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  • 11
    Electronic Resource
    Electronic Resource
    Structural implications on positron lifetimes in lamellar polyethylene with chain defects (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 253-259 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: New positron lifetime data in a series of isothermally crystallized polyethylene pairs with known concentrations of chain defects, having a lamellar structure, have been measured. The materials were characterized by small-angle and wide-angle x-ray scattering techniques. Positron lifetime data were computer analyzed and only three components could be resolved. It is shown that the annihilation mechanisms can be understood in terms of average distance between lamellar crystals (long period), crystal thickness, and chain defect concentration. The present results confirm, in consonance with the conclusions of other authors, the longest component to be due to ortho-positronium pick-off annihilation. The intermediate component may be ascribed to positronium trapped at the crystal-amorphous interface. The application of a three-state trapping model yields a lifetime of about 900 ps for this state. It is suggested that the shortest component may be due to free positron annihilation, para-positronium self-annihilation, and annihilation of positrons from a tightly bound state localized at the chain defects. An approximate calculation provides lifetime values around 250 ps for this short-lived state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335720
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  • 12
    Electronic Resource
    Electronic Resource
    Relaxation behavior in model compounds of poly(aryl-ether-ketone-ketone) as revealed by dielectric spectroscopy (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 10134-10140 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The relaxation behavior of a series of ether-ketone oligomers, considered as model compounds of poly(ether-ketone-ketone), was studied by means of dielectric spectroscopy. The dynamics of the α relaxation of ether-ketone model compounds as compared with that of poly(arylether-ketone-ketone) (PEKK) (50/50), shows up differences which can be attributed to the variation of inter- and intramolecular correlations with the chain length. Model compounds exhibit a nearly similar degree of cooperativity regardless the differences in Tg values. The PEKK (50/50) polymer exhibits stronger cooperativity than the oligomers suggesting that in poly(ether-ketone-ketone)s molecular motions above Tg extend to more than one monomeric unit. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478886
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  • 13
    Electronic Resource
    Electronic Resource
    Molecular dynamics and microstructure development during cold crystallization in poly(ether-ether-ketone) as revealed by real time dielectric and x-ray methods (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 3804-3813 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The isothermal crystallization process of poly(ether-ether-ketone) from the glass has been studied in real time by dielectric spectroscopy and x-ray scattering experiments. The combination of these two techniques revealed a complete picture of the crystallization processes from the point of view of both amorphous and crystalline phases. Analysis of results shows that the sample morphology consists of lamellar stacks, separated by rather broad amorphous regions. The lamellar stacks are highly crystalline (∼70%), as obtained from both dielectric and x-ray scattering measurements, and the amorphous phase within the stacks is constrained up to a level where no segmental relaxation is possible. The remaining amorphous phase, after completion of the primary crystallization process, still has a certain mobility, but it is significantly slower than the initial amorphous mobility. Dielectric data and x-ray results are found to be highly congruent. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1388627
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  • 14
    Electronic Resource
    Electronic Resource
    The limiting size of natural paracrystals (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 521-523 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: X-ray diffraction data for various materials reveal that naturally occurring microparacrystals cannot exceed a certain limiting size. The empirically obtained linear relationship between the square root of the limiting number of lattice planes within a paracrystal and the reciprocal value of the relative distance fluctuation between planes (degree of distortion) is discussed in the light of the paracrystal approach.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889880012708
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  • 15
    Electronic Resource
    Electronic Resource
    Novel aspects of the real paracrystal (1981)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 85-91 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A revision of the mathematical concept of paracrystals is proposed. Hermann's [Z. Electrochem. (1940), 46, 425-436] early theory of mesophases represents a special case of a paracrystal where the statistical parameters introduced were merely crystalline or gas-like. The theory of paracrystals removes the black-white picture of crystalline and amorphous phases by introducing 18 new statistical parameters into conventional crystallography. It is shown that a real paracrystal can be defined by a three-dimensional convolution polynomial in combination with an empirically derived α* law. Hence, a missing corner-stone of colloid science is established.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739481000156
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  • 16
    Electronic Resource
    Electronic Resource
    Diamagnetism and structure of nitric acid-treated bulk polyethylene (1982)
    Springer
    Polymer bulletin 7 (1982), S. 317-321 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary An alternative procedure to examine the nature of the end product of nitric-acid-treated bulk polyethylene involving the measurement of the diamagnetic susceptibility is reported. This simple non-destructive method complements previous results obtained by means of IR spectroscopy. Thus after selectively removing the surface layer of the polyethylene lamellae with nitric acid (t 〉 50h) the diamagnetic susceptibility substantially decreases to values which are consistent with tilted paraffinic chains terminated by carboxyl groups including -NO2 groups in a 4∶1 ratio.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00256799
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  • 17
    Electronic Resource
    Electronic Resource
    Electrical conductivity in doped polyethylene (1981)
    Springer
    Polymer bulletin 5 (1981), S. 311-316 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Melt crystallized samples of mostly low density polyethylene were exposed to a bromine atmosphere, at room temperature, for long periods of time (3–30 h). The amount of absorbed halogen within the polymer increases with the increasing fraction of non crystalline material and decreases, while being stored in air, reaching a leveling off value. Concurrently the electrical conductivity is enhanced by several orders of magnitude depending on the proportion of absorbed dopant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00255123
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  • 18
    Electronic Resource
    Electronic Resource
    Influence of chlorosulfonation on the surface mechanical properties of lamellar polyethylene (1983)
    Springer
    Polymer bulletin 10 (1983), S. 553-557 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The hardening of lamellar polyethylene (PE) as a consequence of a controlled chlorosulfonation treatment has been studied using the microindentation technique. The hardness of the polymer turns out to be a linear function of the density of treated PE. The rate of increase is larger for samples with higher crystallinity. This increase is related to the hardening of crystal lamellae due to the surface attachment of electron dense groups. The latter impede the slippage of crystals and substantially reduce the rate of creep of the material under the contact pressure applied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00285375
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  • 19
    Electronic Resource
    Electronic Resource
    Lamellar structure in melt crystallized low density polyethylene (1984)
    Springer
    Polymer bulletin 12 (1984), S. 269-274 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary A combined X-ray diffraction and DSC investigation of the crystalline phase in lamellar low density polyethylene after conventional chlorosulfonation treatment has been carried out. Our results indicate that the acid attack does not involve any heavy group penetration within the lattice. The location of these groups at the basal crystal surface contributes, however, to an enhancement of the melting temperature of the modified lamellae. It turns out that the destruction level of crystalline material at 45°C, after 15–20 h is of the order of 20% and progressively increases for longer periods of time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00275978
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  • 20
    Electronic Resource
    Electronic Resource
    Long periods in melt crystallized polyethylene two coexisting structures? (1980)
    Springer
    Polymer bulletin 3 (1980), S. 7-12 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary New small angle X-ray diffraction data of a series of mostly low density PE samples isothermally crystallized from the melt are reported to discern between the existing ambiguities concerning the alternative of one or two lamellar periodicities. The ratio of X-ray spacings turns out to be dependent on the supercooling of the samples. This result together with the analysis of the 1st and 2nd diffraction peaks during and after heat treatments reveals that the two scattering maxima in the samples investigated most probably originate from the coexistence of two different lamellar periodicities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00263199
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