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  • 1
    ISSN: 1434-601X
    Keywords: 25.70.-z ; 25.70.Lm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Events with 2, 3 and 4 heavy-fragments (A≧20) have been detected in the reactions100Mo+100Mo atE/A =18.7, 23.7 MeV and120Sn+120Sn atE/A=18.4 MeV. The experiments were performed with an array of 12 detectors which together covered a large fraction of the forward hemisphere and allowed a high detection efficiency for these events. Masses and energies of all fragments have been reconstructed by means of an improved version of the kinematic coincidence method. The probabilitiesP 3 andP 4 of producing 3- and 4-body events were found to depend mainly on the dissipated energy rather than on the bombarding energy, thus indicating that their origin lies more in the decay properties of the excited fragments than in the dynamics of the interaction. Emission of light particles from the composite system is shown to become more relevant with increasing bombarding energy and may explain the drop of theP 3 andP 4 curves at high energy losses. Small deviations of theP 3 andP 4 curves at 23.7A · MeV from those at lower bombarding energies were used to estimate the amount of a possible pre-equilibrium light particle emission as a function of impact parameter.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: If a polymer molecule is solved within a polymer melt of the same chemical nature but of different molecular weight, the solved polymer molecule in general is expanded as compared with the unperturbed statistical coil. The expansion coefficient and the second osmotic virial coefficient depend on the molecular weights of both polymers. The experimental results follow the lattice theory for athermic solutions of polymers.
    Notes: Wird ein Polymermolekül in einer Polymerschmelze von gleicher chemischer Art aber anderem Molekulargewicht gelöst, so ist das gelöste Polymermolekül im allgemeinen relativ zum ungestörten statistischen Knäuel expandiert. Der Expansionskoeffizient und der zweite osmotische Virialkoeffizient hängen von den Molekulargewichten der beiden Polymeren ab. Die experimentellen Befunde werden durch die Gittertheorie für athermische Lösungen von Polymeren richtig beschrieben.
    Additional Material: 3 Ill.
    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
    Description / Table of Contents: With the aid of small-angle neutron scattering the molecularly disperse character of a clear mixture of two polymers in the absence of a low molecular weight compound is proved in one case and disproved in the other. If the mixture is molecularly disperse the chemical potential and the coil dimensions can be determined. Poly(methyl methacrylate) and styrene-acrylonitrile copolymers for certain compositions of the copolymer form molecularly disperse mixtures. They are exothermic, have a negative excess entropy of mixing and the coils are expanded as compared with the unperturbed coil dimensions. The theory of solubility parameters of Hildebrand and Scott enables one to find the miscible system, but the experimental second osmotic virial coefficients differ by an order of magnitude from those which could be estimated from this theory.
    Notes: Mit Hilfe der Neutronenkleinwinkelstreuung wird der molekulardisperse Charakter einer glasklaren Mischung von zwei Polymeren bei Abwesenheit eines niedermolekularen Lösungsmittels in einem Fall nachgewiesen, im anderen widerlegt. Falls eine molekulardisperse Mischung vorliegt, können das chemische Potential und die Knäueldimensionen bestimmt werden. Polymethylmethacrylat und Styrol-Acrylnitril-Copolymere bilden für gewisse Zusammensetzungen des Copolymeren molekulardisperse Mischungen. Sie sind exotherm, besitzen eine negative Exzeßentropie und die Molekülknäuel sind gegenüber den ungestörten Knäueldimensionen expandiert. Die Theorie der Löslichkeitsparameter von Hildebrand und Scott ermöglichte zwar die Auffindung des mischbaren Systems, aber die gemessenen zweiten osmotischen Virialkoeffizienten sind in der Größenordnung verschieden von denen, die nach dieser Theorie vorausberechnet werden können.
    Additional Material: 3 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: Light scattering, neutron scattering and viscosity measurements on a nematic and a smectic polymethacrylate demonstrate the presence of molecularly disperse coils in solution. For the nematic polymer, toluene is a theta solvent, the behaviour familiar from conventional polymers (unperturbed coil conformation) being exhibited at the theta point. The isotropic melts likewise contain unperturbed coils; in the case of the nematic polymers, however, the coils in the melt have a radius of gyration which is about 30% smaller than that in solution at the theta point. In the liquid-crystalline phase, the mean radii of gyration in both cases are identical to the corresponding parameters in the isotropic melt. In the nematic material, however, the coils can be shown to have a substantial anisotropy, the radius of gyration parallel to the director being about 20% smaller than that at right angles to this direction. On the basis of a theoretical chain simulation, a model for the main-chain conformation has been developed which takes into account both short-range interactions along the main chains and three-dimensional interactions by the oriented side groups. This model indicates the degree of orientation from which a change in the mean radius of gyration can be expected. Wide-angle neutron scattering experiments on smectic polymer provide information about the main-chain distribution in the smectic phase. The main chains are present in a substantially higher concentration between the smectic layers, but there are hints that they do not have a true two-dimensional arrangement.
