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Polymer Solutions (polymer + solution)
Selected AbstractsPhotoinduced Shuttling Dynamics of Rotaxanes in Viscous Polymer SolutionsADVANCED FUNCTIONAL MATERIALS, Issue 21 2009Dhiredj C. Jagesar Abstract The effect of external friction, caused by medium viscosity, on the photoinduced translational motion in a rotaxane-based molecular shuttle 1 is investigated. The shuttle is successfully operated in solutions of poly(methacrylonitrile) (PMAN) of different molecular weights in MeCN and PrCN. The viscosity of the medium is tuned by changing the PMAN concentration. The rheological behavior of the polymer solution gives insight into the structure of the polymer solution on the microscopic scale. In PrCN, the entanglement regime is reached at lower concentration than in MeCN. This is also reflected by the effect on the shuttling: in the PrCN/PMAN system, a larger viscosity effect is observed compared to MeCN/PMAN. The shuttle is found to be slowed down in the polymer solutions but is still active at high viscosities. The observed retardation effect on the kinetics of shuttling in MeCN/PMAN and PrCN/PMAN can be correlated to the PMAN concentration through the hydrodynamic scaling model. The Stokes,Einstein relationship proves inadequate to correlate the shuttling rates to macroscopic viscosity, but the dependence of the shuttling rate on the bulk viscosity fits well to a commonly observed power-law relationship. The viscosity effect on the shuttling is found to be weak in all cases. [source] Synergistic Ordering of Side-Group Liquid Crystal Polymer and Small Molecule Liquid Crystal: Order and Phase Behavior of Nematic Polymer Solutions,MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 19-20 2007Neal R. Scruggs Abstract Addition of a small-molecule liquid crystal (5CB) to a cyanobiphenyl-based side-group liquid crystal polymer (SGLCP) stabilizes nematic order, increasing the isotropization temperature (TNI) more than 15,°C. Despite synergistic ordering at high concentration, small amounts of polymer destabilize nematic order. Even though TNI(SGLCP) is 27,°C greater than TNI(5CB), 2H NMR shows that the order parameter of the SGLCP is less than that of 5CB at concentrations for which monodomains were accessible (,10 wt.-%). The results imply that nematic order is frustrated in the bulk polymer and addition of small molecule LC relaxes this frustration by allowing greater configurational freedom. Conversely, adding small amounts of polymer to the bulk 5CB introduces frustration, resulting in the strong asymmetry of the phase diagram. [source] Thermodynamic Data of Polymer Solutions at Elevated PressuresMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 4 2006Bernhard Wolf No abstract is available for this article. [source] The Ludwig-Soret Effect on the Thermally Induced Phase Separation Process in Polymer Solutions: A Computational StudyMACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2009Sureshkumar B. Kukadiya Abstract The Ludwig-Soret effect was investigated in the thermally induced phase separation process via SD in polymer solutions under an externally imposed spatial linear temperature gradient using mathematical modeling and computer simulation. The mathematical model incorporated non-linear Cahn-Hilliard theory for SD, Flory-Huggins theory for thermodynamics, and the Ludwig-Soret effect for thermal diffusion. 2D simulation results revealed that the Ludwig-Soret effect had negligible impact on the phase separation mechanism in binary polymer solutions under a non-uniform temperature field, as reflected by the time evolution of the dimensionless structure factor and the transition time from the early to the intermediate stages of SD. [source] Accurate Prediction of , (Lower Critical Solution Temperature) in Polymer Solutions Based on 3D Descriptors and Artificial Neural NetworksMACROMOLECULAR THEORY AND SIMULATIONS, Issue 2-3 2008Jie Xu Abstract Quantitative structure-property relationships were studied between descriptors representing the three-dimensional structures of molecules and , (LCST, lower critical solution temperature) in polymer solutions with a database of 169 data containing 12 polymers and 67 solvents. Feed-forward artificial neural networks (ANNs) combined with stepwise multilinear regression analysis (MLRA) were used to develop the models. With ANNs, the squared correlation coefficient (R2) for , (LCST) of the training set of 112 systems is 0.9625, the standard error of estimation (SEE) is 13.43 K, and the mean relative error (MRE) is 1.99%; in prediction of , (LCST) using the test set of 57 systems, the MRE is 2.26%. With MLRA, the MREs for the training and test sets are 4.02% (R2,=,0.8739, SEE,=,25.88 K) and 5.05%, respectively. [source] Photoinduced Shuttling Dynamics of Rotaxanes in Viscous Polymer SolutionsADVANCED FUNCTIONAL MATERIALS, Issue 21 2009Dhiredj C. Jagesar Abstract The effect of external friction, caused by medium viscosity, on the