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  • 1
    Electronic Resource
    Electronic Resource
    Nonexponential hole burning kinetics in organic glasses (1985)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 89 (1985), S. 4569-4574 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100267a031
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  • 2
    Electronic Resource
    Electronic Resource
    Hole transport in 1,1-bis(di-4-tolylaminophenyl)cyclohexane (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 8276-8281 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Hole mobilities have been measured in vapor deposited films of 1,1-bis(di-4-tolylaminophenyl)cyclohexane over an extended range of fields and temperatures. At 295 K, the mobility is approximately 10−2 cm2/V s, the highest value for a disordered molecular solid reported thus far. Monte Carlo simulations of random walk in a geometrically and energetically disordered medium demonstrate that the time dependence of the photocurrent and the field and temperature dependencies of the mobility can be described quantitatively in terms of the inherent disorder and its effect on charge transport. No polaronic or trapping phenomena need to be invoked to reproduce even subtle features of the experimental results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460112
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  • 3
    Electronic Resource
    Electronic Resource
    Dynamics of glass-forming liquids. II. Detailed comparison of dielectric relaxation, dc-conductivity, and viscosity data (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 2043-2055 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have studied the temperature dependence of dielectric relaxation times in terms of the peak frequency fmax(T) of dielectric loss ε″(ω) and the dc-conductivity σdc(T) of several glass-forming liquids, covering 12 decades in the peak frequency fmax and 9 decades in σdc. Although dc-conductivity samples the mobility of ionic tracers, its variation with temperature is similar to that of fmax(T). The fmax(T) and σdc(T) are analyzed using the temperature-derivative method and compared to the viscosity data η−1(T). While most liquids reveal a common Vogel–Fulcher–Tammann (VFT) behavior for fmax, σdc and η−1 in an extended temperature range T≥Tm, some liquids deviate from this behavior by displaying a crossover at T=TA to an Arrhenius regime. In these cases the quantity fmax(T) decouples from the common curves for σdc(T) and η−1(T) and attains activation energies in excess (∼40% for alcohols) of those related to translational processes. For many samples a departure from the VFT behavior occurs at lower temperatures TB〈Tm which tends to retard the glass transition. The onset of this qualitative change in the temperature dependence at TB turns out to be a characteristic temperature also in other experiments. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470961
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  • 4
    Electronic Resource
    Electronic Resource
    Dynamics of glass-forming liquids. I. Temperature-derivative analysis of dielectric relaxation data (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 6251-6257 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured the dielectric relaxation times of the α process of phenyl salicylate (salol) covering 11 decades in frequency. Being representative for the class of low molecular weight organic glass forming materials, the highly resolved temperature dependence of the dynamics in salol does not follow a particular function like the Vogel–Fulcher–Tammann (VFT) law over the entire accessible range of temperatures. In order to conduct a detailed and unambiguous analysis of the temperature dependence, we take advantage of the derivatives of the experimental log(fmax) values with respect to temperature, which allow us to either linearize the frequently used temperature laws or to resolve subtle changes in fmax(T) by decreasing the number of free parameters. In this manner we observe that none of the common routes for rationalizing the dynamics like Arrhenius, VFT, Souletie scaling, and idealized mode-coupling theory account for the experimental findings properly. However, we do observe a VFT behavior within the limits 265 K≤T≤320 K, i.e., for temperatures ranging from significantly above the glass transition at Tg=220 K to far above the melting point. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469071
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  • 5
    Electronic Resource
    Electronic Resource
    Dynamics of hydrogen-bonded liquids confined to mesopores: A dielectric and neutron spectroscopy study (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 2016-2024 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we present and discuss experimental results on molecular mobility in propylene glycol and its three oligomers confined to the ∼100 A(ring) pores of a controlled porous glass. The objective is to elucidate the finite size effects on the dynamics of hydrogen-bonded liquids of different molecular weights but identical chemical composition. The methods of dielectric and neutron spectroscopy have been employed to investigate both the low- and high-frequency features as a function of temperature. We find that all fluids in pores separate into two distinct liquid phases. (i) molecules physisorbed at the surface which exhibit a dramatic frustration of their mobility related to a substantial positive shift of the glass transition temperature Tg by up to ΔTg≈+47 K; and (ii) relatively "free'' molecules in the inner pore space subject to only moderate retardation of the α and normal mode relaxation and substantial broadening of the distribution of relaxation times. The shift in Tg for the α process with ΔTg≈+5 K is maximal for the monomer liquid and gradually diminishes with increasing molecular weight or decreasing intermolecular hydrogen bonding. The inelastic neutron spectrum of confined propylene glycol shows the boson peak as expected in bulk strong and intermediate glass formers in the vicinity of Tg. This effect can be attributed to the finite-size induced crossover from long wave vibrations characteristic of a continuous medium to localized vibrations in a confined geometry. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469728
