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Interaction Parameter (interaction + parameter)
Selected AbstractsEffect of Chain-Length Dependence of Interaction Parameter on Spinodals for Polydisperse Polymer BlendsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 5 2006Xiyan Du Abstract Summary: The chain-length dependence of the Flory-Huggins (FH) interaction parameter is introduced into the FH lattice theory for polydisperse polymer-blend systems. The spinodals are calculated for the model polymer blends with different chain lengths and distributions. It is found that all the related variables, rn, rw, rz, and chain-length distribution, have effects on the spinodals for polydisperse polymer blends. The spinodals at different chain lengths. [source] Synthesis of Poly(4-vinylpyridine) Thin Films by Initiated Chemical Vapor Deposition (iCVD) for Selective Nanotrench-Based Sensing of NitroaromaticsADVANCED FUNCTIONAL MATERIALS, Issue 7 2010Wyatt E. Tenhaeff Abstract A new nanoscale sensing concept for the detection of nitroaromatic explosives is described. The design consists of nitroaromatic-selective polymeric layers deposited inside microfabricated trenches. As the layers are exposed to nitroaromatic vapors, they swell and contact each other to close an electrical circuit. The nitroaromatic selective polymer, poly(4-vinylpyridine) (P4VP), is deposited in the trenches using initiated chemical vapor deposition (iCVD). P4VP is characterized for the first time as a selective layer for the absorption of nitroaromatic vapors. The Flory,Huggins equation is used to model the swelling response to nitroaromatic vapors. The Flory,Huggins interaction parameter for the P4VP,nitrobenzene system at 40,°C is 0.71 and 0.25 for P4VP,4-nitrotoluene at 60,°C. Sensing of nitrobenzene vapors is demonstrated in a prototype device, while techniques to improve the performance of the design in terms of response time and sensitivities are described. Modeling shows that concentration and mass limits of detection of 0.95,ppb and 3 fg, respectively, can be achieved. [source] Effect of magnetic Reynolds number on the two-dimensional hydromagnetic flow around a cylinderINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2009T. V. S. Sekhar Abstract Numerical experiments have been conducted to study the effect of magnetic Reynolds number on the steady, two-dimensional, viscous, incompressible and electrically conducting flow around a circular cylinder. Besides usual Reynolds number Re, the flow is governed by the magnetic Reynolds number Rm and Alfvén number ,. The flow and magnetic field are uniform and parallel at large distances from the cylinder. The pressure Poisson equation is solved to find the pressure fields in the entire flow region. The effects of the magnetic field and electrical conductivity on the recirculation bubble, drag coefficient, standing vortex and pressure are presented and discussed. For low interaction parameter (N<1), the suppression of the flow-separation is nearly independent of the conductivity of the fluid, whereas for large interaction parameters, the conductivity of the fluid strongly influences the control of flow-separation. Copyright © 2008 John Wiley & Sons, Ltd. [source] Competitive plasticization in ternary plasticized starch biopolymer systemJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010Deeptangshu S. Chaudhary Abstract Two plasticizers namely, glycerol and xylitol, based on their similar molecular diameter (, 6.3 Å) but different molecular weights (glycerol-92; xylitol-152) were selected were selected for studying the plasticization of starch biopolymer containing 70% amylopectin structure via glass transition measurements carried over a wide range of water activity. A standard calorimetry was used to determine the onset temperature of polymeric viscous flow. For both glycerol and xylitol, typical antiplasticization was evident at low plasticizer concentrations, whereas at higher concentration, there was significant reduction in glass transition temperature. Water activity isotherms showed that equilibrium moisture content of the starch biopolymer (no plasticizer) steadily increases up to 11%, however, for plasticized biopolymer, the moisture content was nearly double than that of biopolymer. We used a modified Gordon-Taylor model, using a new interaction parameter, to understand the competitive plasticization of glycerol and xylitol in presence of water, and determined 8 wt % water as a threshold amount of matrix water for strong three-way interactions: starch-plasticizer, plasticizer-plasticizer/water and starch-water. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Description of the mutual solubilities of fatty acids and water with the CPA EoSAICHE JOURNAL, Issue 6 2009M. B. Oliveira Abstract Data for the mutual solubilities of fatty acid + water mixtures are scarce and so measurements for seven fatty acid (C5 -C10, C12) + water systems were carried out. This new experimental data was successfully modelled with the cubic plus association EoS. Using data from C6 to C10 and the Elliot's cross-associating combining rule a correlation for the kij binary interaction parameter, as a function of the acid chain length, is proposed. The mutual solubilities of water and fatty acids can be adequately described with average deviations inferior to 6% for the water rich phase and 30% for the acid rich phase. Furthermore, satisfactory predictions of solid-liquid equilibria of seven fatty acids (C12 -C18) + water systems were achieved based only on the kij correlation obtained from liquid,liquid equilibria data. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] A new formulation of garnet,clinopyroxene geothermometer based on accumulation and statistical analysis of a large experimental data setJOURNAL OF METAMORPHIC GEOLOGY, Issue 7 2009D. NAKAMURAArticle first published online: 13 JUL 200 Abstract Published experimental data including garnet and clinopyroxene as run products were used to develop a new formulation of the garnet,clinopyroxene geothermometer based on 333 garnet,clinopyroxene pairs. Only experiments with graphite capsules were selected because of difficulty in estimating the Fe3+ content of clinopyroxene. For the calibration, a published subregular-solution model was adopted to express the non-ideality of garnet. The magnitude of the Fe,Mg excess interaction parameter for clinopyroxene (WFeMgCpx), and differences in enthalpy and entropy of the Fe,Mg exchange reaction were regressed from the accumulated experimental data set. As a result, a markedly negative value was obtained for the Fe,Mg excess interaction parameter of clinopyroxene (WFeMgCpx = , 3843 J mol,1). The pressure correction is simply treated as linear, and the difference in volume of the Fe,Mg exchange reaction was calculated from a published thermodynamic data set and fixed to be ,120.72 (J kbar,1 mol,1). The regressed and obtained thermometer formulation is as follows: where T = temperature, P = pressure (kbar), A = 0.5 Xgrs (Xprp , Xalm , Xsps), B = 0.5 Xgrs (Xprp , Xalm + Xsps), C = 0.5 (Xgrs + Xsps) (Xprp , Xalm), Xprp = Mg/(Fe2+ + Mn + Mg + Ca)Grt, Xalm = Fe/(Fe2+ + Mn + Mg + Ca)Grt, Xsps = Mn/(Fe2+ + Mn + Mg + Ca)Grt, Xgrs = Ca/(Fe2+ + Mn + Mg + Ca)Grt, XMgCpx = Mg/(Al + Fetotal + Mg)Cpx, XFeCpx = Fe2+/(Al + Fetotal + Mg)Cpx, KD = (Fe2+/Mg)Grt/(Fe2+/Mg)Cpx, Grt = garnet, Cpx = clinopyroxene. A test of this new formulation to the accumulated data gave results that are concordant with the experimental temperatures over the whole range of the experimental temperatures (800,1820 °C), with a standard deviation (1 sigma) of 74 °C. Previous formulations of the thermometer are inconsistent with the accumulated data set; they underestimate temperatures by about 100 °C at >1300 °C and overestimate by 100,200 °C at <1300 °C. In addition, they tend to overestimate temperatures for high-Ca garnet (Xgrs , 0.30,0.50). This new formulation has been tested against previous formulations of the thermometer by application to natural eclogites. This gave temperatures some 20,100 °C lower than previous formulations. [source] Determination of cubic equation of state parameters for pure fluids from first principle solvation calculationsAICHE JOURNAL, Issue 8 2008Chieh-Ming Hsieh Abstract A new method for estimation of parameters in cubic equations of state from ab initio solvation calculations is presented. In this method, the temperature-dependent interaction parameter a(T) is determined from the attractive component of solvation free energy, whereas the volume parameter b is assumed to be that of solvation cavity. This method requires only element-specific parameters, i.e., atomic radius and dispersion coefficient, and nine universal parameters for electrostatic and hydrogen-bonding interactions. The equations of state (EOS) parameters so determined allow the description of the complete fluid phase diagram, including the critical point. We have examined this method using the Peng,Robinson EOS for 392 compounds and achieved an accuracy of 43% in vapor pressure, 17% in liquid density, 5.4% in critical temperature, 11% in critical pressure, and 4% in critical volume. This method is, in principle, applicable to any chemical species and is especially useful for those whose experimental data are not available. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source] Chemisorption of carbon dioxide on sodium oxide promoted aluminaAICHE JOURNAL, Issue 11 2007K. B. Lee Abstract New equilibrium and column dynamic data for chemisorption of carbon dioxide from inert nitrogen at 250, 350, and 450°C were measured on a sample of sodium oxide promoted alumina, which was found to be a reversible chemisorbent for CO2. The equilibrium chemisorption isotherms were Langmuirian in the low pressure region (p <2.0 kPa) with a large gas,solid interaction parameter. The isotherms deviated from the Langmuirian behavior in the higher pressure region. A new analytical model which simultaneously accounted for Langmuirian chemisorption of CO2 on the adsorbent surface and additional reaction between the gaseous and sorbed CO2 molecules was used to describe the measured equilibrium data. The heats of CO2 chemisorption and the additional surface reaction were, respectively, 64.9 and 37.5 kJ/mol. The column breakthrough curves for CO2 sorption from inert N2 on the chemisorbent as well as the desorption of CO2 from the chemisorbent by N2 purge at 350°C could be described by the linear driving force (LDF) model in conjunction with the new sorption isotherm. The same LDF mass transfer coefficients can be used to describe both sorption and desorption processes. The CO2 mass transfer coefficients were (i) independent of feed gas CO2 concentration in the range of the data at a given temperature, and (ii) a weak function of temperature. The ratio of the mass transfer zone length to the column length was very small due to highly favorable CO2 sorption equilibrium. Several sequential cyclic CO2 sorption,desorption column dynamic tests were conducted to demonstrate the apparent stability of the material. