two maxima in (concentration, temperature) as well as in (concentration, pressure) space. Approaching the double critical point, the high and low pressure branches of the cloud point curve merge and in a certain stage of this merging, they form a miscibility island located inside the two‐phase region. Islands of this kind can give us a new tool to mix virtually immiscible blends.
Rheo‐optical determination of the interfacial tension in a dispersed blend
Authors: Tassieri Manlio , Grizzuti Nino , Greco Francesco 
Published: August 2003

AbstractIn this work, we present two novel methods to determine the interfacial tension of a disperse polymer blend through rheo‐optical measurements of flow‐induced single drop distortions. A counter‐rotating shearing device with transparent plates is used to measure drop distortions. The cell geometry allows for a top view of the deforming drop, i.e., along the velocity gradient direction. Such a view is the only possible option for all currently available commercial rheo‐optical instruments. Two different quantities are monitored, namely, the drop axis along the vorticity direction, and the rotation period of the drop surface. We use drops of a polyacrilamide aqueous solution (a shear thinning liquid) immersed in a polyisobutene matrix. Experimental results are interpreted in terms of theories for Newtonian liquids, where the relevant parameter is the Capillary number. If an appropriate viscosity ratio is chosen, that accounts for the shear thinning behaviour of the drop phase, good agreement is found between measurements and theoretical predictions. As a result, a robust estimate of the blend interfacial tension, that makes use only of the information acquired from top view experiments, is obtained.
Blends of an epoxy thermosetting polymer with aromatic liquid‐crystalline polyesters
Authors: Jasinski Wojciech , Carlier Véronique , Legras Roger , Mormann Werner 
Published: August 2003

AbstractA series of aromatic liquid‐crystalline polyesters with different composition have been synthesized to adjust transition temperatures and molecular weight. Miscibility of polyesters with bisphenol‐A‐diglycidyl ether (DEGBA), 4,4′‐methylene‐bis(3‐chloro‐2,6‐dimethylaniline) (MCDEA) and the influence on transition temperatures has been studied. Miscibility of binary and ternary mixtures was found over the whole range of composition depending on the temperature. Thermoset formation by curing of LC‐polyester / DEGBA / MCDEA mixtures containing different amounts of polyester resulted in reaction‐induced phase separation with polyester content from 30 to 50 wt.%. Cloud point techniques, scanning electron microscopy (SEM) and dynamic mechanical thermal analysis (DMTA) have been applied.
An investigation of sPS/epoxy blends by means of x‐ray scattering techniques
Authors: Zafeiropoulos N.E. , Schut J. , Pohlers A. , Stamm M. , Gerard J.‐F. 
Published: August 2003

AbstractSPS is a fast crystallisable polymer that possesses a number of interesting properties due to its semicrystalline nature. However, one major problem is the necessity of applying high temperature for processing sPS (above 290°C), as its melting point is approximately 270°C, and its degradation threshold is at 310‐320°C A possible solution to the processing problem may be blending of the sPS with another polymer to lower the viscosity, and subsequently, the processing temperature. SPS, however, exhibits polymorphism like many other semicrystalline polymers. Due to its polymorphism it is necessary to investigate the crystallisation of sPS in sPS blends. Such an investigation is conducted in the present study for the system sPS/epoxy by means of x‐ray scattering techniques. The results from WAXS revealed that the degree of crystallinity increases by decreasing the sPS content in the sPS/DGEBA blends. Investigations by means of SAXS revealed a trend of increasing the long period by decreasing the sPS content in the blends.
In situ monitoring of reaction‐induced phase separation with modulated temperature DSC
Authors: Swier Steven , Van Mele Bruno 
Published: August 2003

AbstractA linearly polymerizing and network forming epoxy‐amine system, DGEBA‐aniline and DGEBA‐MDA, respectively, will be modified with 20 wt% and 50 wt% of a high‐Tg thermoplastic poly(ether sulphone) (Tg=223°C), respectively, both showing LCST‐type demixing behavior. Reaction‐induced phase separation (RIPS) in these modified systems is studied using Modulated Temperature DSC (MTDSC) as an in situ tool. Phase separation in the linear system can be probed by vitrification of the PES‐rich phase, occurring at a higher conversion than the actual cloud point from light scattering measurements. The negative slope of the cloud point curve in a temperature‐conversion‐transformation diagram unambiguously shows the LCST‐type demixing behavior of this system, while the relation between the composition/glass transition of the PES‐rich phase and the cure temperature is responsible for the positive slope of its vitrification line. Phase separation in the network forming system appears as reactivity increases at the cloud point due to the concentration of reactive groups. Different mixture compositions alter the ratio between the rate of phase separation and the rate of reaction, greatly affecting the morphology. Information about this in situ developed structure can be obtained from the heat capacity evolutions in non‐isothermal post‐cures.
Phase separation in a poly(ether sulfone) modified epoxy‐amine system studied by temperature modulated differential scanning calorimetry and dielectric relaxation spectroscopy
Authors: Montserrat S. , Roman F. , Basany M. , Colomer P. 
Published: August 2003

