Fractional Stokes–Einstein–Debye relation and orientational entropy effects in strongly hydrogen-bonded liquid amides

Abstract

The impedance spectroscopy studies performed for two strongly hydrogen-bonded liquid amides: N-methylpropionamide (NMP, CH(3)·NH·CO·C(2)H(5)) and N-ethylacetamide (NEA, C(2)H(5)·NH·CO·CH(3)) have shown that the two centers of the peptide linkage, -NH·CO-, active in the C=OH-N hydrogen bonds formation, exhibit quite different sensibilities to the steric screening effects. In contrast to the oxygen atom, a relatively small change (CH(3)- to C(2)H(5)-) in the screening of the hydrogen atom leads to an essential decrease of the degree of the amide self-association. As a consequence, both the static dielectric permittivity and the orientational entropy increment of NEA are essentially lower than those of NMP. However, it was found that the dynamic processes studied are only weakly influenced (in the case of dc conductivity, σ(DC)) or totally not influenced (the dielectric relaxation time, τ(D)) by the different degrees of NMP and NEA self-association. The experiment shows that for both the amides, the logσ(DC) vs. logτ(D) dependence is nonlinear and can be described with the fractional Stokes-Einstein-Debye relation, σ(DC)τ ≅ const, with the exponent s varying from about -0.8 to about -0.6 in the temperature range from 5 °C to 110 °C.

Ionic conduction in binary mixtures of dipolar liquids

“…2a), which is mainly due to a large difference in ionic conductivity of Dx and the amides ( Table 1). The enhancement in σ dc from ideal behaviour of binary mixtures suggests that the hetero-molecular interactions facilitate the coupling between the Brownian translation diffusion of ions and the rotational diffusion of molecules (the Debye relaxation), which results in increase of their ions' mobility [13,14]. The excess static permittivity and effective Kirkwood correlation factor study of various binary mixtures confirmed the decrease in a number of effective parallel aligned dipoles due to heterogeneous H-bond interactions [18][19][20][21][22][23][24].…”

“…The σ dc values of an ideal binary mixture vary linearly from one constituent ionic conductivity value to the other with concentration variation [34]. The non-ideal behaviour of σ dc values against constituent concentration of some of the binary mixtures suggests that the heterogeneous molecular interactions influence the normal Brownian dynamics of relaxing molecular dipoles, which controls the ionic motion [13]. The Dx + amides mixtures have higher σ dc values from the ideal behaviour (the straight line drawn by joining the pure liquids σ dc values at X = 0 and 1) (Fig.…”

“…But the pure solvents also have significant σ dc value, which is mainly due to the free ions and electrons generated from the residual traces and thermally activated ionic impurities [11][12][13][14][15][16]. The investigations on σ dc values of pure dipolar liquids and their binary mixtures provide the information about the structural conformations and suitability in use of engineering and industrial applications [12][13][14][15][16].…”

Temperature Behavior of Electric Relaxational Effects due to Ionic Conductivity in Liquid Lactones

“…4 and 5), can be used, according to Eq. 7, for determination of the static dielectric permittivity [29,30] Finally, the complex conductivity (σ * = jωε 0 ε * ), where, in general, the real (σ ) and imaginary (σ ) parts have the form:…”

“…As was shown recently, the S (T ) dependence reflects molecular self-association such as, for example, dipolar coupling in isotropic mesogenic liquids in the vicinity of the transition to the nematic phase [37][38][39][40] or hydrogen bond formation in liquid amides [30]. The negative values of S (Fig.…”