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Phase equilibrium in supercritical CO2 mixtures using a modified Kwak-Mansoori mixing ruleAICHE JOURNAL, Issue 2 2004José O. Valderrama Abstract The mixing rules proposed by Kwak and Mansoori for the Peng-Robinson equation of state have been modified to describe vapor-liquid equilibrium in mixtures that contain supercritical CO2. Data in the literature for nine binary liquid,vapor systems containing supercritical CO2 are used for testing the modified models. The systems studied were binary mixtures containing carbon dioxide with lauric acid, palmitic acid, oleic acid, linoleic acid, 1-octanol, 1-decanol, 2-methyl-1-pentanol, ,-pinene, and limonene. The modifications studied included the introduction of a nonquadratic mixing rule proposed by one of the authors and a different interaction parameter for the volume constant of the equation of state. Compared to results in the literature, the Kwak-Mansoori combining rules and the proposed empirical modifications give lower deviations in correlating the solute concentration in the vapor phase, the most important variable for the design of supercritical extraction processes. Contrary to arguments found in the literature, it is also demonstrated that a severe test for an equation of state and its mixing rules is the correlation of the solute concentration in vapor,liquid mixtures. © 2004 American Institute of Chemical Engineers AIChE J, 50: 480,488, 2004 [source] Solubilization of hydrophobic drugs by methoxy poly(ethylene glycol)-block-polycaprolactone diblock copolymer micelles: Theoretical and experimental data and correlationsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2008Kevin Letchford Abstract The solubilization of five model hydrophobic drugs by a series of micelle-forming, water-soluble methoxy poly(ethylene glycol)-block-polycaprolactone diblock copolymers (MePEG-b-PCL) with varying methoxy poly(ethylene glycol) (MePEG) and polycaprolactone (PCL) block lengths was investigated. Variation of the feed weight ratio of MePEG to caprolactone resulted in the synthesis of copolymers with predictable block lengths. The micelle diameter and pyrene partition coefficient (Kv) were directly related to the PCL block length whereas the critical micelle concentrations (CMC) were inversely related to the PCL block length. The aqueous solubilities of the model hydrophobic drugs, indomethacin, curcumin, plumbagin, paclitaxel, and etoposide were increased by encapsulation within the micelles. Drug solubilization was directly related to the compatibility between the solubilizate and PCL as determined by the Flory,Huggins interaction parameter (,sp). Furthermore, the concentration of solubilized drug was also directly related to the PCL block length. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:1179,1190, 2008 [source] Kinetics of the volume phase transition in poly(n -isopropylacrylamide) gels prepared under high pressureJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2001Tadayosi Kitada Abstract New poly(N -isopropylacrylamide) gels were prepared under high pressure (ca. 200 MPa) during gelation. The preparation-pressure dependence of the deswelling speed of the gels was measured with a conventional T-jump method. The deswelling time of a gel rod 2.2 mm in diameter prepared at 193 MPa was about 200 s, 1000 times faster than that of a homogeneous poly(N -isopropylacrylamide) gel. Moreover, the collective diffusion coefficient, the thermal fluctuation, and the ensemble-average intensity of the swollen gel networks were obtained with dynamic light scattering measurements. Both the enthalpy and entropy of the gels were estimated from equilibrium swelling curves with the Flory,Huggins interaction parameter evaluated with mean field theory based on the Flory-type of the Gibbs free-energy formula. It was found that the networks of the gels had an inhomogeneous structure newly introduced by the preparation pressure. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2315,2325, 2001 [source] Spousal Concordance for Alcohol Dependence: Evidence for Assortative Mating or Spousal Interaction Effects?ALCOHOLISM, Issue 5 2007Julia D. Grant Background: Alcohol dependence (AD) is among the most common psychiatric disorders, and impacts the health and well-being of problem drinkers, their family members, and society as a whole. Although previous research has consistently indicated that genetic factors contribute to variance in risk for AD, little attention has been paid to nonrandom mating for AD. When assortative mating occurs for a heritable trait, spouses are genetically correlated and offspring are at increased risk of receiving high-risk genes from both parents. The primary goal of the present analyses is to test hypotheses about the source(s) and magnitude of spousal associations for AD using a twin-spouse design. Methods: DSM-IV AD (without the clustering criterion) was assessed via telephone interview for 5,974 twin members of an older cohort of the Australian Twin Register (born 1902,1964) and 3,814 spouses of the twins. Quantitative genetic modeling was used to determine the extent to which variability in risk for AD was influenced by genetic factors, the extent of spousal association for AD, and whether the association was attributable to assortative mating, reciprocal spousal interaction, or both processes. Results: Genetic factors explained 49% of the variance in risk for AD. There was no evidence of gender differences in the spousal interaction