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  • 1
    Electronic Resource
    Electronic Resource
    Chain dynamics and conformational transition in cis-polyisoprene: Comparison between melt and subglass state by molecular dynamics simulations (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 4433-4443 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular-dynamics simulations are performed to analyze the local chain dynamics of cis-1,4-polyisoprene at various temperatures. The volumetric glass transition was found at around 247 K. The torsional angle autocorrelation functions (TACF) for the three kinds of backbone chain and the orientation autocorrelation functions (OACF) for bond vectors in skeletal and side chain were analyzed both near the chain ends and in the middle of the chain. Various types of cooperative conformational jumps (and librations) were found in the melt chain. However, the cooperative counter-rotation at second-neighbor single bond pairs, HC–CH2 and CH2–C, became a major correlation as the temperature decreased to the subglass region. Even in the subglass chain at 173 K, more than 30% bond pairs showed cooperative counter-rotation at the second-neighbor (Group A) under the conditions in which about 60% of the bond pairs showed no conformational jump (Group B) during 20 ns molecular dynamics (MD) runs. The TACF decays for the torsions in Group A were highly different from those in Group B. In contrast, the OACF decays for the classified C–CH3 vectors next to Group A showed no difference from that next to Group B. These findings indicated that the cooperative transitions at the second-neighbor were only a short-range correlation on the single bond pairs without changing the reorientation of the two double bond planes next to the single bond pairs. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288023
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular dynamics simulation of water diffusion in atactic and amorphous isotactic polypropylene (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 3001-3009 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics (MD) simulation of the diffusion of water in both atactic polypropylene (aPP) and amorphous isotactic polypropylene (iPP) models has been performed. Constant particle number, constant pressure, and constant temperature (NPT) MD was employed for both systems consisting of three polypropylene chains of 500 monomer units with ten water molecules. The density observed for the iPP model after full equilibration was slightly greater than that for the aPP model, but predicted x-ray scattering curves indicated that both systems were completely amorphous structures. In the aPP model, time duration up to 11 ns showed that the water molecules dynamically came together forming a water cluster with various sizes and again departed to a smaller size cluster or a single water sometimes. In contrast, the clustering was remarkable in the iPP model and maintained its aggregated structure over several nanoseconds. The self-diffusion coefficient, Dself, estimated from the mean-square displacement curve for the aPP model and the iPP one up to 11 ns duration showed 2.2×10−6 cm2/s and 3.1×10−7 cm2/s, respectively. The latter value corresponded well to the range of experimental diffusion coefficients. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475686
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  • 3
    Electronic Resource
    Electronic Resource
    Solubilities of small molecules in polyethylene evaluated by a test-particle-insertion method (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 478-486 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Free-energy related properties for penetrant sorption (water, methane, argon, oxygen, nitrogen, ethane, propane, and carbon dioxide) in amorphous polyethylene have been evaluated by a test-particle-insertion method with the excluded volume map sampling (EVMS). Two model systems, one a long chain model composed of 4 linear chains each having 1002 carbon atoms and another a short chain model composed of 167 molecules of C24H50, were compared in relation to the penetrant solubility at 298 K. The time-dependent molecular configurations were obtained by a molecular dynamics (MD) simulation under constant particle number, constant pressure, and constant temperature (NPT) conditions. The solubility coefficient obtained by the EVMS method was larger in the order, C3H8〉C2H6〉CO2〉CH4〉Ar〉O2〉N2, similar to the experimental results, and the absolute values were also in agreement with the experimental value. In the long chain host-molecules, reflecting the higher density, the solubility was about 0.85–0.90 times smaller for most penetrants tested, while ethane and propane showed higher solubility in contrast. Analysis of the averaged unoccupied volume fraction and their distribution in both systems revealed that big holes, in which a sphere with a diameter larger than 5.0 Å can be introduced, were formed in the long chain model irrespective of the denser structure. These findings resulted in higher solubility of a larger penetrant such as ethane and propane in the long chain matrix. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480594
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  • 4
    Electronic Resource
    Electronic Resource