photoinduced translational motion in a rotaxane-based molecular shuttle 1 is investigated. The shuttle is successfully operated in solutions of poly(methacrylonitrile) (PMAN) of different molecular weights in MeCN and PrCN. The viscosity of the medium is tuned by changing the PMAN concentration. The rheological behavior of the polymer solution gives insight into the structure of the polymer solution on the microscopic scale. In PrCN, the entanglement regime is reached at lower concentration than in MeCN. This is also reflected by the effect on the shuttling: in the PrCN/PMAN system, a larger viscosity effect is observed compared to MeCN/PMAN. The shuttle is found to be slowed down in the polymer solutions but is still active at high viscosities. The observed retardation effect on the kinetics of shuttling in MeCN/PMAN and PrCN/PMAN can be correlated to the PMAN concentration through the hydrodynamic scaling model. The Stokes,Einstein relationship proves inadequate to correlate the shuttling rates to macroscopic viscosity, but the dependence of the shuttling rate on the bulk viscosity fits well to a commonly observed power-law relationship. The viscosity effect on the shuttling is found to be weak in all cases. [source] Forming Highly Ordered Arrays of Functionalized Polymer Nanowires by Dewetting on Micropillars,ADVANCED MATERIALS, Issue 9 2007J. Guan 1D nanostructures are of great interest for numerous applications: a simple and low-cost process to generate large arrays of polymer nanowires by dewetting aqueous polymer solution on an array of micropillars is developed. These nanowires are typically less than 10,nm in lateral size and can be functionalized by incorporation of molecules or nanoparticles such as quantum dots (see figure). [source] Use of associating polymers as multifunctional thickeners: studies of Their structure in aqueous solutions via nmr, qels, fluorescence, And rheology measurementsINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 5 2007Katsunori Yoshida The solution properties of an associating polymer were studied by NMR, quasi-elastic light scattering (QELS), fluorescence, and rheology measurements. An associative thickening (AT) polymer was designed having a nonionic poly(ethylene oxide) backbone with long alkyl chains at both ends to achieve high viscosity even at relatively high salt concentrations and over a wide pH range. This study focuses on the associative state of the polymer in aqueous solutions at various polymer concentrations. In a fluorescence probe study using pyrene a spectral change in the I3/I1 ratio was observed for pyrene at a polymer concentration (Cp) of 3 x 10 -4%, indicating an apparent critical concentration (cmc) of the amphiphilic polymer. The viscosity, self-diffusion coefficient (Dsel), and hydrodynamic size (Rh) distribution measurements at various Cp all suggest that there is a second transition at Cp, 0.4%. Although we observed the discontinuity in viscosity, Dsel, and Rh at Cp, 0.4%, no changes in the relaxation times (T1 and T2) were recognized for either the alkyl chain or the ethylene oxide moiety of the polymer at C p= 0.1,1%. These data suggest that there are no structural changes or phase transitions at Cp, 0.4%, but that intermicellar networks are presumably formed by bridging of the end alkyl groups of the polymer, which is driven by hydrophobic forces. Because the polymer forms networks by hydrophobic interaction and the polymer itself is nonionic, the viscosity of the polymer solution was influenced very little by either the addition of salt or a pH change, as would be expected. The dynamic viscoelastic study revealed that the polymer solution exhibits a single mode Maxwell type relaxation behavior with a terminal relaxation time of about 0.61 s, which imparts a unique flow appearance to the polymer solutions. The time course measurements of the dynamic elastic modulus of the stratum corneum revealed that the polymer has excellent potential for skin softening. It was concluded that the associative thickening polymer not only is a useful thickener with a salt and pH tolerance but also has beneficial skincare effects. [source] Unique Phase-Separation Structures of Block-Copolymer Nanoparticles,ADVANCED MATERIALS, Issue 17 2005H. Yabu Block-copolymer nanoparticles with lamellar phase-separation structures (see Figure) have been prepared by a slow-precipitation process. Regular-sized polymer nanoparticles are formed after evaporation of a good solvent from a polymer solution containing a non-volatile poor solvent and a volatile good solvent. [source] The influence of electrospinning parameters on the structural morphology and diameter of electrospun nanofibersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Valencia Jacobs Abstract Electrospinning is a simple method of producing nanofibers by introducing electric field into the polymer solutions. We report an experimental investigation on the influence of processing parameters and solution properties on the