effect, the degree of rater bias, or the association between the twin's report of spouse AD and the spouse's AD phenotype. Either the assortative mating parameter or the spousal interaction parameter could be removed from the model without a significant decrement in fit, but both could not be dropped simultaneously, suggesting a lack of power to differentiate between these 2 causes of spousal correlation. When both effects were included in the model, the spousal correlation was 0.29, the assortative mating coefficient was 0.45 (i.e., "like marries like"), and the reciprocal spousal interaction coefficient was ,0.10 (i.e., after controlling for assortative mating, the additional impact of spousal interactions is slightly protective). Conclusions: These analyses provide evidence of significant spousal associations for AD, with assortative mating increasing spouse similarity and spousal interaction effects decreasing it after controlling for assortative mating. Although the genetic impact is modest, assortative mating results in an increased proportion of offspring exposed to 2 alcoholic parents and the associated detrimental environmental sequelae, and increases the likelihood of offspring inheriting high-risk genes from both parents. [source] Adsorption interaction parameter of polyethers in ternary mobile phases: The critical adsorption lineJOURNAL OF SEPARATION SCIENCE, JSS, Issue 8 2010Nguyen V. Cuong Abstract It is shown that in LC of polymers, the interaction parameter in ternary mobile phases can be described by a plane, which is determined by the dependencies in binary mobile phases. Instead of a critical adsorption point, critical conditions are observed along a straight line of composition between the two critical points in binary mobile phases. Consequently, a separation of block copolymers under critical conditions for one block by an adsorption mechanism for the other block can be achieved in ternary mobile phases of different compositions, which allows an adjustment of the retention of the adsorbing block. [source] Isothermal Crystallization Kinetics of Poly(, -caprolactone) with Tetramethyl Polycarbonate and Poly(styrene- co -acrylonitrile) Blends Using Broadband Dielectric SpectroscopyMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 11 2006Samy A. Madbouly Abstract Summary: Phase behavior and isothermal crystallization kinetics of poly(, -caprolactone) (PCL) blends with tetramethyl polycarbonate (TMPC) and poly(styrene- co -acrylonitrile) with 27.5 wt.-% acrylonitrile content have been investigated using broadband dielectric spectroscopy and differential scanning calorimeter. An LCST-type phase diagram has been observed for PCL/SAN blend while all the different blend compositions of PCL/TMPC were optically clear without any phase separation structure even at high temperatures up to 300,°C. The composition dependence of Tgs for both blends has been well described by the Gordon-Taylor equation. The phase diagram of PCL/SAN was theoretically calculated using the Flory-Huggins equation considering that the interaction parameter is temperature and composition dependent. The equilibrium melting point of PCL depressed in the blend and the magnitude of the depression was found to be composition dependent. The interaction parameters of PCL with TMPC and SAN could not be calculated from the melting point depression based on Nishi-Wang approach. The isothermal crystallization kinetics of PCL and in different blends was also investigated as a function of crystallization temperature using broadband dielectric spectroscopy. For pure PCL the rate of crystallization was found to be crystallization temperature (Tc) dependent, i.e., the higher the Tc, the lower the crystallization rate. The crystallization kinetics of PCL/TMPC blend was much slower than that of PCL/SAN at a constant crystallization temperature. This behavior was attributed to the fact that PCL is highly interacted with TMPC than SAN and consequently the stronger the interaction the higher the depression in the crystallization kinetics. It was also attributed to the different values of Tg of TMPC (191,°C) and SAN (100,°C); therefore, the tendency for crystallization decreases upon increasing the Tg of the amorphous component in the blend. The analysis of the isothermal crystallization kinetics was carried out using the theoretical approach of Avrami. The value of Avrami exponent was almost constant in the pure state and in the blends indicating that blending simply retarded the crystallization rate without affecting the crystallization mechanism. Dielectric constant, ,,, of pure PCL, blends of PCL/TMPC,=,80/20 and PCL/SAN,=,80/20 as a function of crystallization time at 47,°C and 1 kHz. [source] Thermodynamics of Phase Behavior in PEO/P(EO- b -DMS) Homopolymer and Block Co-Oligomer Mixtures under PressureMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 18 2003Shichun Jiang Abstract The cloud-point temperatures (Tcl's) of poly(ethylene oxide) (PEO) and poly(ethylene oxide)- block -polydimethylsiloxane (P(EO- b -DMS)) homopolymer and block-oligomer mixtures were determined by turbidity measurements over a range of temperatures (105 to 130,°C), pressures (1 to 800 bar), and compositions (10,40 wt.