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  • 1995-1999  (6)
  • 1965-1969
  • 1998  (3)
  • 1996  (3)
  • Polymer and Materials Science  (6)
  • 1
    Electronic Resource
    Electronic Resource
    On the correspondence between classical and quantum mechanics in macromolecular systems: Too much classical chaosResearch sponsored by the Division of Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy under contract DE-AC05-96OR22464 with Lockheed-Martin Energy Research Corp. (1998)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 7 (1998), S. 203-209 
    Details
    ISSN: 1022-1344
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In a recent study we found the classical dynamics of a polyethylene (PE) chain to exhibit low dimensional chaos at temperatures as low as a few Kelvin. These results strongly suggest that classical molecular dynamic simulations in polymer systems can grossly overestimate vibrational motion, which consequently results in disordered structures. In contrast, quantum mechanical calculations using Internal Coordinate Quantum Monte Carlo (an improved method with an initial conjecture for the correct wave function) indicate that the quantum ground state for a three-dimensional model PE chain is far more rigid than determined from molecular dynamics (MD) simulations, even at energies as low as a small fraction of the ground state energy. This result casts uncertainty on the reliability of MD estimates of dynamical or structural quantities relevant to the study of some macromolecular systems.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Surface mobility and diffusion at interfaces of polystyrene in the vicinity of the glass transition (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 567-572 
    Details
    ISSN: 0887-6266
    Keywords: surface ; interfaces ; diffusion ; polystyrene ; polyphenylene oxide ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Symmetric polydisperse (Mw = 23 × 104, Mw/Mn = 2.84) and monodisperse (Mw = 21 × 104, Mw/Mn 〈 1.05) polystyrene (PS), and asymmetric polydisperse PS/poly(2,6-dimethyl 1,4-phenylene oxide) (PPO) interfaces have been bonded in the vicinity of the glass transition temperature (Tg) of PS. In a lap-shear joint geometry, strength develops in all cases with time to the fourth power, which indicates that it is diffusion controlled. Strength developing at short times at the polydisperse PS/PS interface, at 90°C, is higher than that at the monodisperse interface, at 92°C (at Tg - 13°C in both cases), presumably due to the contribution of the low molecular weight species. The decrease of strength at the PS/PPO interface when the bonding temperature decreases from 113 to 70°C, i.e., from Tg + 10°C to Tg - 33°C of the bulk PS, indicates a high molecular mobility at the surface as compared to that in the bulk, and can be expressed by a classical diffusion equation, which is valid above Tg (of the surface layer). © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 567-572, 1998
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 3
    Electronic Resource
    Electronic Resource
    Efficient computation of potential energy first and second derivatives for molecular dynamics, normal coordinate analysis, and molecular mechanics calculationsResearch sponsored by the Division of Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy under contract DE-AC05-84OR21400 with Lockheed-Martin Energy Systems Inc. (1996)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 5 (1996), S. 771-788 
    Details
    ISSN: 1022-1344
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: By using two- and three-body internal coordinates and their derivatives as intermediates, it is possible to enormously simplify formulas for three- and four-body internal coordinates and their derivatives. Using this approach, simple formulas are presented for stretch (two-body), two types of bend (three-body), and wag and two types of torsion (four-body) internal coordinates and their first and second derivatives. The formulas are eminently suitable for economizing molecular dynamics and molecular mechanics calculations and normal coordinate analysis of complicated potential energy surfaces. Efficient methods for computing derivatives of entire potential energy terms, and in particular cross terms with switching functions, are presented.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mats.1996.040050410
