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  • 1
    Digitale Medien
    Digitale Medien
    Decoupling of lithium and proton self-diffusion in supercooled LiCl:7H2O: A nuclear magnetic resonance study using ultrahigh magnetic field gradients (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 5737-5744 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Self-diffusion coefficients of lithium ions and water protons (DLi and DH) in the glass-forming electrolyte LiCl:7H2O have been measured by nuclear magnetic resonance spin-echo experiments using ultrahigh static magnetic field gradients up to 184 T m−1. The measurements were complemented by measurements of 7Li and 1H spin-lattice relaxation times. The data cover the temperature range from 313 K down to 173 K, i.e., 34 K above the glass transition temperature Tg=139 K. In this range DLi and DH change over five orders of magnitude. The self-diffusion data exhibit a strong non-Arrhenius temperature dependence which is typical for fragile glass formers. In the supercooled regime the ratio of the self-diffusion coefficients DH/DLi increases gradually with decreasing temperature, reflecting a decoupling of these diffusive modes. These results are discussed in relation to the behavior of the viscosity, electrical conductance and reorientational correlation time of water in this temperature range. It is found that lithium ion diffusion is closely coupled to these other transport processes, while proton diffusion begins to decouple at T〈1.5 Tg. Additionally, an analysis of 1H and 7Li magnetic relaxation rates 1/T1 is given. It is found that the intermolecular modes causing 1H–1H dipolar relaxation and 7Li quadrupolar relaxation also decouple from the viscosity. The results are discussed in the framework of similar phenomena observed with other fragile glasses and, more specifically, of structural changes known to occur in supercooled LiCl:H2O systems. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.472418
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  • 2
    Digitale Medien
    Digitale Medien
    Extractive crystallization of salts from concentrated aqueous solution (1991)
    s.l. : American Chemical Society
    Industrial & engineering chemistry research 30 (1991), S. 490-501 
    Details
    ISSN: 1520-5045
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1021/ie00051a009
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  • 3
    Digitale Medien
    Digitale Medien
    Pulsed photoelectron microscope for imaging laser-induced nanosecond processes (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 2456-2460 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A flash photoelectron microscope, driven by 4 ns KrF excimer laser pulses, is introduced. The microscope is equipped with a solid state laser for in situ processing of metals with focused nanosecond pulses. Transient stages during laser-induced melting, solidification, and alloying of Al films on bulk substrates have been imaged with an exposure time of 4 ns. The photoelectron microscope is proved to be a powerful real-time probe for fast-proceeding incipient laser-induced damage, sensing changes of surfaces being too shallow to be detected by light interference and electron scanning microscopy. The combined time/space resolution is limited by lens aberrations, space charge, shot noise, and detector efficiency to about 4 ns/1.3 μm, at present. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1148168
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  • 4
    Digitale Medien
    Digitale Medien
    Dielectric spectroscopy in aqueous solutions of oligosaccharides: Experiment meets simulation (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 1463-1472 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We report the frequency-dependent complex dielectric permittivity of aqueous solutions of the homologous saccharides D(+)-glucose, maltose, and maltotriose in the frequency range 200 MHz≤ν≤20 GHz. For each solute, solutions having concentrations between 0.01 and 1 mol dm−3 were studied. In all measured spectra two dispersion/loss regions could be discerned. With the exception of the two most concentrated maltotriose solutions, a good description of the spectra by the superposition of two Debye processes was possible. The amplitudes and correlation times of the glucose and maltose solutions determined from fits of the experimental data were compared to those obtained in an earlier molecular dynamics study of such systems; the overall agreement between experiment and simulation is quite satisfactory. A dielectric component analysis of the simulation results permitted a more detailed assignment of the relaxation processes occurring on the molecular level. The physical picture emerging from this analysis is compared with traditional hydration models used in the interpretation of measured dielectric data. It is shown that the usual standard models do not capture an important contribution arising from cross terms due to dipolar interactions between solute and water, as well as between hydration water and bulk water. This finding suggests that conventional approaches to determine molecular dipole moments of the solutes may be problematic. This is certainly the case for solutes with small molecular dipole moments, but strong solute–solvent interactions, such as the saccharides studied here. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1380205
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  • 5
    Digitale Medien
    Digitale Medien