-% PEO). The system phase separates upon cooling and Tcl was found to decrease with an increase in pressure for a constant composition. In the absence of special effects, this finding indicates negative excess volumes. Special attention was paid to the demixing temperatures as a function of the pressure for the different polymer mixtures and the plots in the T - , plane (where , signifies volume fractions). The cloud-point curves of the polymer mixture under pressures were observed for different compositions. The Sanchez-Lacombe (SL) lattice fluid theory was used to calculate the spinodals, the binodals, the Flory-Huggins (FH) interaction parameter, the enthalpy of mixing, and the volume changes of mixing. The calculated results show that modified P(EO- b -DMS) scaling parameters with the new combining rules can describe the thermodynamics of the PEO/P(EO- b -DMS) system well with the SL theory. Cloud point curves for various PEO/P(EO- b -DMS) polymer mixtures at various pressures on the T - ,PEO plane. [source] Chain Connectivity and Conformational Variability of Polymers: Clues to an Adequate Thermodynamic Description of Their Solutions, 1MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 11 2003Maria Bercea Abstract This is the first of two parts investigating the Flory-Huggins interaction parameter, ,, as a function of composition and chain length. Part 1 encompasses experimental and theoretical work. The former comprises the synthesis of poly(dimethylsiloxane)s with different molar mass and the measurements of their second osmotic virial coefficients, A2, in solvents of diverse quality as a function of M via light scattering and osmotic pressures. The theoretical analysis is performed by subdividing the dilution process into two clearly separable steps. It yields the following expression for ,o, the , value in range of pair interaction: ,o,=,,,,,,,,. The parameter , measures the effect of contact formation between solvent molecules and polymer segments at fixed chain conformation, whereas the parameter , quantifies the contributions of the conformational changes taking place in response to dilution; , becomes zero for theta conditions. The influences of M are exclusively contained in the parameter , The new relation is capable of describing hitherto incomprehensible experimental findings, like a diminution of ,o with rising M. The evaluation of experimental information for different systems according to the established equation displays the existence of a linear interrelation between , and ,. Part 2 of this investigation presents the generalization of the present approach to solutions of arbitrary composition and discusses the physical meaning of the parameters in more detail. Conformational response, ,, as a function of ,, the interaction parameter for fixed conformation. [source] Miscibility in Blends of Isotactic/Syndiotactic Polystyrenes at Melt or Quenched Amorphous Solid StateMACROMOLECULAR MATERIALS & ENGINEERING, Issue 11 2006Shu Hsien Li Abstract Summary: Miscibility in amorphous phase and behavior in a crystalline phase of blends of two semicrystalline and isomeric polymers, isotactic polystyrene (iPS) and syndiotactic polystyrene (sPS), was probed. Optical and scanning electron microscopy results indicate no discernible heterogeneity in iPS/sPS blends in either melt state or rapidly quenched amorphous super-cooled state, while the Tg behavior of the quenched amorphous blends shows an intimately mixed state of two polymer chains. The crystal forms of the blends were further analyzed to provide additional evidence of miscibility in the amorphous domain. The sPS in the iPS/sPS blends upon melt crystallization was found to predominantly exist as the more stable , -form (rather than mixed , -form and , -form in neat sPS), which also suggests evidence of miscibility in the iPS/sPS blends. The melting behavior of semicrystalline sPS in the iPS/sPS mixtures was analyzed using the Flory-Huggins approach for estimation of interactions. By measuring the equilibrium melting point of the higher-melting sPS species in the sPS/iPS blends, a small negative value, for the interaction parameter (,,,,,0.11) was found. Further, by introducing a third polymer, poly(2,6-dimethyl- p -phenylene oxide) (PPO), a ternary iPS/sPS/PPO blend system was also proven miscible, which constituted a further test for stable phase miscibility in the iPS/sPS blend. General nature of miscibility in blends composed of two crystalline isomeric polymers is discussed. Issues in dealing with blends of polymers of the same chemical repeat unit but different tacticities were addressed. X-ray diffractograms for neat sPS and iPS/sPS blends, each having been isothermally crystallized at 245,°C for 4 h. [source] Thermosensitive Poly[(2-(diethylamino)ethyl methacrylate)- co -(N,N -dimethylacrylamide)] Cryogels Prepared by a Two-Step Polymerization MethodMACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2006Tuncer Caykara Abstract Summary: Temperature-sensitive P(DEAEMA- co -DMAAm) cryogels with five different DMAAm contents were synthesized via a two-step polymerization method, the initial polymerization being conducted for various times at 22,°C, followed by polymerization at ,26,°C for 24 h. The influence of the first-step time and the content of DMAAm on the swelling ratio and network parameters such as the polymer/solvent interaction parameter, the average molecular mass between crosslinks, and the mesh size of the cryogels were reported and discussed. The swelling studies indicated that the swelling increased in the following order: 22C45,>,22C30,>,22C15,>,22C0. The cryogels exhibited swelling/deswelling transitions (reentrant phenomena) in water depending on temperature. These properties were attributed to the macroporous and regularly arranged network of the cryogels. Scanning electron microscope graphs