AbstractThe phase separation induced by the curing reaction of an epoxy based on diglycidylether of bisphenol A (DGEBA) with methylene dianiline (MDA) modified with poly(ether sulfone) (PES) at a concentration of 20 wt% was studied by temperature modulated differential scanning calorimetry (TMDSC) and dielectric relaxation spectroscopy (DRS). The effect of phase separation on the curing kinetics and vitrification phenomena is analysed. The dependence of the log of the measuring frequency on the degree of conversion allows the correlation between the dipolar relaxation of each phase and the vitrification observed by TMDSC to be established.
Bulk and surface properties of blends with semifluorinated polymers and block copolymers
Authors: Pospiech Doris , Häußler Liane , Jehnichen Dieter , Kollig Wolfram , Eckstein Kathrin , Grundke Karina 
Published: August 2003

AbstractThe goal of the investigation presented here is the development of extremely hydrophobic materials based on polysulfone that can be applied, for instance, as fouling‐resistant membrane materials. The concept used is the addition of semifluorinated polymers to polysulfone in suitable blend compositions. The influence of molecular parameters like chain structure of the semifluorinated polymer (segmented block copolymers, random copolymers) and segment molecular weight on the state of phase separation in the bulk and its influence on the surface properties have been systematically examined. It could be shown that segmented block copolymers with semifluorinated polyester segments with intermediate segment molecular weight are more suitable in blends with polysulfone than random polysulfone copolymers having semifluorinated side chains with respect to form homogeneous thin films (coatings) with highly non‐wetting properties.
Multivariate Composition Distribution in Free‐Radical Multicomponent Polymerization, 1
Authors: Tobita Hidetaka 
Published: August 2003

AbstractStatistical multicomponent polymerization is a typical example of a Markovian process for which the generating function approach can be applied. Up to the present, generating functions have been used mainly to obtain analytical solutions. However, recent advances of computer software capable of handling symbolic calculations can throw new light on the old mathematical technique. After formulating the equations representing the instantaneous composition distribution of polymers for a given chain length, r, the illustrative numerical calculations are conducted by using the symbolic calculator. For a multicomponent polymerization consisting of more than two components, the second component distribution is dependent on the composition of the first component (F1), which is represented by the conditional probability given r and F1, $Comp\left( {F_2 \left| {F_1 ,r} \right.} \right)$. It is found that $Comp\left( {F_2 \left| {F_1 ,r} \right.} \right)$ is well approximated by the Gaussian distribution with the variance following the relationship, $r\sigma _{2;1,r}^2 = A + B/r$, as in the case of the first component distribution $Comp\left( {F_1 \left| r \right.} \right)$, where A and B are the constants. With the knowledge of chain length distribution, it is now possible to conduct the full analysis of multivariate distribution of chain length and compositions for multicomponent free‐radical polymerization.Bivariate distribution of composition F1 and F2 for chain length r = 100 in a three‐component system.imageBivariate distribution of composition F1 and F2 for chain length r = 100 in a three‐component system.
Multivariate Composition Distribution in Free‐Radical Multicomponent Polymerization, 2
Authors: Tobita Hidetaka 
Published: August 2003

AbstractA shortcut approximate method is proposed for determining the multivariate composition distribution. It is found that the multivariate normal distribution can represent the major body of composition distribution for long chains reasonably well. The covariance of the multivariate composition distribution is obtained from the generating function proposed in Part 1 of this series. The covariance vij changes with chain length r, however a simple relationship, rvij = A + B/r, is found to exist, where A and B are the constants. These constants can be determined from the vij values for rather small values of r, which reduces the required amount of calculation significantly, and the multivariate composition distribution for long chains can be estimated conveniently.Contour plot of the bivariate composition distribution for the three‐component system with r = 100. The solid curves are the exact solution, while the dotted curve is the approximation using the multivariate normal distribution.imageContour plot of the bivariate composition distribution for the three‐component system with r = 100. The solid curves are the exact solution, while the dotted curve is the approximation using the multivariate normal distribution.
Monte Carlo Study of Heteroarm Star Copolymers in Good and Selective Solvents
Authors: Havránková Jitka , Limpouchová Zuzana , Procházka Karel 
Published: August 2003