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of thermal stabilizers on diffusion of poly(∊-caprolactone) in poly(vinyl chloride)/poly(∊-caprolactone) blends (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 61 (1996), S. 465-471 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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 influence of thermal stabilizers on the poly(∊-caprolactone) (PCL) diffusion in poly(vinyl chloride) (PVC)/PCL blends was studied with the addition of various concentrations of dibasic lead phthalate and dibutyltin dilaurate. The rate of PCL diffusion was followed by differential scanning calorimetry and IR spectroscopy in three series of experiments: the migration of PCL at the surface of the sample; the extraction of PCL in a fluid surrounding the sample; and the sorption of liquid PCL in the blend. In the last two series, mass losses and mass uptakes were measured as a function of time. As compared to the blend without additive, dibutyltin dilaurate induces an increase of the PCL rate of diffusion whereas dibasic lead phthalate gives a decrease. These trends are explained by: first, the formation of an associative complex between dibutyltin dilaurate and PVC, which can compete with the PVC/PCL interactions in the blend and thus favor the PCL migration; and, second, the modification of the Tg of the blend induced by the addition of a third component, which can modify the diffusion rate by changing the free volume fraction at the diffusion temperature. Tg decreases slightly in the presence of dibutyltin dilaurate but increases with dibasic lead phthalate. © 1996 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 5
    Electronic Resource
    Electronic Resource
    Carcinogenicity of CoCrMo (F-75) implants in the rat (1996)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 32 (1996), S. 37-44 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A long-term study was conducted in rats to assess the contribution of the surface area of CoCrMo devices to carcinogenesis. Groups consisting of 104 rats each (52 male, 52 female) were either implanted with metal cylinders fixed on the left, lateral femur (groups 1-3) or injected with a suspension of metal microspheres in the dorsal subcutis (group 4). Group 1 (control) received solid Ti6Al4V cylinders [surface area to body weight (SA/BW) ratio measuring 1.35 times that of human total hip prosthesis (HTHP)]. Group 2 was implanted with solid CoCrMo (SA/BW ratio: identical to implants of group 1). Group 3 received sintered-porous CoCrMo devices (SA/BW ratio: 30 × HTHP). Group 4 was injected with a suspension of CoCrMO microspheres (SA/BW ratio: 135 × HTHP). Implant-associated tumors (IATs) were observed in 23, 14, 3, and 15 rats of groups 1, 2, 3, and 4, respectively. Within groups 1 and 2, 34 IATs were associated with loose implants, three with undetermined implant fixation status, and none with fixed implants. A significantly increased accumulation of chronic inflammatory tissues around loose rather than fixed implants suggested a foreign-body reaction as the primary mechanism of carcinogenesis. A secondary role in carcinogenesis was ascribed to the increased CoCrMo implant SA/BW ratios as indicated by a 14.6% IAT incidence in group 4 versus 3% in group 3. These results support the notion that early intervention in the removal of loose metal devices is warranted to mitigate against foreign body-induced carcinogenesis, at least in this animal model. © 1996 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 6
    Electronic Resource
    Electronic Resource
    Identification and quantification of the crystalline structures of poly(vinylidene fluoride) sutures by wide-angle X-ray scattering and differential scanning calorimetry (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 39 (1998), S. 184-189 
    Details
    ISSN: 0021-9304
    Keywords: PVDF ; differential scanning calorimetry ; X-ray scattering ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The outstanding biocompatibility of the polyvinylidene fluoride (PVDF) monofilament suture together with other desirable characteristics, such as ease of handling and resistance to biodegradation, makes it an attractive alternative monofilament suture material for cardiovascular surgery. However, to achieve a high performance suture, the polymeric raw material must be exposed to different treatments, which lead to different degrees and types of crystallization. Since these crystalline modifications deeply influence the mechanical characteristics and the biostability of the sutures, the authors hereby propose a method of quantifying the different structures of PVDF using wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The commercial devices are achieved by coloring and processing the polymeric raw material. The white and unprocessed 4-0 unswaged suture presents 19% of the α phase, 38% of the β structure, and no γ form. Coloration increases the amount of the β phase by 5-9% at the expense of the α phase. On the other hand, processing the fibers lead to the conversion of some of the amorphous phase to the γ structure, the importance of which is 6-7%. Finally, tensile measurements performed on the different PVDF fibers clearly proves that their mechanical characteristics depend on the presence of these crystalline forms in the polymeric structure of PVDF. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 184-189, 1998.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
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