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  • 1
    Digitale Medien
    Digitale Medien
    Effects of radiation on mechanical properties of polybutadiene/polystyrene blends (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 58 (1995), S. 85-94 
    Details
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Blends containing 3 wt % low molecular weight polybutadiene (PB) in a polystyrene (PS) matrix were prepared via a precipitation technique that yielded spherical, submicron pools of PB. Tensile specimens made from these blends were then irradiated with high energy electrons in air at dose levels from 0 to 70 Mrads. The blends, which previously showed high levels of toughness approaching that of high impact PS, lost all enhanced toughness when irradiated above 10 Mrads. Analysis of pure PS specimens irradiated over the dose range from 0 to 45 Mrads showed no appreciable dependence of mechanical behavior on dose level. Molecular weight studies of the polybutadiene demonstrated only a very modest increase in molecular weight in the dose range studied here; therefore, reduced mobility of the PB in the blends was not the reason for the dramatic drop in toughness with radiation dose. It was concluded that radiation-induced scission of the PS near the surface of the blends resulted in a significant local reduction in molecular weight. This degraded layer led to premature craze failure and hence a low level of toughness. It was demonstrated that the absence of oxygen during the irradiation process or the removal of the scissioned surface layer via mechanical abrasion resulted in a recovery of toughness. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/app.1995.070580109
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  • 2
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: 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.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: 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.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): PVDF ; differential scanning calorimetry ; X-ray scattering ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: 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.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Variation in PED response at a gold microelectrode as a function of waveform parameters when applied to alditols and carbohydrates separated by capillary electrophoresis (1995)
    Weinheim : Wiley-Blackwell
    Electroanalysis 7 (1995), S. 1015-1019 
    Details
    ISSN: 1040-0397
    Schlagwort(e): Capillary electrophoresis ; Pulsed electrochemical detection ; Alditols ; Carbohydrates ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Results are presented from a systematic study of the noise (N) and peak-to-noise ratio (P/N) obtained for pulsed electrochemical detection (PED) at a gold micro-wire electrode applied to a mixture of alditols and monosaccharides separated by capillary electrophoresis (CE). The electrode potentials and time periods for oxidative cleaning and reductive reactivation of the electrode were held constant in the PED waveform at minimum allowable values and the time period for digital integration of electrode current (tint) was varied from 50 to 800 ms by 50-ms intervals. The value of N was virtually independent of tint and P/N increased approximately as a linear function of tint in the range 50-200 ms corresponding to waveform frequencies in the range 4.5-2.7 Hz. A detection limit of 9 fmol glucose was determined for a 4-nL injection using tint = 200 ms.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/elan.1140071104
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  • 6
    Digitale Medien
    Digitale Medien
    Metal nanoparticle/polymer superlattice films: Fabrication and control of layer structureWe gratefully acknowledge support for this work from the Office of Naval Research under the Molecular Engineering Accelerated Research Initiative, the University Louis Pasteur, the Centre Nationale de la Recherche Scientifique, and from the Deutsche Forschungsgemeinschaft. We thank Dr. Moog Chow for assistance with transmission electron microscopy characterization of the Au colloids and Prof. Dr. H. Mohwald for helpful discussions. (1997)
    Weinheim : Wiley-Blackwell
    Advanced Materials 9 (1997), S. 61-65 
    Details
    ISSN: 0935-9648
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/adma.19970090114
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  • 7
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): surface ; interfaces ; diffusion ; polystyrene ; polyphenylene oxide ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: 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
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Recent advances in polymer molecular dynamics simulation and data analysisResearch 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. (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 6 (1997), S. 855-880 
    Details
    ISSN: 1022-1344
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Significant advances in molecular simulation methodology over the past decade have greatly reduced the traditional size-timescale bottleneck in molecular dynamics calculations. The development of the geometric statement function method allows for systems up to several hundred thousand atoms to be simulated for up to several nanoseconds in reasonable times on standard workstations. For constant energy simulations, the use of symplectic integrators ensures accurate dynamics, even at long simulation times, without velocity or other artificial rescaling schemes. Finally, new methods of frequency estimation allow for accurate vibrational mode frequency calculations even in the presence of chaotic motion on time scales twenty times shorter than the standard fast Fourier transform, with an additional improvement in the sensitivity of the results when initial dynamics conditions are carefully chosen.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mats.1997.040060501
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  • 9
    Digitale Medien
    Digitale Medien
    Molecular dynamics treatment of torsional interactions accompanied by dissociationResearch sponsored by the Division of Chemical Sciences, Office of Basic Energy Science, U.S. Department of Energy under contract DE-AC05-84OR21400 with Martin Marietta Energy Systems Inc. (1995)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 4 (1995), S. 909-920 
    Details
    ISSN: 1022-1344
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: When three atoms in a bend sequence move into a linear configuration, any torsional angle involving those three atoms becomes undefined and its Cartesian derivatives singular. In molecular dynamics simulations, this is most likely to occur during and after a bond-breaking process, leading to spuriously large torsional forces and energies which invalidate the simulation. By including appropriate bend angle switching functions in torsional interaction terms, one may approach the linear bend limit in a well-defined manner and make torsional forces vanish around this limit, as expected on physical grounds. Although this expense can be greatly reduced by observing that any internal force must not move the center of mass of the particles involved. Several approximations explored in this paper can reduce this effort even further.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mats.1995.040040504
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  • 10
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: 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.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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