structural morphology and average fiber diameter of electrospun poly ethylene oxide (PEO) polymer solution. Experimental trials have been conducted to investigate the effect of solution parameters, such as concentration, molecular weight, addition of polyelectrolyte in PEO solution, solvent effect, as well as governing parameter, such as applied voltage. The concentration of the aqueous PEO solution has shown noteworthy influence on the fiber diameter and structural morphology of electrospun nanofibers. At lower concentrations of PEO polymer solution, the fibers showed irregular morphology with large variations in fiber diameter, whereas at higher concentrations, the nanofibers with regular morphology and on average uniform fiber diameter were obtained. We find that the addition of polyelectrolytes, such as sodium salt of Poly acrylic acid (PAA) and Poly allylamine hydrochloride (PAH), increases the conductivity of PEO solutions and thereby decreases the bead formation in electrospun nanofibers. The increase in applied voltage has been found to affect the structural morphology of nanofiber while the addition of ethanol in PEO solution diminishes the bead defects. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Preparation of poly(ester imide) ultrafine fibers by gas-jet/electrospinningJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2009Bing Wang Abstract In this study, ultrafine fibers of poly(ester imide) (PEI) were produced by gas-jet/electrospinning of its solutions in mixtures of phenol and dichloromethane (DCM). The process parameters, including the solution concentration, gas flow rate, applied voltage, tip-to-collector distance (TCD), and inner diameter of the metal needle, were investigated by scanning electron microscopy. The results show that the solution concentration, gas flow rate, TCD, and inner diameter of the needle were the most important process parameters influencing the average diameter and morphology of the PEI gas-jet/electrospun fibers. An increase in the solution concentration resulted in a larger average diameter in the PEI gas-jet/electrospun fibers. Mixed-bead fibers were obtained when the concentration of PEI in phenol/DCM was below 20 wt % during gas-jet/electrospinning. A larger diameter of the capillary and a smaller gas flow rate favored the formation of ultrafine fibers with thicker fibers. Thinner and uniform PEI fibers with an average diameter of 298 nm were formed at a TCD of 25 cm. On the basis of the systematic parameters study, uniform PEI ultrafine fibers with an average diameter of 293 nm were prepared by this gas-jet/electrospinning with the following optimal process parameters: the concentration of the polymer solution was 20 wt %, the gas flow rate was 10.0 L/min, the applied voltage was 25.0 kV, the TCD was 25 cm, and the inner diameter of the metal needle was 0.24 mm. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Electrospinning of degradable elastomeric nanofibers with various morphology and their interaction with human fibroblastsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Erik Borg Abstract Artelon® (degradable poly(urethane urea) elastomer) was electrospun into scaffolds for tissue engineering. The diameter of the electrospun fibers, studied by scanning electron microscopy, ranged from 100 nm to a few ,m, with an average diameter of 750 nm. The molar mass of the polymer had a major influence on the morphology of the scaffold. Furthermore, aging of the polymer solution caused changes in viscosity, as measured by stress sweeps between 13.5,942 Pa that affected the morphology. The electrospun Artelon mats exhibited about the same elongations to break, both exceeding 200%, measured by tensile tests. The degradation study showed similar degradation behavior in electrospun mats and solids. In vitro study showed that human fibroblasts not only adhere to the surface but also migrate, proliferate, and produce components of an extracellular matrix. These results strongly support the use of electrospun Artelon as a scaffold in tissue engineering. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Stability of poly(N -propargylamide)s under ultraviolet irradiationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2008Jianping Deng Abstract This article investigates the photostability of poly(N -propargylamide)s under different conditions, on the basis of which application research for this class of highly functional polymers can be performed. With helical polymer 1 [monomer: CCCH2NHCOCH(C2H5)2] taken as a representative, some affecting factors, including the ultraviolet (UV)-light intensity, presence of oxygen, far-UV and near-UV light, and temperature, were investigated. It was found that increasing the UV-light intensity accelerated the degradation of polymer 1. When oxygen was present, it also facilitated the degradation. Far-UV light rather than near-UV light played a predominant role in initiating the degradation of polymer main chains. Elevating the temperature of the polymer solution during UV irradiation made the degradation accelerate. Storing the polymer under weak UV light, in the absence of oxygen, and at a low temperature was favorable for keeping the polymer stable. These findings are important not only from a scientific point of view but especially for developing practical applications of this type of polymer on the basis of its photodegradability. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Preparation of poly(ether sulfone) nanofibers by gas-jet/electrospinningJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008Yi Lin Abstract Poly(ether sulfone) (PES) nanofibers were prepared by the gas-jet/electrospinning of its solutions in N,N -dimethylformamide (DMF). The gas used in this gas-jet/electrospinning process was nitrogen. The morphology of the PES nanofibers was investigated with scanning electron microscopy. The process parameters studied in this work included the concentration of the polymer solution, the applied voltage, the tip,collector distance (TCD), the inner diameter of the needle, and the gas flow rate. It was found from experimental results that the average diameter of the electrospun PES fibers depended strongly on these process parameters. A decrease in the polymer concentration in the spinning solutions resulted in the formation of nanofibers with a smaller diameter. The use of an 18 wt % polymer solution yielded PES nanofibers with an average diameter of about 80 nm. However, a morphology of mixed bead fibers was formed when the concentration of PES in DMF was below 20 wt % during gas-jet/electrospinning. Uniform PES nanofibers with an average diameter of about 200 nm were prepared by this electrospinning with the following optimal process parameters: the concentration of PES in DMF was 25 wt %, the applied voltage was 28.8 kV, the gas flow was 10.0 L/min, the inner diameter of the needle was 0.24 mm, the TCD was 20 cm, and the flow rate was 6.0 mL/h. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source] Simulation of DNA electrophoresis in systems of large number of solvent particles by coarse-grained hybrid molecular dynamics approachJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2009Rong Wang Abstract Simulation of DNA electrophoresis facilitates the design of DNA separation devices. Various methods have been explored for simulating DNA electrophoresis and other processes using implicit and explicit solvent models. Explicit solvent models are highly desired but their applications may be limited by high computing cost in simulating large number of solvent particles. In this work, a coarse-grained hybrid molecular dynamics (CGH-MD) approach was introduced for simulating DNA electrophoresis in explicit solvent of large number of solvent particles. CGH-MD was tested in the simulation of a polymer solution and computation of nonuniform charge distribution in a cylindrical nanotube, which shows good agreement with observations and those of more rigorous computational methods at a significantly lower computing cost than other explicit-solvent methods. CGH-MD was further applied to the simulation of DNA electrophoresis in a polymer solution and in a well-studied nanofluidic device. Simulation results are consistent with observations and reported simulation results, suggesting that CGH-MD is potentially useful for studying electrophoresis of macromolecules and assemblies in nanofluidic, microfluidic, and microstructure array systems that involve extremely large number of solvent particles, nonuniformly distributed electrostatic interactions, bound and sequestered water molecules. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009 [source] Modeling the mass transfers during the elaboration of chitosan-activated carbon composites for medical applicationsAICHE JOURNAL, Issue 6 2010A. Venault Abstract Hydrogels composites composed of chitosan and activated carbon were prepared for medical applications using the vapor-induced phase separation process. Since the gelation process involves mass exchanges between the polymer solution and the air, the kinetics of mass transfer were investigated through experimental and modeling approaches. Among the formulation and process parameters, gravimetric measurements exhibited that mass transfers were mostly controlled by the initial ammonia partial pressure. A nonisotherm mass-transfer model was developed to predict the nonsolvent and solvent exchange rates, therefore, the water and ammonia concentration profiles within the sample during the process. The numerical results were successively validated with gravimetrical kinetic curves obtained in a chamber where the process parameters were controlled. The model aimed also at predicting the pH moving front along the film thickness. The gelation time could also be predicted for different operating conditions (formulation and process parameters). © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Estimation of an effective water diffusion coefficient during