    Ion pair correlations near critical points of ionic fluids: Experimental investigation of the static permittivity (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 5273-5276 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We report on data for the concentration dependence of the static dielectric constant cursive-epsilonS of solutions of tetra-n-butylammonium naphtylsulfonate (TBNAS) in toluene derived from measurements of the frequency-dependent complex permittivity. The system shows an upper consolute point at Tc=329 K and a mole fraction Xc=0.0235 of the salt. The measurements were performed along a slightly supercritical isotherm at 338.15 K at mole fractions 0.01≤X≤0.068. cursive-epsilonS increases with increasing salt concentration. At the critical point cursive-epsilonS=(3.1±0.05) compared with cursive-epsilonS=2.35 for pure toluene. In the concentration range covered by the experiments, the effective dipole moments calculated from these data are of the order of μeff=5 D, which is distinctly lower than an estimate for the isolated molecule, μ0≅18 D. The difference is attributed to compensation effects due to preferred antiparallel ion pair orientations, as described by a Kirkwood–Fröhlich-type theory with correlation factors of gK〈1. At the critical point we find gK≅0.05. Due to these orientational correlations, dipole–dipole interactions between ion pairs may provide a significantly smaller contribution to the free energy than predicted by theory. This may explain the good performance of theories that ignore dipole–dipole interactions between pairs. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1349093
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  • 6
    Digitale Medien
    Digitale Medien
    The effect of site-specific isotopic substitutions on transport coefficients of liquid methanol (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 2568-2574 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A new approach is suggested for studying the nature of molecular transport in simple liquids, which makes use of site-specific isotopic substitutions. Its application represents the first systematic experimental study of a theoretically predicted correlation between transport coefficients in liquids and molecular moments of inertia. For this purpose, we have determined the viscosities and self-diffusion coefficients at 25 °C of normal methanol and seven isotopically labeled methanol species: CH3OD, CD3OH, CD3OD, CH2DOH, CHD2OH, CHD2OD, and 13CH3OH. Except for 12C/13C substitution, the observed isotope effects are significantly larger than predicted by a square root of mass dependence, but are well correlated with the square roots of the moments of inertia. The results give strong evidence that translation–rotation coupling influences the transport processes in methanol, thus confirming earlier interpretations of isotope effects upon the transport in water.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.457016
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  • 7
    Digitale Medien
    Digitale Medien
    Near-critical light scattering of an ionic fluid with liquid–liquid phase transition (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 848-851 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We report on the first static and dynamic light scattering measurements of near-critical behavior of an ionic fluid. The model system tetra-n-butylammonium picrate-tridecanol exhibits a liquid–liquid phase transition with an upper critical point near 342 K. The correlation lengths and scattering intensities scale with temperature corresponding to mean-field behavior. The data are also concordant with nonclassical 3D-Ising exponents if suitable Wegner corrections are applied. The spherical model recently suggested to apply for ionic fluids can be ruled out, thus resolving a current controversy in the literature.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.462416
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  • 8
    Digitale Medien
    Digitale Medien
    Anisotropic molecular reorientation of liquid benzene revisited. A study using 13C magnetic relaxation through chemical shift anisotropy and spin rotation (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3361-3365 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We report on 13C magnetic relaxation in liquid benzene (C6H6 and C6D6) at 293 K at resonance frequencies of 22.63 and 100.6 MHz. The total spin–lattice relaxation rates are separated into contributions from 13C–1H and 13C–2D dipolar, spin–rotation (SR), and chemical shift anisotropy (CSA) interactions. As the principal axis of the 13C chemical shift tensor is collinear with the sixfold axis of benzene, CSA relaxation provides information on the tumbling motion of benzene, hitherto not available from other NMR experiments. The resulting correlation time τ⊥ = 1.63 ps at 20 °C indicates a faster tumbling motion, and hence, a smaller anisotropy of benzene reorientation than usually quoted in the literature. This result is qualitatively confirmed by an analysis of 13C relaxation by SR interaction, and is in fair agreement with recent results obtained in Raman line shape measurements. It is, however, at variance with the figures deduced from Rayleigh scattering experiments. The activation energy for the tumbling motion is found to be 9.8 kJ mol−1, which is markedly larger than the activation energy of 7.7 kJ mol−1 obtained from 2D relaxation data for the motion of in-plane axes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.459759
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  • 9
    Digitale Medien
    Digitale Medien
    Ion pairing and redissociation in concentrated aqueous solutions of 2:2 electrolytes: a transport coefficient study of aqueous zinc sulfate (1991)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 95 (1991), S. 8933-8938 
    Details
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1021/j100175a092
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  • 10
    Digitale Medien
    Digitale Medien
    (P,T,x) Surface of liquid-liquid immiscibility in aqueous solutions of tetraalkylammonium salts (1992)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 96 (1992), S. 2407-2409 
    Details
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1021/j100185a004
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