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  • 6
    Electronic Resource
    Electronic Resource
    Merocyanine-spiropyran photochemical transformation in polymers probing effects of random matrices (1988)
    s.l. : American Chemical Society
    Macromolecules 21 (1988), S. 923-929 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00182a013
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  • 7
    Electronic Resource
    Electronic Resource
    Dynamics of glass-forming liquids. IV. True activated behavior above 2 GHz in the dielectric α-relaxation of organic liquids (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 6408-6415 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured the dielectric relaxation of butylbenzene and of the glass-former propylbenzene in the frequency range 10−2 Hz to 2×1010 Hz in order to characterize the variation of relaxation times with temperature for these low loss liquids. Additionally, salol has been remeasured above 1 GHz with improved resolution. Using the sensitive data representation [−dlog10(fmaxHz)/d(1/T)]−1/2 vs 1/T we find demarcation temperatures TA, at which the temperature dependence changes from a Vogel–Fulcher type law within the limits TB≤T≤TA to Arrhenius behavior for T〉TA, corresponding to a position of the loss peak fmax〉2 GHz. The activation energies derived from dielectric relaxation data for T〉TA are associated with the energy of vaporization, Eη∝ΔEvap. A comparison of dielectric relaxation times τD to viscosity data in this wide range of temperatures suggests the relation τD∝η/T rather than τD∝η. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476063
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  • 8
    Electronic Resource
    Electronic Resource
    Dynamics of glass-forming liquids. III. Comparing the dielectric α- and β-relaxation of 1-propanol and o-terphenyl (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 1086-1093 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured the dielectric relaxation of the glass-former 1-propanol for temperatures between 65 and 350 K in the frequency range 10−2 to 2⋅1010 Hz and the photon correlation spectro-scopy decays near Tg. Attributing the strong Debye-type process of 1-propanol to distinct -OH group effects leaves two faster processes related to the structural relaxation which can be identified as α-relaxation and Johari–Goldstein type β-relaxation characteristic of nonhydrogen-bonding supercooled liquids. From the temperature dependent relaxation times τ(T) regarding the three distinct loss peaks, we can specify an α-β-bifurcation temperature Tβ, which coincides with characteristic qualitative changes in the τ(T) behavior, as also observed for ortho-terphenyl and other glass-forming liquids. This assignment is confirmed by the correla-tion times derived from incoherent quasielastic light-scattering data obtained from the simultaneously measured photon-correlation spectroscopy. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474456
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  • 9
    Electronic Resource
    Electronic Resource
    Interpretation of dispersive hole-burning kinetics (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 1743-1747 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Nonexponential decay of an ensemble of first-order processes are modeled assuming distributions of rate-controlling parameters to be responsible for dispersive kinetics. Some problems of deriving microscopic properties from experimental decay data are illustrated focusing on hole-burning kinetics on the basis of the two-level system model. This approach is compared with reasonings leading to the logarithmic decay law.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452173
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  • 10
    Electronic Resource
    Electronic Resource
    Dynamics of glass-forming liquids. V. On the link between molecular dynamics and configurational entropy (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 9016-9026 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We compare dielectric relaxation τ(T) data of several low molecular weight glass-forming liquids with the predictions of the Adam–Gibbs theory using experimental data for the configurational entropy Sc(T). Combination of Adam–Gibbs and Vogel–Fulcher equations yields an expression for Sc(T) which can be compared with experimental data. Good agreement is found for a range of temperatures near Tg〈T〈TB which depends on the fragility of the liquid and on the presence of a β relaxation. For fragile liquids, TB coincides with a qualitative change in the temperature dependence of the relaxation time scale or viscosity, with the temperature Tβ, where Johari–Goldstein-type β processes tend to merge into the α process, and with other crossover temperatures. For nonfragile liquids, TB/Tg increases, and the deviations from the Adam–Gibbs equation weaken or disappear altogether. The significance of TB, and of the Sc(T) temperature dependence implied by the Vogel–Fulcher theory fitting, are discussed in terms of the landscape paradigm. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476348
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