infrared-convective drying of a polymer solutionAICHE JOURNAL, Issue 9 2009N. Allanic Abstract This article deals with the drying of an aqueous solution of polyvinyl alcohol mixed with a plasticizer. A heating combining forced convection and short-infrared radiation was investigated. A one-dimensional model taking into account the shrinkage of the product was developed to get the temperature and moisture content evolutions during the drying. The water diffusion coefficient was estimated by an inverse method. A sensitivity analysis and numerical tests showed the relevance of using an objective function taking both mass and temperature measurements into account for the estimation procedure. This estimation was performed on several convective and infrared-convective experimental drying kinetics. The model predictions fit well mass and temperature experimental data. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] The influence of solution-state conditions and stirring rate on the assembly of poly(acrylic acid)-containing amphiphilic triblock copolymers with multi-aminesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2010Jennifer L. Sorrells Abstract In the effort towards making nanoscale objects and assemblies feasible for use as functional materials, it is imperative to obtain control over the fundamental architectures and essential to understand what experimental conditions cause the manifestation of specific morphologies. A number of factors are known to influence the shape during the self-assembly of amphiphilic block copolymers in solution, including solvent composition, polymer length, hydrophobicity versus hydrophilicity, as well as the addition of additives that can interact with segments of the block copolymers. This research, focused on developing an understanding of the micellar architectures accessed by the amphiphilic triblock copolymer of acrylic acid, methyl acrylate, and styrene, PAA85 - b -PMA40 - b -PS35, as a function of the stirring rate, together with other factors, when undergoing coassembly with ethylenediamine or diethylenetriamine in water/tetrahydrofuran solutions. The work demonstrates that the rate at which the polymer solution was stirred impacts the shape of the solution-state assemblies formed by the triblock copolymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 [source] Preparation of novel acrylamide-based thermoresponsive polymer analogues and their application as thermoresponsive chromatographic matricesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2008Yoshikatsu Akiyama Abstract New thermoresponsive polymers based on poly(N -(N, -alkylcarbamido)propyl methacrylamide) analogues were designed with increased hydrophobic content to facilitate temperature-dependent chromatographic separations of peptides and proteins from aqueous mobile phases. These polymer solution exhibited a lower critical solution temperature (LCST) when the alkyl group is methyl, ethyl, isopropyl, propyl, butyl, and isobutyl. However, larger alkyl groups such as hexyl and phenyl were not soluble in aqueous solutions at any temperature. Phase transition temperatures were lower for larger alkyl groups and increased with decreasing polymer molecular weight and concentration in solution. LCST dependence on polymer molecular weight and concentration is more significant compared with well-studied poly(N -isopropylacrylamide) (PIPAAm). Partition coefficient (log P) values for N -(N, -butylcarbamide)propylmethacrylamide and N -(N, -isobutylcarbamide)propyl methacrylamide (iBuCPMA) monomers are larger than that for IPAAm monomer, suggesting higher hydrophobicity than IPAAm. Chromatographic evaluation of poly(N -(N, -isobutylcarbamide)propyl methacrylamide) (PiBuCPMA) grafted silica particles in aqueous separations revealed larger k, values for peptides, insulin, insulin chain B, and angiotensin I than PIPAAm-grafted silica beads. In particular, k, values for insulin obtained from PiBuCPMA-grafted silica separations were much larger than those from PIPAAm-grafted surface separations, indicating that PiBuCPMA should be more hydrophobic than PIPAAm. These results support the introduction of alkylcarbamido groups to efficiently increase thermoresponsive polymer hydrophobicity of poly(N -alkylacrylamides) and poly(N -alkylmethacrylamides). Consequently, poly(N -(N, -alkylcarbamido)propyl methacrylamide) analogues such as PiBuCPMA and poly(N -(N, -alkylcarbamido)alkylmehacrylamide) are new thermoresponsive polymers with appropriate hydrophobic partitioning properties for protein and peptide separations in aqueous media, depending on selection of their alkyl groups. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5471,5482, 2008 [source] Solvent-induced self-organization approach for polymeric architectures of micropores, hexagons and spheres based on polyurethanes prepared via novel melt transurethane methodologyJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2007P. Deepa Abstract Solvent-induced self-organization approach was developed, for the first time, to produce polyurethane microporous templates and higher ordered morphologies such as micro or nanometer-sized polymeric hexagons and spheres. A novel melt transurethane methodology was designed and developed for synthesizing new class of cycloaliphatic polyurethanes under nonisocyanate and solvent-free conditions. In this new process, a diurethane monomer was polycondensed with equimolar amounts of diol in presence of Ti(OBu)4 as catalyst with the removal of low boiling alcohol from the equilibrium. The hydrogen bonding of the polyurethanes are very unique to their chemical structure and they undergo selective phase-separation process in solution to produce hexagonally packed microporous templates. The increase of water content in the polymer solution enhances the phase-separation process and the micro pores coalesce to isolate the encapsulated polymer matrix into polymeric hexagons or densely packed solid spheres. The concentration-dependent solution FTIR and 1H NMR of the polyurethanes revealed that the polymers possessing higher H-bonding association constants (K) have greater tendency to undergo solvent-induced self-organization phenomena. The mechanism of solvent-evaporation process indicated that only microporous polyurethanes have tendency to form higher ordered hexagons and spheres whereas others failed to show any new morphology. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2351,2366, 2007 [source] Acrylic Triblock Copolymer Design for Thermoreversible Gelcasting of Ceramics: Rheological and Green Body PropertiesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2009M. E. Seitz Thermoreversible gelcasting (TRG) is an attractive net-shape powder-based processing technique which relies on the temperature-driven gelation of a polymer solution. This study uses the TRG of alumina to investigate the implications of triblock copolymer design (block length, endblock fraction, and midblock chemistry) on rheological and green body properties. The liquid-to-solid transition and relaxation time in the gel state are controlled by the polymer's endblock length while the total polymer length controls the viscosity at high temperature. Although triblock design and concentration do not affect the green body porosity or sintered density, they do have significant effects on green body behavior. Triblocks with a high fraction of rubbery midblock behave as elastomers and confer significant toughness to the green bodies. In contrast, those with glassy midblocks increase the strength of the body but also behave in a brittle manner. Green body strength increases with increasing triblock concentration and is well described by a model for the strength of ceramic bodies with the binder localized at the particle necks. [source] A composite material model for improved bone formationJOURNAL OF TISSUE ENGINEERING AND REGENERATIVE MEDICINE, Issue 7 2010Silvia Scaglione Abstract The combination of synthetic polymers and calcium phosphates represent an improvement in the development of scaffolds for bone-tissue regeneration. Ideally, these composites provide both mechanically and architecturally enhanced performances; however, they often lack properties such as osteoconductivity and cell bioactivation. In this study we attempted to generate a composite bone substitute maximizing the available osteoconductive surface for cell adhesion and activity. Highly porous scaffolds were prepared through a particulate leaching method, combining poly-,-caprolactone (PCL) and hydroxyapatite (HA) particles, previously coated with a sucrose layer, to minimize their embedding by the polymer solution. Composite performances were evaluated both in vitro and in vivo. In PCL,sucrose-coated HA samples, the HA particles were almost completely exposed and physically distinct from the polymer mesh, while uncoated control samples showed ceramic granules massively covered by the polymer. In vivo results revealed a significant extent of bone deposition around all sucrose-coated HA granules, while only parts of the control uncoated HA granules were surrounded by bone matrix. These findings highlight the possibility of generating enhanced osteoconductive materials, basing the scaffold design on physiological and cellular concepts. Copyright © 2010 John Wiley & Sons, Ltd. [source] Application of Nitroxide-Terminated Polymers Prepared by Sonochemical Degradation in the Synthesis of Block CopolymersMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 2 2006Martina Bartsch Abstract Summary: The ultrasonic irradiation of a polymer solution results in the breakage of macromolecular CC bonds. In the presence of radical scavengers the formed macroradicals are prevented from termination reactions as combination or disproportionation. Using nitroxides as trapping agents the polymer is transformed into a macroinitiator, which can be used in controlled free-radical polymerization to synthesize block copolymers. In this work several polymers were