AbstractLattice Monte Carlo simulations of conformations of hereroarm star copolymers AnBnin selective solvents were performed using a special variant of the Siepman and Frenkel algorithm. The effects of solvent quality, the number and lengths of blocks on the collapse of the insoluble block A, segregation of the two types of blocks and the behavior of the soluble blocks B were studied mainly for “hairy” stars containing high numbers of long arms. The simulation shows that insoluble blocks collapse in strongly selective solvents and the gravity centers of soluble and insoluble blocks separate which suggests the possibility of the formation of non‐spherical structures.Snapshots of star a in a very bad solvent (T = 3.00) for blocks A. There are two different views of the star with a total number of armsf = 16 and number of segmentsN = 300.imageSnapshots of star a in a very bad solvent (T = 3.00) for blocks A. There are two different views of the star with a total number of armsf = 16 and number of segmentsN = 300.
Simulations of Electric Field Induced Lamellar Alignment in Block Copolymers in the Presence of Selective Electrodes
Authors: Kyrylyuk A. V. , Sevink G. J. A. , Zvelindovsky A. V. , Fraaije J. G. E. M. 
Published: August 2003

AbstractComputer simulations have been performed for electric field induced parallel‐perpendicular lamellar phase transition in the presence of electrodes. The simulations are based on the dynamic density functional theory. Here we provide the extension of earlier work in two dimensions (2D) to three dimensions (3D). The result is a vivid picture of the transitions through defect creation and collision.Observed change in lamellar alignment with applied electric field.imageObserved change in lamellar alignment with applied electric field.
“Volume‐Preserving” Conformational Rheological Models for Multi‐Component Miscible Polymer Blends Using the GENERIC Formalism
Authors: Eslami Hassan , Ramazani Ahmad , Khonakdar Hossein Ali 
Published: August 2003

AbstractA family of conformational rheological models for multi‐component miscible polymer blends is developed using a modified form of the Poisson bracket formulation. Two conformation tensors called c1 and c2 are introduced to show the orientation of the first and the second components of a blend, respectively. The mobility tensor and the energy function for each blend component are expressed in terms of these conformation tensors. The interaction effects are also included by energy expressions. The predictions of this family of “volume‐preserving” models are illustrated for a Hookean‐type energy function and several expressions of the modified mobility tensors. The results are illustrated for material functions in transient (start‐up and relaxation) and steady shear flows. The predictions are compared with experimental data taken from the literature for a miscible polymer blend. Study of the model sensitivity to its parameter shows that model predictions can cover a wide range of rheological behavior generally observed for multi‐component miscible polymer blends in steady and transient shear flows.Experimental data and model predictions for steady shear viscosity for HDPE/LDPE blends.imageExperimental data and model predictions for steady shear viscosity for HDPE/LDPE blends.
A Conditional Monte Carlo Method to Determine the Architectures of Metallocene Catalyzed Polyethylene
Authors: Hoefsloot Huub C. J. , Iedema Piet D. 
Published: August 2003

AbstractTwo polymer molecules of the same length (n) and the same number of branch points (N) can have different properties, since they may possess distinct architectures. In this paper we present a conditional Monte Carlo algorithm for the virtual synthesis of metallocene‐catalyzed polyethylene (PE) in a continuous stirred tank reactor (CSTR). The condition for the Monte Carlo method consists of a fixed chain length distribution (CLD) and a degree of branching distribution (DBD). These distributions are calculated with a Galerkin finite element method. The synthesis method is a recursive algorithm that subsequently creates insertions of sub‐structures containing numbers of branch points according to a certain probability density function. This provides an adjacency matrix describing the connectivity between the branch points, while separately a vector containing the length of segments between branch points and terminal segments is generated. Characterization of the architectures proceeds by rheological features, seniorities and priorities, and molecular properties like the radius of gyration. Comparing the radii of gyration of metallocene polyethylene and low density PE (ldPE) shows the former to possess a more comb‐like structure on average. This is confirmed by the rheological characterization. The found bivariate seniority/priority distribution agrees well to the results of an analytical study of the same chemical system.Constituting elements of the algorithm.imageConstituting elements of the algorithm.
Interfacial Properties of Asymmetric Polymer Mixtures
Authors: Adhikari Narayan P. , Straube Ekkehard 
Published: August 2003

AbstractUsing a Monte‐Carlo simulation of a continuous space Rod Bead Model the interface properties of systems of flexible polymer chains with different sizes of monomers are investigated. An immiscible polymer blend in the strong segregation state is modeled by a double sandwich system of chains differing by an factor of two in the size of the beads and the interfacial tension is calculated by a virial theorem method. The simulation data are compared to self‐consistent mean field and experimental data. The results show that the simulation data agree very satisfactory with mean‐field results. The interfacial tension decreases for asymmetric systems in comparison to symmetric systems with comparable volume contents of monomers and interaction strengths due to a decrease of the effective interaction. The parameters of the investigated systems are close to the properties of PS, PMMA and PI melts. A comparison with experimental results yields a very good agreement with data for PS/PMMA and less satisfactory for PS/PI. Additionally to the interfacial tension we have studied the interfacial width, the deformation of polymer chains near the interface, distributions of chain ends, monomer densities and distributions of centers of mass of chains.Snapshot of a typical configuration for chains with different monomer sizes and equal number of monomers per chain.imageSnapshot of a typical configuration for chains with different monomer sizes and equal number of monomers per chain.