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  • 1
    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 renormalization group technique, developed in the mean field theory, is applied here as a method for calculating of elastic or viscoelastic properties of heterogeneous materials with complex structures. The method consists in averageing of properties of small volume elements of the heterogeneous system by step-wise application of a recurrence relation which renormalizes properties of the group of neighbouring cells to properties of a new cell of larger dimensions. The recurrence relations are derived on the basis of the “packet” model — a group of eight elemental cells.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1435-1528
    Keywords: Relaxation mechanism ; polymer melts ; viscoelastic properties ; star polymers ; microgels ; polyisoprene ; polybutadiene ; block copolymers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Dynamic behavior of various polymer melts is studied on the basis of a comparison of viscoelastic properties with the information obtained from dielectric spectroscopy. The experimental observations are compared with results of computer simulation of corresponding systems. The studies include simple melts of linear chains, block copolymer systems of miscible components, as well as the behavior of melts with molecular objects of complex topology-like stars or microgels. In the case of polyisoprene linear chain melts an equivalence of terminal relaxation times determined from mechanical and dielectric measurements is demonstrated. Using linear block copolymers of isoprene and butadiene, relaxation times of chain fragments (isoprene blocks) in relation to relaxation times of whole copolymer chains are determined and compared with theory and simulation. Both the experimentally determined block relaxation times and relaxation times of chain fragments in simulated linear chain melts show a disagreement with predictions of the reptation theory. In the case of multiarm star polymers and microgel melts, the slow relaxation modes observed in viscoelastic spectra are assigned to cooperative translational motions detected in corresponding simulated systems in which an ordering of such molecules is demonstrated. This suggests that the terminal relaxation in multiarm star or microgel melts is governed by another relaxation mechanism than in linear chain melts. High efficiency of the Cooperative Motion Algorithm in simulation of dense systems of complex molecules is demonstrated.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The discotic liquid-crystalline polymers poly[oxy(3,7,10,11-tetrapentoxy-2,6-triphenylenediyl)-oxycarbonyltetradecamethylenecarbonyl] (1), containing discotic mesogenic groups in the main chain and poly[methyl(3,6,7,10,11-pentapentoxy-2-triphenylenyloxyundecyl)siloxane] (2) with disc-like groups attached to the polymer chain by flexible spacers, are studied by X-ray diffraction, solid-state nuclear magnetic resonance, differential scanning calorimetry and dynamic mechanical measurements, in order to determine the dynamic and structural transitions. It is shown that low-temperature softening in both polymers is caused by the mobility of short aliphatic side chains attached to the discotic units. Once formed, the columnar mesomorphic structure is stable up to the temperature of isotropization. For the main-chain polymer, a third transition is observed in samples quenched from the melt. The transition is related to the mobility of the main chain in an amorphous structure, where the discotic units are not organized in columns.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of rigid-rod polyesters with flexible alkoxy side chains of different length has been studied in order to determine the structure and properties of the polymers in various states (solid state, mesophase, melt). Various supermolecular structures can be obtained depending on the length of the side chains and on the preparation conditions of the samples. The relaxation behavior of the polymers has been investigated by dynamic mechanical measurements. Complex relaxation spectra have been observed, and types of molecular motions and structural rearrangements have been assigned to the observed mechanical relaxation transitions. The rheological behavior was studied in the mesophase and in the melt. In some polymers typical liquid-crystalline properties have been observed, as for example the flow-thinning effect. Large deformation of polymer films as well as the structure and mechanical strength of oriented samples have also been studied.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of polyesters based on 2′,5′-dihexyl-p-terphenyl-4,4″-diol as one component and various aliphatic or aromatic diacids as the second component have been synthesized. The polyesters are soluble and film forming. Materials based on the terphenyldiol and terephthalic acid or the terphenyldiol and 2′,5′-dihexyl-p-terphenyl-4,4″-dicarboxylic acid show a temperature dependence of the elastic modulus between 100 and 300°C resembling the behavior of hard elastic polymers, Glass transition phenomena in the conventional sense were not observed. The materials exhibit good mechanical properties up to temperatures well above 300°C.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The physical structure of semicrystalline polymers influences many of their properties. It has been shown that thermal treatment (rate of cooling and annealing) as well as the action of mechanical forces (drawing) of isotactic polypropylene (PP) resulted in materials with different mechanical properties. In the case of isotropic films the crystallization temperature or annealing temperature from the glass and consequently morphological structure which has been formed, determine the values of modulae, yield stress and viscoelastic properties. Reoptical behaviour has been found to be sensitive to structural differences too. The structure and mechanical properties of highly oriented PP samples which have been obtained by drawing through a flat die have been found to be dependent on parameters characterizing this process (drawing rate, apex angle of die and elongation ratio).
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 2401-2410 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Liquid-crystalline polymers with mesogenic groups in the main chain and side chains as well as their networks are studied by the dynamic mechanical method. The homopolymers are compared with chiral copolymers of a similar chemical structure. Mechanical relaxation transitions are correlated with transitions observed by differential scanning calorimetry. In the nematic phase a flow-thinning effect has been observed both for uncrosslinked polymers and for crosslinked systems. A possible molecular interpretation of the observed mechanical behaviour is discussed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Basel : Wiley-Blackwell
    ISSN: 0173-2803
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 2676-2680 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: At present the collective motion algorithm is the only Monte Carlo technique which allows the simulation of monodisperse polymer melts on a lattice at a volume fraction of unity. Here we describe the algorithm in detail and show that it fulfils the condition of detailed balance. It yields chain dimensions which are slightly smaller than chain dimensions obtained for polydisperse systems or for systems at volume fractions smaller than unity, as expected. The computational expense to obtain an independent sample containing a constant number of chains increases as about the 3.6th power of chain length.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 3548-3553 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present computer simulations of dense polymer mixtures composed of flexible and semiflexible chains. It is found that a demixing transition takes place below a certain degree of flexibility, even without introducing repelling interactions between the two polymers except the excluded volume condition. Computing the equilibrium concentration of phases for various temperatures, a phase diagram for the binary mixture is found. The results show qualitative agreement with the Flory lattice theory of stiff chains.
    Type of Medium: Electronic Resource
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