    Additional Material: 9 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: Provided a polymer is soluble, i. e., molecularly dispersed in another polymer irrespective of the molecular weight of the components, the solution is exothermic. By increasing the temperature two effects, both unfavourable to mixing become larger: (i) the excess entropy of mixing caused by contact interaction and (ii) the total effect from the difference of the free volumes of the pure components. So, an upper miscibility gap occurs. The thermodynamic properties of the mixture cannot be derived from the properties of the pure components. They can be described by the corresponding states theory of Prigogine, Flory, and Patterson with suitable values for the contact energy and contact entropy parameters X12 and Q12. The temperature of separation can be predicted from measurements on the mixture at low temperatures.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 178 (1977), S. 1793-1810 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An improved anionic polymerization technique for the preparation of highly uniform styrene/α-methylstyrene linear two-block copolymers is described. Three sets of samples with molecular weights M were prepared under equal experimental conditions, namely polystyrenes (2 · 105 〈 M 〈 3 · 106), poly(α-methylstyrene)s (7 · 104 〈 M 〈 4 · 106), and block copolymers (2 · 105 〈 M 〈 2,5 · 106). Ultracentrifugation in a density-gradient does not show any chemical heterogeneities in the block copolymers. The molecular polydispersity U = Mw/Mn-1 is U = 0,03 or less as estimated from GPC-measurements. The high molecular and chemical homogeneity of the block copolymers and the optical similarity of the two segment types yield light scattering measurements which give molecular weights Mw, radii of gyration 〈r2〉1/2 and second virial coefficients A2 with almost the same accuracy as in the case of homopolymers. The radii of gyration and the intrinsic viscosities of the block copolymers give no evidence for any “intramolecular phase separation” in the good solvent toluene. The coil conformation corresponds closely to that of the homopolymers.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The structure and the thermodynamics of polymer blends made from two poly(styrene/acrylonitrile) copolymers with a different ratio of styrene/acrylonitrile are investigated by neutron scattering. These systems are endothermic, exhibit a positive value for the Huggins parameter χ and show phase separation at sufficiently large molecular weights. The results are in good agreement with the corresponding states theory of Prigogine and Patterson. Other polymer blends are exothermic, exhibit negative χ-values and are compatible even for infinitely large molecular weights. In these cases one can adapt the theoretical equations to the experiments by the introduction of a suitable parameter for an exothermic contact energy. This is shown for blends from poly(methyl methacrylate) and poly(styrene/acrylonitrile).
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 84 (1972), S. 769-770 
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Developing an artificial oxygen carrier for use in humans, we polymerize native haemoglobin and myoglobin, using bifunctional, amino group specific cross-linkers, to soluble, so-called hyperpolymers. These polymers, like other polymerized globular proteins, are members of a new class of macromolecues which consist of macromolecular base units. They all have, due to the mechanisms of the chemical reaction, broad distributions of molecular weights. Fractions of hyperpolymers of human haemoglobin were obtained by employing preparative gel-permeation (size-exclusion) chromatography. The calibration curve of analytical gel-permeation chromatography (GPC) for haemoglobin hyperpolymers was determined using mean molecular weights of some fractions, as assessed by osmometric and light scattering measurements. In analogy to native globular proteins, the calibration curve for haemoglobin polymers  -  within the range of molecular weights considered here, and within the experimental accuracy  -  is a straight line. All fractions of haemoglobin polymers were further characterized with the aid of calibrated analytical GPC. Mean non-uniformity was about, 0,6. The dependence of the logarithm of the intrinsic viscosity [η] on the logarithm of the viscosity-average molecular weight Mη of the fractions (the curve in the “structure-in-solution diagram”) also is a straight line, which is true for haemoglobin and for myoglobin polymers as well. Its first derivative is the exponent a of the Mark-Houwink function; for haemoglobin and myoglobin polymers the values are 0,39 and 0,46, respectively. Haemoglobin and myoglobin hyperpolymers, as members of the new class of polymers, both have a characteristic so-called “structure-in-solution diagram”, and a characteristic calibration curve in GPC. The special structure-in-solution of the polymer proteins is a novel molecular superstructure. The intrinsic viscosity for native myoglobin was found to be 3,5 mL/g.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Amorphous blends from a deuterated polyaryletherketone and a polyetherimide have been prepared and investigated by neutron scattering. The used components differ remarkably in their structure and their solution properties. The blends on the other hand are combinatorial mixtures: the scattering quantity φ1φ2/S(q) is independent of the composition of the blends if the polymer chains have the same length.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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