Comparison with Dielectric Relaxation

Nettelblad [2000] Dielectric Relaxation in Dielectric Mixtures Application of the Finite Element Method and its Comparison with Dielectric Mixture Formulas, J. Appl. Phys. 89, 8092-8100. 

E. Tuncer, S. M. Gubahski, B. Nettelblad [2001] Dielectric relaxation in dielectric mixtures Application of the finite element method and its comparison with dielectric mixture formulas, J. Appl. 

Figure 3.11 Catalytic efficiency, (fcca,/K ,)app ( ), of salt-activated subtilisin Carlsberg in hexane, THF, and acetone in comparison with T2 (transverse relaxation constant) (O) of mobile deuterons as a function of dielectric constant of solvent [103].

Comparison of the evolution of the transient absorption in pure water with the indole solution demonstrates that the dynamics of the generated elections depends on the donor molecule. The initial evolution in pure water is similar to that in indole (350 50 fs), but shows an additional contribution on a timescale of 1 - 2 ps (Fig. 2b)). The formation of electrons stemming from indole is similar to the ionization and solvation process in pure water, but the time constant corresponding to the dielectric relaxation is missing. It indicates that the electron is not completely separated from the indole cation and the interaction with the parent molecule disables the dielectric relaxation that occurs in pure water on the timescale of 1 - 2 ps. 

The variation of fanS with temperature at 1 kHz for the six poly(thiocarbonate)s is represented in Fig. 2.86. In all cases a prominent relaxation associated to the glass transition temperature labelled as a -relaxation is observed in Figure PT-1. A secondary relaxation which covers a range of about hundred degrees and which by comparison with the results reported for PCs is labeled as y relaxation. Between 80°C and 100°C a slightly dielectric activity is observed (f) zone) and at — 120°C another relaxation labelled as 5 relaxation for polymers 4,5 and 6. 

The remainder of this contribution is organized as follows In the next section, the connection between the experimentally observed dynamic Stokes shift in the fluorescence spectrum and its representation in terms of intermolecular interactions will be given. The use of MD simulation to obtain the SD response will be described and a few results presented. In Section 3.4.3 continuum dielectric theories for the SD response, focusing on the recent developments and comparison with experiments, will be discussed. Section 3.4.4 will be devoted to MD simulation results for e(k, w) of polar liquids. In Section 3.4.5 the relevance of wavevector-dependent dielectric relaxation to SD will be further explored and the factors influencing the range of validity of continuum approaches to SD discussed. 

More complicated dielectric properties may be described by superimposing such terms with different relaxation times and the corresponding values of Aco- This always results in a flattening of the dispersion curves (i.e. e and e plotted vs. log to) in comparison with the basic Debye functions of (10). 

As far as comparison with experimental data is concerned, the fractional Klein-Kramers model under discussion may be suitable for the explanation of dielectric relaxation of dilute solution of polar molecules (such as CHCI3, CH3CI, etc.) in nonpolar glassy solvents (such as decalin at low temperatures see, e.g., Ref. 93). Here, in contrast to the normal diffusion, the model can explain qualitatively the inertia-corrected anomalous (Cole-Cole-like) dielectric relaxation behavior of such solutions at low frequencies. However, one would expect that the model is not applicable at high frequencies (in the far-infrared region), where the librational character of the rotational motion must be taken... 

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