    Clustering of water in polyethylene: A molecular-dynamics simulation (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 6476-6485 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular-dynamics (MD) simulation of the diffusion of water in amorphous polyethylene has been performed under a constant particle number, constant pressure, and constant temperature (NPT) conditions. The three simulation systems with the different water concentration from 0.120% (g/g) to 0.324% (g/g) were tested. A time duration beyond 10 ns at 298 K and at 0.1 MPa revealed that the system retained the amorphous structure and the water molecules came together forming water clusters of various sizes. The amount of water clustering depended on the water concentration and we observed irreversible clustering of a large cluster over 18 ns duration in the system with higher concentration. The oxygen–oxygen, hydrogen–hydrogen, and oxygen–hydrogen radial distribution function in a ten-water cluster showed that the position of the first and second peaks were quite similar to those of liquid TIP4P water, indicating the liquidlike structure of clustered water. As the self-diffusion coefficients, Dself, greatly depended on the time range used, the mutual-diffusion coefficients, Dmutual were also evaluated from the mean-square displacement of the center of mass of all water molecules. The Dmutual values were not so time dependent, and the values around 1×10−6 cm2/s were qualitatively comparable to the experimental values. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477293
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  • 5
    Electronic Resource
    Electronic Resource
    Molecular-dynamics simulation of moisture diffusion in polyethylene beyond 10 ns duration (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 2149-2159 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular-dynamics (MD) simulation of the diffusion of water in amorphous polyethylene has been performed. In order to obtain information about the fundamental diffusion behavior of water, the constant particle number, constant pressure, and constant temperature (NPT) MD was employed for three model systems differing in the number of water molecules and methylene group in the polyethylene chains. Time duration beyond 10 ns showed that the water molecules came together forming water clusters of various sizes. Although the self-diffusion coefficient Dself estimated from the mean-square displacement curve scattered considerably in the order from 10−8–10−5 cm2/s, Dself for the water cluster is generally one order lower in magnitude than that of a single water. However, the linearity of the mean-square curve for the larger system which contained 4000 carbon atoms was very good, and Dself obtained for ten water molecules up to 11 ns duration showed 7.1×10−7 cm2/s which was in good agreement with the experimental value. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474564
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  • 6
    Electronic Resource
    Electronic Resource
    Acetylcholine suppresses the spread of excitation in the visual cortex revealed by optical recording: possible differential effect depending on the source of input (1999)
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 11 (1999), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Optical recording with a voltage-sensitive dye was performed in visual cortical slices of the rat to determine the effect of acetylcholine (ACh) on the spread of excitation. In the presence of ACh, the spread of excitation initiated by stimulation at the white matter/layer VI (WM/VI) was greatly suppressed throughout the cortex, with less suppression in the middle layers. By comparing the effect of ACh with that of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), the fraction of the synaptic component that was sensitive to ACh was evaluated. ACh suppressed ∼ 40–50% (maximum 55.8%, n = 11) of the initial synaptic component in the superficial and deep layers. In the middle, however, the effect was weakest and only ∼ 20–30% (minimum 20.9%, n = 11) of the initial synaptic component was suppressed. On the basis of histological analysis, the region with the weakest ACh effect extended from upper V to lower II/III. To identify the site of ACh action in terms of pre- versus postsynaptic localization, exogenous glutamate was applied. Because ACh did not suppress the excitation induced by glutamate, the site of the ACh action was indicated to be presynaptic. When layer II/III was stimulated instead of WM/VI, the suppression was uniform throughout the cortex. A muscarinic receptor antagonist, atropine, blocked the suppression by ACh. In conclusion, our results indicate the following two points. First, ACh strongly suppresses intracortical connectivity through presynaptic muscarinic receptors. Secondly, in contrast to the intracortical connection, some group(s) of fibres, possibly thalamocortical afferents that arise from white matter and terminate in the middle cortical layers are suppressed much less by ACh. While ACh has been reported to have confusingly diverse effects, e.g. direct depolarization and hyperpolarization as well as synaptic facilitation and suppression, its effect on the propagation of excitation is very clear; suppression on intracortical connection, leaving thalamocortical inputs rather intact. We postulate that cholinergic innervation enables the afferent input to have a relatively dominant effect in the cortex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1460-9568.1999.00779.x
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  • 7
    Electronic Resource
    Electronic Resource
