Polarization response of a dielectric continuum to a motion of charge
01 Jan 1995-Journal of Physical Chemistry C (American Chemical Society)-Vol. 99, Iss: 27, pp 10948-10951
About: This article is published in Journal of Physical Chemistry C.The article was published on 1995-01-01. It has received 17 citations till now. The article focuses on the topics: Dielectric & Polarization (electrochemistry).
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TL;DR: In this article, self-diffusion coefficients, D, have been measured in the glass forming liquids salol, glycerol, phenolphthaleine dimethyl ether (PDE), CDE, and ααβ-trinaphthylbenzene (TNB) in the supercooled regime.
Abstract: Self-diffusion coefficients, D, have been measured in the glass forming liquids salol, glycerol, phenolphthaleine dimethyl ether (PDE), cresolphthaleine dimethyl ether (CDE), and ααβ-trinaphthylbenzene (TNB) in the supercooled regime. The NMR static magnetic field gradient technique was applied where D >10-14 m2 s-1 can be attained. The results are similar to previous diffusion experiments where an enhancement of translational diffusion was found in comparison with rotational diffusion and shear viscosity. Various models of spatial heterogeneity are related to a phenomenological environmental fluctuation model in view of recent diffusion and relaxation data close to the glass transition.
335 citations
TL;DR: In this paper, the current understanding of experimental results regarding steady state and time dependent optical line shapes and positions is reviewed with emphasis on the relation to the macroscopic dielectric properties.
Abstract: Applying solvation dynamics experiments to viscous liquids or glassy materials near their glass transition involves long lived triplet probes, whose time dependent phosphorescence signals depend upon the local dipolar orientational dynamics, mechanical responses, and polarities. The current understanding of experimental results regarding steady state and time dependent optical line shapes and positions is reviewed with emphasis on the relation to the macroscopic dielectric properties. Several applications are discussed in detail, where advantage is taken of the spatially local instead of ensemble averaging character of this technique. These examples include studies of dynamical heterogeneity, rotational solute/solvent coupling, secondary relaxations in the glassy state, as well as confinement and interfacial effects.
116 citations
TL;DR: Time-resolved phosphorescence spectra and anisotropy of quinoxaline were measured in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-HFP), in its supercooled state near the glass-transition temperature and the effect of enhanced diffusivity was displayed.
Abstract: Time-resolved phosphorescence spectra and anisotropy of quinoxaline were measured in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-HFP), in its supercooled state near the glass-transition temperature. The solvation dynamics results are compared with the rotational motion of the probe and with the dielectric behavior of the neat ionic liquid. The dynamics in the viscous state are highly dispersive and show a super-Arrhenius temperature dependence, as typical for glass-forming materials. Combined with room-temperature results, solvation dynamics is observed to follow the structural relaxation times in terms of η/T for more than 10 decades, from subnanoseconds at room temperature to seconds near the glass-transition temperature Tg. The dielectric modulus relaxation follows this trend only for temperatures T > 1.2Tg and departs significantly from η/T in the 1.1Tg > T > Tg range. This deviation is reminiscent of the enhanced translational diffusion or fractional Stokes−Einstein behavio...
84 citations
TL;DR: By adding ions to dipolar glass formers, dielectric spectroscopy may directly couple to the translational degrees of freedom determining the glass transition, even in frequency regimes where usually strong decoupling is observed.
Abstract: We report a thorough dielectric characterization of the α relaxation of glass-forming glycerol with varying additions of LiCl. Nine salt concentrations from 0.1 to 20mol% are investigated in a frequency range of 20Hz-3GHz and analyzed in the dielectric loss and modulus representation. Information on the dc conductivity, the dielectric relaxation time (from the loss) and the conductivity relaxation time (from the modulus) is provided. Overall, with increasing ion concentration, a transition from reorientationally to translationally dominated behavior is observed and the translational ion dynamics and the dipolar reorientational dynamics become successively coupled. This gives rise to the prospect that, by adding ions to dipolar glass formers, dielectric spectroscopy may directly couple to the translational degrees of freedom determining the glass transition, even in frequency regimes where usually strong decoupling is observed.
44 citations
TL;DR: In this paper, the Stokes shift for naphthalene (≈63 cm-1) and quinoxaline (Δμ ≈ 1.3 D) was measured in n-propanol and other glass-forming solvents.
Abstract: We have measured the Stokes shift and its dynamics for the probe molecules naphthalene (Δμ ≈ 0) and quinoxaline (Δμ ≈ 1.3 D) in n-propanol and other glass-forming solvents. The Stokes shift for naphthalene (≈63 cm-1) turns out to be independent of the solvent polarity over a wide range of the static dielectric constants. Its time dependence is governed by the structural (or α- or shear stress) relaxation time of n-propanol, without any signature of the strong dielectric relaxation. For this solvent, structural and dipolar contributions can be distinguished because the time scale for dipole reorientation is a factor of 25 slower than the α-relaxation time. We conclude that the solvation of naphthalene reflects excitation-induced changes in the van der Waals interactions, which makes it an ideal probe for assessing shear stress or mechanical relaxations on microscopic spatial scales near Tg.
40 citations