exposed to sonochemical degradation and terminated with various nitroxides, e.g. OH-TEMPO and TIPNO. In a second reaction step the prepared polymer-nitroxide-adducts were applied as macroinitiators in controlled free-radical polymerizations with styrene. The obtained products were mixtures of block copolymer and the corresponding homopolymers. The visco-elastic properties were investigated by rheological analysis. A special separation technique with selective solvents was applied to determine the content of block copolymer. Synthesis of block copolymers with sonochemically prepared macroinitiators. [source] A Novel Route for Fabricating Metal-Polymer Composite Nanoparticles with Phase-Separated StructuresMACROMOLECULAR RAPID COMMUNICATIONS, Issue 14 2010Hiroshi Yabu Abstract Au nanoparticles (NPs) and polymer composite particles with phase-separation structures were prepared based on phase separation structures. Au NPs were successfully synthesized in amphiphilic block-copolymer micelles, and then composite particles were formed by a simple solvent evaporation process from Au NPs and polymer solution. The phase separated structures (Janus and Core-shell) were controlled by changing the combination of polymers having differing hydrophobicity. [source] Effect of Concentration Gradient on the Morphology Development in Polymer Solutions Undergoing Thermally Induced Phase SeparationMACROMOLECULAR THEORY AND SIMULATIONS, Issue 7 2007Bai Tao Jiang Abstract Anisotropic porous polymeric materials fabricated from the phase separation method via spinodal decomposition are used in various practical engineering applications. We studied the formation of anisotropic porous polymeric materials numerically, by imposing an initial linear concentration gradient across a model polymer solution. The initial concentration gradient is placed at three different regions of the polymer sample for comparison purposes. All the simulation results are in good agreement with published experimental observations, which are reported from the applications of porous polymeric membranes. The structure development shows that an anisotropic porous morphology forms when an initial linear concentration gradient is applied to the model polymer solution. [source] White light generation through yellow nanophosphor and blue organic light-emitting diodePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2009Je Hong Park Abstract White light-emitting device (WLED) combining yellow-emitting nanophosphor and blue organic light-emitting diode (LED) was developed. WLED was fabricated by using a spin-coating method. Yellow-emitting nanophosphor was dispersed in the blue-emitting polymer solution for spin-coating. As a variation of mixture ratio of yellow-emitting nanophosphor and blue-emitting polymer in emitting layer, the emission spectra were studied. Our white organic light-emitting device with 30% phosphor mixture ratio and at the driving voltage of 17 V showed the color coordinates of x = 0.266 and y = 0.33. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electrospinning functional nanoscale fibers: a perspective for the futurePOLYMER INTERNATIONAL, Issue 3 2008Matthew T Hunley Abstract Over the past decade, electrospinning has grown from a small niche process to a widely used fiber formation technique. Applying a strong electric potential on a polymer solution or melt produces nanoscale fibers. These nanofibers form non-woven textile mats, oriented fibrous bundles and even three-dimensional structured scaffolds, all with large surface areas and high porosity. Major applications of electrospun membranes include tissue engineering, controlled drug delivery, sensing, separations, filtration, catalysis and nanowires. This perspective article highlights many recent advances in electrospun fibers for functional applications, with an emphasis on the advantages and proposed technologies for these non-woven fibrous scaffolds. Copyright © 2007 Society of Chemical Industry [source] Mobility control: How injected surfactants and biostimulants may be forced into low-permeability unitsREMEDIATION, Issue 3 2003Richard E. Jackson Recovering dense nonaqueous-phase liquid (DNAPL) remains one of the most difficult problems facing the remediation industry. Still, the most common method of recovering DNAPL is to physically remove the contaminants using common technologies such as total fluids recovery pumps, vacuum systems, and "pump-and-treat." Increased DNAPL removal can be attained using surfactants to mobilize and/or solubilize the pollutants. However, very little is understood of the methods developed by petroleum engineers beginning in the 1960s to overcome by-passed, low-permeability zones in heterogeneous oil reservoirs. By injecting or causing the formation of viscous fluids in the subsurface, petroleum engineers caused increased in-situ pressures that forced fluid flow into low permeability units as well as the higher permeability thief zones. Polymer flooding involves injecting