    Diffusion of low molecular weight substances into a laminar film. I: Rigorous solution of the diffusion equation in a composite film of multiple layers (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 709-721 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A rigorous solution of the diffusion of penetrant into a laminar film comprised of multilayers of m components is presented by an orthogonal-expansion method. As the simplest practical cases of m - 2 and m - 3, with stepwise distribution of both diffusion coefficients and solubility coefficients at the boundary between respective layers, the diffusion properties in the transient state are analyzed in detail. That is, changes in the penetrant concentration distribution within the laminar film and the total amount of penetrant sorbed within the film both with time after exposing the film to an atmosphere of fixed penetrant concentration are calculated for A-B as well as A-B-A type layer arrangements. The calculation is performed while keeping (L2/L1) at a constant value of 2.0 but varying the diffusion coefficient ratio of (D1/D2) from 102 to 10-2, and/or varying the solubility coefficient ratio of (S1/S2) from 1 to 10, where L1 and (L2 - L1) are the thickness D1 and D2 are the diffusion coefficients of penetrant, and S1 and S2 are the solubility coefficients in the A-component and B-component, respectively. The sorption curves deviate considerably from those of Fickian curves of homogeneous film with (D1/D2) - 1 in their respective ways. The results obtained here can be applied to the diffusion in a single component polymer film having a surface layer with different diffusion properties from that of the inner side of the film caused by differing distributions in molecular orientation or degrees of crystallinity.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760350811
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  • 8
    Electronic Resource
    Electronic Resource
    Diffusion of low molecular weight substances into a fiber with skin-core structure - rigorous solution of the diffusion in a coaxial cylinder of multiple components (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 330-340 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The diffusion equation of low molecular weight substances (penetrant) into a coaxial cylinder of multiple components (m) was formulated in general and solved rigorously. As the simplest but a practical case of m = 2, which corresponds to the diffusion of penetrant into fibrous material with skin and core structure, the diffusion of penetrant was analyzed in detail. That is, changes in the penetrant concentration distribution within the coaxial dual cylinder of skin and core components and the total amount of penetrant sorbed within the cylinder both with time after exposing the cylinder to atmosphere of fixed penetrant concentration of Cout were calculated with variation of the diffusion coefficient ratio (D1/D2) and the radius ratio (R2/R1), where D1 and D2 are the diffusion coefficients of penetrant in the core and the skin, and R2 and R1 are the radii of the fibrous material and the core, respectively. Keeping (R2/R1) at a constant value of 1.2 but varying (D1/D2) from 104 to 10-2, the penetrant concentration distribution was calculated and found to be much different particularly within the core between (D1/D2) 〉 1 and (D1/D2) 〈 1. The sorption curves were also found to deviate in their respective ways from that of Fickian curve of a homogeneous cylinder with (D1/D2) = 1 except at initial stage of sorption. Further, by keeping (D1/D2) constant but varying (R2/R1) from 1.1 to 1.5, the effects of relative skin thickness upon the sorption curve were studied.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340415
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  • 9
    Electronic Resource
    Electronic Resource
    Moisture sorption mechanism of aromatic polyamide fibers. V: Growth of crystallites in as-spun wet poly(p-phenylene terephthalamide) fiber during dehydration (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 1423-1432 
    Details
    ISSN: 0887-6266
    Keywords: crystallite ; Kevlar ; moisture sorption ; poly(p-phenylene terephthalamide) ; wide-angle x-ray diffraction ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Wide-angle x-ray diffraction studies were performed for as-spun wet poly(p-phenylene terephthalamide) fiber. The effects of sorbed water on the equatorial diffractions from the (110) and (200) crystal planes and on the meridional diffractions from the (002), (004), and (006) crystal planes were analyzed during desorption and absorption. There was no significant change in the d-spacing from the respective crystal plane irrespective of the moisture (water) regain. The ratio of the diffracted intensity from the (110) diffraction to that from the (200) diffraction remarkably increased by removing the sorbed water. The crystallite size estimated from the (110) diffraction, L110, also increased as the moisture regain decreased, while the L200 did not increase. The longitudinal size of paracrystallite, D001, also remarkably increased with the decrease in moisture regain with the lattice distortion factor, gII, kept unchanged. These results strongly suggested the growth of the crystallite via hydrogen bonds in the lateral (b-axis) direction. The growth of the lateral size of crystallite also accompanied the longitudinal growth of crystallite during desorption. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1423-1432, 1997
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Rheo-optical properties of polyethylene films in the nonlinear viscoelastic region (1989)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 27 (1989), S. 2283-2293 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A new apparatus was designed to investigate the dynamic viscoelastic properties of solid polymer materials in the nonlinear viscoelastic region. The apparatus was combined with a birefringence apparatus in such a way that birefringence could be measured simultaneously with stress under oscillatory deformation. The nonlinear viscoelastic behavior of bulk-crystallized high-density polyethylene films was examined. Nonlinearity of mechanical properties became evident around 30°C, while optical properties became markedly nonlinear around 50°C. The nonlinearity of viscoelastic properties changes very little when the films are swollen with tetrachloroethane. It is proposed that disruption of lamellae to crystallites in the drawing process is one of the most important causes of the nonlinear behavior of high-density polyethylene films.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1989.090271110
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