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  • Articles  (159)
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  • 1
    Electronic Resource
    Electronic Resource
    A nuclear magnetic resonance study of higher-order correlation functions in supercooled ortho-terphenyl (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 890-899 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using deuteron NMR techniques two-, effective three-, and various four-time correlation functions were recorded for supercooled ortho-terphenyl at 10–15 K above the calorimetric glass transition in order to characterize the heterogeneous nature of its primary response. The experimental results could successfully be described within various energy landscape models as well as via continuous time random walk simulations. These theoretical considerations provide a suitable basis for a definition of the term dynamic heterogeneity. We discuss the power but also some limitations of the present multidimensional NMR techniques when applied to amorphous materials. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475452
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  • 2
    Electronic Resource
    Electronic Resource
    Structural relaxation of the fragile glass-former propylene carbonate studied by nuclear magnetic resonance (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 9455-9462 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Proton, deuteron, and carbon NMR methods were applied to study various isotopic species of supercooled and glassy propylene carbonate. The molecular diffusion was investigated via static field gradient diffusometry and yielded evidence for a particularly pronounced enhancement of the translational over the reorientational dynamics. The latter was monitored using measurements of spin-lattice relaxation times and of two-time stimulated echoes. The sin–sin correlation functions exhibited a pronounced dependence on the evolution times. From these results it is concluded that the geometry of molecular reorientation can be described as a superposition of moderately small jump angles (about 30°) and a quasi-diffusive component which is responsible for about one-third of the total angular displacement. Finally, four-time stimulated echoes confirmed that the nonexponential relaxation in propylene carbonate is dynamically heterogeneous in nature. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481588
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  • 3
    Electronic Resource
    Electronic Resource
    Reorientations in supercooled glycerol studied by two-dimensional time-domain deuteron nuclear magnetic resonance spectroscopy (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 241-248 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The method of stimulated echoes was used to investigate the reorientational mechanism in the selectively deuterated glass-former glycerol, C3D5(OH)3 about 15 K above its calorimetric glass temperature. The reorientation process is fully isotropic. This enables an accurate determination of the decay constant, T1Q, of the quadrupolar spin order in the regime of ultraslow motion. The knowledge of this time constant has made it possible to reliably determine the rotational correlation function. The experimentally obtained evolution time-dependent correlation functions are compared with those from a simulation procedure involving a distribution of molecular jump angles. It is found that in glycerol small angles in the 2°–3° range dominate. They are accompanied by a small, but significant, fraction of larger jump angles. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476557
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  • 4
    Electronic Resource
    Electronic Resource
    Radio-frequency dielectric measurements at temperatures from 10 to 450 K (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 901-904 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A coaxial air line was constructed to connect a radio-frequency impedance analyzer and a temperature-stabilized sample holder. It is suitable for dielectric measurements in the frequency range 1 MHz–1 GHz and at temperatures between 10 and 450 K. The dielectric dispersion of Fe-doped BaTiO3 and Na-doped KCN is presented. The results demonstrate the capability of this setup when investigating materials with high as well as with low dielectric constants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342990
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  • 5
    Electronic Resource
    Electronic Resource
    Nonexponential relaxations in strong and fragile glass formers (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 4201-4209 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Deviations from thermally activated and from exponential response are typical features of the vitrification phenomenon and previously have been studied using viscoelastic, dielectric, calorimetric, optical, and other techniques. Linear response data from literature on about 70 covalent glass formers, ionic melts, supercooled liquids, amorphous polymers, and glassy crystals are surveyed. Except for orientational glasses and monohydric aliphatic alcohols a distinct but broad correlation of non-Debye behavior with non-Arrhenius relaxations is found. Within the broad trend several groups of materials, distinguished by their respective molecular complexity, can be identified and are shown to exhibit narrow correlations. At a given degree of deviation from Arrhenius behavior externally imposed stresses are relaxed with a departure from exponential behavior which is stronger the more the molecular or atomic subunits of the glassforming material are interconnected with each other.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466117
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  • 6
    Electronic Resource
    Electronic Resource
    Relaxation dynamics in molecular alloys. I. Annealed (C2F6)1−x(CClF3)x mixtures (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2143-2148 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Solid solutions of (C2F6)1−x(CClF3)x were investigated using dielectric spectroscopy. In part I of this work results on thermally equilibrated (C2F6)1−x(CClF3)x alloys are presented. The molar polarizability of liquid and plastic C2F6 was determined. The phase diagram of (C2F6)1−x(CClF3)x was studied in detail. It exhibits two eutectic points and a large miscibility gap. In a high-temperature orientationally disordered phase mixed crystals can be grown up to CClF3 concentrations x≈0.5; in the low-temperature ordered state solid solutions are stable for x≤0.25. The dielectric loss spectra indicate that in (C2F6)1−x(CClF3)x different relaxation channels are available for the CClF3 dipoles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459885
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  • 7
    Electronic Resource
    Electronic Resource
    Relaxation dynamics in molecular alloys. II. Supercooled (C2F6)1−x (CClF3)x plastic crystals (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 7397-7401 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Dielectric measurements on quenched (C2F6)1−x (CClF3)x fluorocarbon alloys are reported. In a wide concentration range, rapid cooling prevents these samples from unmixing and the plastic phase, characterized by translational order and orientational disorder, can be supercooled. The relaxation dynamics of crystals with x=0.32 is examined in detail. For temperatures below 50 K it exhibits a dominant primary and indications of secondary relaxation, i.e., typical features of glasses. The α-relaxation process is parametrized in terms of a modified Vogel–Fulcher law. Using this representation, (C2F6)0.68(CClF3)0.32 can be characterized as fragile glass according to Angell's classification scheme.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460170
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  • 8
    Electronic Resource
    Electronic Resource
    Dielectric properties of condensed fluoromethanes and fluoromethane mixtures (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 4981-4986 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Dielectric measurements were performed on liquid and solid (CF4)1−x (CMF3)x with M=H, Cl, and Br. The dielectric behavior of the polar molecules in the liquid state is well described by an Onsager equation. At the melting point, pure hydrogenated and brominated fluoromethanes condense into dipolar rigid phases, while pure tetrafluoromethane forms a plastic crystal. CClF3 exhibits dipolar relaxational phenomena in the solid state. The data indicate that near the melting point this compound is close to a transition into a plastic phase. Mixtures of CF4 with CHF3 and CBrF3 exhibit monotectic phase diagrams with a limited solubility in the liquid state and complete immiscibility in the solid state. However, formation of mixed crystals is found in (CF4)1−x (CClF3)x which exhibits a eutectic phase diagram.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455641
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  • 9
    Electronic Resource
    Electronic Resource
    Determination of trace amounts of beryllium in rocks by ion exchange chromatography and spectrophotometry (1976)
    s.l. : American Chemical Society
    Analytical chemistry 48 (1976), S. 1550-1553 
    Details
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ac50005a033
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  • 10
    Electronic Resource
    Electronic Resource
    A.c. technique for simultaneous study of local and global linear responses near the glass transition: the case of doped calcium(2+)/potassium(1+)/nitrate (1992)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 96 (1992), S. 9089-9092 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100202a001
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