reveal that the macroporous network structure of the cryogels can be adjusted by applying a two-step polymerization. Chemical structure of the P(DEAEMA- co -DMAAm) cryogels. [source] Formation of Two Kinds of Hexagonally Arranged Structures in ABC Triblock Copolymer Thin Films Induced by a Strongly Selective Solvent VaporMACROMOLECULAR RAPID COMMUNICATIONS, Issue 22 2009Chunxia Luo Abstract An order,order transition (OOT) in the sequence of a hexagonally arranged core,shell cylinder to a double-hexagonally arranged dot in polystyrene- block -poly(butadiene)- block -poly(2-vinylpyridine) (SBV) triblock copolymer thin films is reported to be induced upon exposure to a solvent vapor that is strongly selective for the two end blocks. These two kinds of hexagonally arranged structures could form when the film thickness is 44, 123, and 223,nm. When the film thickness is decreased to 13,nm, the ordered structure is absent. The sizes of the core,shell cylinder structures formed with the same annealing time in films of different thickness are compared to address the effects of film thickness on the phase structure. The mechanism is analyzed from the total surface area of the blocks and the effective interaction parameter in the solvent vapor. [source] Effect of Chain-Length Dependence of Interaction Parameter on Spinodals for Polydisperse Polymer BlendsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 5 2006Xiyan Du Abstract Summary: The chain-length dependence of the Flory-Huggins (FH) interaction parameter is introduced into the FH lattice theory for polydisperse polymer-blend systems. The spinodals are calculated for the model polymer blends with different chain lengths and distributions. It is found that all the related variables, rn, rw, rz, and chain-length distribution, have effects on the spinodals for polydisperse polymer blends. The spinodals at different chain lengths. [source] Pb substitution effect on the normal and superconductivity states transport of polycrystalline MgB2PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2006M. Zouaoui Abstract A series of samples of Mg1,xPbxB2 were synthesized by the conventional solid state reaction method. Its temperature dependence of resistivity was studied from the zero resistivity temperature Tc up to 300 K. In order to more understand the main reason of the decreases of Tc, we analyse the resistivity versus temperature data in the normal state using Bloch-Grüneisen formula. The Debye temperature, ,D, has been extracted from the fits. ,D is seen to decrease with the lead substitution from 1280 K to 835 K. Using ,D and Tc, the electron-phonon interaction parameter ,, has been given by McMillan equation. The values of , increase from 0.70 to 0.84 respectively for x = 0% and x = 1% sample. The decrease in Tc is argued mainly by the decrease in the density of states at the Fermi level N(EF) with Pb concentration than the decrease in ,D. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photoreflectance study of the electronic structure of Si-doped InyGa1,yAs1,xNx films with x < 0.012PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005Y.-S. Kang Abstract The electronic structure of Si-doped InyGa1,yAs1,xNx films on GaAs substrates, grown by nitrogen-plasma-assisted MBE, was examined by photoreflectance (PR) spectroscopy at temperatures between 20 K and 300 K. The measured critical-point energies were described by a band anti-crossing (BAC) model with the addition of a Burstein-Moss band-filling term. The energy difference between the nitrogen impurity level and conduction band edge was (0.3004 ± 0.0101) eV at 20 K, and (0.3286 ± 0.0089) eV at 295 K; the BAC interaction parameter was (2.588 ± 0.071) eV. It was inferred from the magnitude of the Burstein-Moss shift that the near-surface carrier concentration, probed by PR, is reduced from the bulk (Hall effect) carrier concentration by a reduction factor of 0.266 ± 0.145. The effect of strain on the PR energies was too small to observe. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Modeling the phase behavior in binary mixtures involving blowing agents and thermoplastic resins,POLYMER ENGINEERING & SCIENCE, Issue 2 2010Pedro F. Arce The thermophysical properties of mixtures of thermoplastic resins and blowing agents, together with the knowledge of the solubilities of these components, are the basis for the manufacturing of plastic foams. In this work, the solubilities of blowing agents trichlorofluoromethane, dichlorodifluoromethane, chlorodifluoromehane, and 1,2-dichloro-1,1,2,2-tetrafluoroethane in thermoplastic resins poly(styrene), high density poly(ethylene), low density poly(ethylene), poly(propylene), poly(vinyl chloride), poly(carbonate) and poly(propylene oxide) were modeled by using the Perturbed Chain-Statistical Associating Fluid Theory (PC-SAFT) and the Sánchez-Lacombe equations of state (EoS), fitting a single temperature-dependent binary interaction parameter. PC-SAFT is a theoretically based equation of state with three pure component parameters that describe efficiently the thermodynamics of complex systems. Earlier works with this EoS have already predicted the phase coexistence properties of various refrigerants and higher order alkane series compounds, along with their mixtures. The pure component parameters for the blowing agents were obtained by regression of vapor pressure and liquid density data, while the pure component parameters for the thermoplastic resins were obtained by regression of pure liquid PVT data. The parameter estimation was performed by using a modified maximum likelihood method. The solubility results obtained with both EoS have been compared; the results from PC-SAFT showed a higher accuracy in terms of solubility pressure deviations. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] The controlled release behavior and pH- and thermo-sensitivity of alginate/poly(vinyl alcohol) blended hydrogelsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 8 2009Win-Chun Jao Abstract Poly(vinyl alcohol) (PVA) was blended with sodium alginate (Alg) in various ratios and crosslinked with calcium chloride and made into hydrogel membranes. The dependence of the swelling behavior of these Alg-Ca/PVA hydrogels on pH was investigated. The temperature-dependent swelling behavior of the semi-interpenetrating network (semi-IPN) hydrogels was examined at temperatures from 2 to 45°C and the enthalpy of mixing (,Hmix) was determined at various temperatures. The molecular structure of the hydrogels was studied by infrared spectroscopy and their water structure in the semi-IPN hydrogels was measured by differential scanning calorimetry (DSC). The influence of Ca2+ content on the network structure of Alg-Ca/PVA hydrogels was investigated in terms of the compressive elastic modulus, effective crosslinking density, and the polymer,solvent interaction parameter based on the Flory theory. The loading of alizarin red S (ARS) followed the Langmuir isotherm mechanism and the release kinetics of ARS from the Alg-Ca/PVA hydrogels followed the Fickian diffusion mechanism. Copyright © 2008 John Wiley & Sons, Ltd. [source] Radiation synthesis of poly(N -vinyl-2-pyrrolidone-g-tartaric acid) hydrogels and their swelling behaviorsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 2 2002Cengiz Özyürek Abstract Poly(N-Vinyl 2-pyrrolidone-g-tartaric acid), PVP-g-TA hydrogels were prepared by ,-irradiating ternary mixture of VP/TA/Water. The influence of pH, temperature and ionic strength of swelling media on the equilibrium swelling properties of these hydrogels was investigated. Typical pH and temperature responses were observed by hydrogels such as high pH and low temperature swelling and low pH and high temperature deswelling. A change in the ionic strength of the swelling solution from 0.01 to 0.2 caused a decrease in equilibrium degree of swelling hydrogels. The average molecular weight between cross-links, Mc and polymer - solvent interaction parameter, , of PVP-g-TA hydrogels were determined according to equation recently derived by ,en and Güven for the swelling behavior of charged polymeric network. Copyright © 2002 John Wiley & Sons, Ltd. [source] Modelling and process development for gaseous separation with silicone-coated polymeric membranesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2008Xin Jiang Abstract This paper proposes a permeance equation for vapour,permanent gas mixtures in a silicone-coated polymeric membrane. The equation was derived from the Arrhenius relationship by combining an apparent activation energy and interaction parameter. Accurate values of transmembrane flux were obtained by incorporating this proposed equation, which was dependent on temperature and feed composition. The equation parameters were correlated with the experimental data of eight mixtures consisting of hydrocarbons such as ethylene, ethane, propylene and propane with nitrogen covering a broad range of temperature and concentration. A numerical integration scheme was used for developing a crossflow model utilizing the above equation, which allowed the estimation of product properties including the membrane plasticization cases. The study also reports examples of implementation of this approach in potential industrial applications for the recovery of ethylene and propylene from nitrogen. Cet article propose une équation de permeance pour les mélanges vapeur,permanents de gaz dans une membrane polymère enduite de silicone. L'équation a été dérivée du rapport d'Arrhenius en combinant une énergie d'activation et un paramètre apparents d'interaction. Des valeurs précises du flux de transmembrane ont été obtenues en incorporant cette équation proposée, qui dépendait de la composition en température et en alimentation. Les paramètres de l'équation ont été corrélés avec les données expérimentales de huit mélanges se composant des hydrocarbures tels que l'éthylène, l'éthane, le propylène et le propane avec de l'azote couvrant une large gamme de la température et de concentration. Un arrangement numérique d'intégration a été employé pour développer un modèle de croisement de flux utilisant l'équation ci-dessus, qui a permis l'évaluation des propriétés de produit comprenant les cas de plasticization de membrane. L'étude indique également des exemples d'exécution de cette approche dans des demandes industrielles potentielles de rétablissement d'éthylène et de propylène de l'azote. [source] GENETIC STUDY: FULL ARTICLE: Incorporating age at onset of smoking into genetic models for nicotine dependence: evidence for interaction with multiple genesADDICTION BIOLOGY, Issue 3 2010Richard A. Grucza ABSTRACT Nicotine dependence is moderately heritable, but identified genetic associations explain only modest portions of this heritability. We analyzed 3369 SNPs from 349 candidate genes and investigated whether incorporation of SNP-by-environment interaction into association analyses might bolster gene discovery efforts and prediction of nicotine dependence. Specifically, we incorporated the interaction between allele count and age at onset