a viscous aqueous polymer solution into the contaminated aquifer. Foam flooding involves injecting surfactant to decontaminate the high-permeability zones and then periodic pulses of air to cause a temporary viscous foam to form in the high-permeable zones after all DNAPL is removed. Later surfactant pulses are directed by the foam into unswept low-permeable units. These methods have been applied to DNAPL removal using surfactants but they can also be applied to the injection of bio-amendments into low-permeability zones still requiring continued remediation. Here we discuss the principles of mobility control as practiced in an alluvial aquifer contaminated with chlorinated solvent and coal tar DNAPLs as well as some field results. © 2003 Wiley Periodicals, Inc. [source] Experimental research on drag reduction by polymer additives in a turbulent pipe flowTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2002Shao Xueming Abstract In order to investigate the effects of injection position on drag reduction as well as further the effects of polymer additives on turbulent structures, LDA measurements of turbulent pipe flows were conducted. The results show that the amount of drag reduction grows with the increase of the Reynolds number, and injecting the polymer at the centre of pipe is more effective than at the wall. Due to the addition of polymer solution, the axial, radial r.m.s. velocity fluctuations and Reynolds stress decrease over the entire pipe cross-section, the time auto-correlation coefficients of axial and radial velocity fluctuation at the centre of pipe decay more slowly, the number of spectrum peaks is decreased, and the peak shifts towards lower wave numbers. The results also reveal that, due to the addition of polymer solution, the large-scale vortices are enhanced and small-scale vortices are suppressed. On a effectué des mesures par anémométrie laser Doppler d'écoulements turbulents dans des conduites afin d'étudier l'effet de la position de l'injection et l'effet de l'ajout d'additifs à base de polymères sur la réduction de traînée. Les résultats montrent que la réduction de traînée augmente avec le nombre de Reynolds et qu'il est plus efficace d'injecter le polymère au centre de la conduite qu'à la paroi. Du fait de l'ajout d'une solution de polymères, les fluctuations de vitesse efficace radiale et axiale et la contrainte de Reynolds diminuent sur toute la section transversale de la conduite, les coefficients d'auto-corrélation de temps de la fluctuation de vitesse efficace radiale et axiale au centre de la conduite décroissent plus lentement, le nombre de pics du spectre diminue et les pics tendent à avoir un nombre d'ondes moins grand. Les résultats montrent également que, grâce à l'ajout de la solution de polymères, les tourbillons de grande échelle sont plus nombreux tandis que les tourbillons de petite eéhelle disparaissent. [source] Experimental Study on the Molecular Dimension and Configuration of Polymer and Its Flow Characteristics from Electrolyte EffectCHINESE JOURNAL OF CHEMISTRY, Issue 4 2009Xiangguo LU Abstract Molecular clew dimension and configuration of polymer, and flow characteristics of polymer solution were studied from electrolyte effect, by making use of dynamic light scattering (DLS), scanning electron microscopy (SEM), apparent viscosity method and core flow experiment. It can be observed that with the electrolyte concentration increasing, there exists a variation trend of "decreasing, increasing and decreasing again" to the molecular clew dimension of the polymer. The compression action of Ca2+ or Mg2+ to the double electrode layer of polymer molecules is more powerful by comparison against Na+, which results in that Ca2+ and Mg2+ have a more extensive effect on the viscosity of polymer solution, and clew dimensions and their distribution. With the electrolyte concentration increasing, the polymer molecular configuration of multi-layer stereoscopic random reticulation transformed into a dendritic one. During the succeeding water flooding, the variation degree of injection pressure of core was mainly determined by the swelling extent of molecular clew of retained polymer and the produced amount of polymer. And the bigger the molecular weight of polymer is, the stronger the compression or swelling action of electrolyte to the molecule clews is, and the greater the increasing degree of injection pressure during succeeding water flooding is. The greater difference of electrolyte concentrations in used water between polymer flooding and succeeding water flooding can result in greater increasing degree of injection pressure during the succeeding water flooding. So, an advisable increasing in difference of electrolyte concentrations in used water between the polymer flooding and succeeding water flooding was proposed when designing the polymer flooding performance in oilfields, which has promising result for improving effect of polymer flooding. [source] | ||||||||||||||||||||||||||||||||||