of regular smoking (AOS) into association analyses of nicotine dependence. Subjects were from the Collaborative Genetic Study of Nicotine Dependence and included 797 cases ascertained for Fagerström nicotine dependence and 811 non-nicotine-dependent smokers as controls, all of European descent. Compared with main effect models, SNP × AOS interaction models resulted in higher numbers of nominally significant tests, increased predictive utility at individual SNPs and higher predictive utility in a multi-locus model. Some SNPs previously documented in main effect analyses exhibited improved fits in the joint analysis, including rs16969968 from CHRNA5 and rs2314379 from MAP3K4. CHRNA5 exhibited larger effects in later-onset smokers, in contrast with a previous report that suggested the opposite interaction (Weiss et al. 2008). However, a number of SNPs that did not emerge in main effect analyses were among the strongest findings in the interaction analyses. These include SNPs located in GRIN2B (P = 1.5 × 10,5), which encodes a subunit of the N-methyl-D-aspartate receptor channel, a key molecule in mediating age-dependent synaptic plasticity. Incorporation of logically chosen interaction parameters, such as AOS, into genetic models of substance use disorders may increase the degree of explained phenotypic variation and constitutes a promising avenue for gene discovery. [source] Effect of magnetic Reynolds number on the two-dimensional hydromagnetic flow around a cylinderINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2009T. V. S. Sekhar Abstract Numerical experiments have been conducted to study the effect of magnetic Reynolds number on the steady, two-dimensional, viscous, incompressible and electrically conducting flow around a circular cylinder. Besides usual Reynolds number Re, the flow is governed by the magnetic Reynolds number Rm and Alfvén number ,. The flow and magnetic field are uniform and parallel at large distances from the cylinder. The pressure Poisson equation is solved to find the pressure fields in the entire flow region. The effects of the magnetic field and electrical conductivity on the recirculation bubble, drag coefficient, standing vortex and pressure are presented and discussed. For low interaction parameter (N<1), the suppression of the flow-separation is nearly independent of the conductivity of the fluid, whereas for large interaction parameters, the conductivity of the fluid strongly influences the control of flow-separation. Copyright © 2008 John Wiley & Sons, Ltd. [source] Combustion-type hydrogenation of nanostructured Mg-based composites for hydrogen storageINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2009M. V. Lototsky Abstract In this study Reactive Ball Milling in hydrogen gas was used to synthesize nanostructured hydrogenated composites of Mg and V-based alloy. After hydrogen desorption, the nanocomposites exhibited a dramatic facilitation of the rate of H absorption by Mg and reduction of the temperature of onset of hydrogenation. These favourable changes were caused by a synergy of catalytic effect of the V-based alloy on hydrogen absorption by Mg and heat release caused by exothermic hydrogen absorption by the V-based alloy. When the initial interaction temperature exceeded a threshold, rather low, value of 20,125°C, depending on the H2 pressure, composition of the sample and its total amount, a combustion-type hydrogenation took place. With optimal interaction parameters applied, H absorption was completed in just 5,70,s and was accompanied by a significant heat release. The observed features can be utilized to reach fast recharge of the Mg-based H stores and to develop efficient heat management systems. Copyright © 2009 John Wiley & Sons, Ltd. [source] Range and strength of intermolecular forces for van der Waals complexes of the type H2Xn -Rg, with X = O, S and n = 1,2INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2010Patrícia R. P. Barreto Abstract This study is intended as a continuation of previous experimental and theoretical works on the systems H2O-Rg, H2S-Rg, H2O2 -Rg, and H2S2 -Rg, where Rg = He, Ne, Ar, Kr, Xe. For the H2O-Rg and H2S-Rg systems, molecular and atomic polarizabilities have been calculated and from them, using phenomenological correlation formulas modeling the dispersion-repulsion (van der Waals) forces, the isotropic interaction parameters have been determined and compared with experimental data from this laboratory. For the H2O2 -Rg and H2S2 -Rg systems, the molecular polarizabilities have been calculated and used in correlation formulas to predict well depths and positions of van der Waals forces and a comparison made with the corresponding potential energy surfaces calculated in previous works. The approach correctly predicts the interaction parameters, except for H2O and H2O2 with the heavier rare gases. The correlation formulas have been then extended to include an attractive induction contribution accounting for the interaction between the permanent molecular dipole moment and the instantaneous induced atomic dipole moment, to improve the predicted parameters for H2O and H2O2 -Ar, Kr and Xe. The agreement with experimental and theoretical data is improved but the predicted data still underestimate the interaction. This is probably due to the presence of a significant non van der Waals contribution to the interaction for the heavier gases, as suggested by analogy with the previously studied water-Rg case. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] | ||||||||||||||||||||||