On Intermolecular Dipolar Coupling in Two Strongly Polar Liquids: Dimethyl Sulfoxide and Acetonitrile

Abstract

The paper presents the results of studies of the electric and dielectric properties of dimethyl sulfoxide (DMSO) and acetonitrile (ACN), two strongly polar liquids composed of the molecules of the same dipole moment value (μ ≈ 4 D) but of a quite different static dielectric permittivity (ε(S)(DMSO) >> ε(S)(ACN)). It was shown that the activation energies for both the dc ionic conductivity (σ(DC)) and the viscosity (η) are two times higher for DMSO than for ACN; however, for both of the liquids, the temperature dependence of the product σ(DC)η is quite close to the prediction of the Stokes-Einstein relation. The dielectric results are interpreted in terms of the intermolecular dipole-dipole coupling. An exceptional behavior of DMSO most certainly results from its "monomolecularity", i.e., from the lack of the dipolar coupling in that strongly polar liquid. The effect is a consequence of a very specific structure of the DMSO molecule where its rotational dynamics makes the intermolecular dipole-dipole coupling very unfavorable, in contrast to the ACN molecules.

Effect of ionic contaminants on dielectric dispersion and relaxation processes over static permittivity frequency region in neat liquid poly(ethylene glycol)

“…1), at all the temperatures; which reveals that the ionic current in the dielectric PEG200 fulfills Ohm's law (current density is a linear function of the electric field strength). For the liquid dielectric materials of Ohmic behaviour, their dielectric loss ε″(f) spectrum presents itself, according to straight line relation ε″(f) = σ dc /2πfε 0 , where σ dc is the direct current (dc) ionic conductivity [17][18][19][20]. This behaviour is also true for the diluted electrolyte solutions [8].…”

“…As compared to the values of activation energies of small size and weakly associated dipolar liquids [18,19,25,33], significantly high values of the activation energies of PEG200 are due to its bigger molecular size, high viscosity and strong inter-molecular association. Such high values of activation energies are also reported for hydrogen-bonded supramolecular polymers of high viscosity [34,35].…”

“…This result confirms that for bigger size PEG200 system, the Stokes-Einstein law for ionic transport in viscous media having Brownian diffusion of small particles did not hold. The ion conducting liquid dipolar system, for which the Stokes-Einstein relation holds, must have temperature independent values of σ dc ⋅η product [18]. Further, the variation in σ dc ⋅ η product suggests that the ionic concentration in liquid PEG200 is also temperature dependent.…”

“…The liquid PEGs exhibit relaxation process corresponding to their molecular dynamics in the microwave frequency region [4,[13][14][15]. In the static permittivity frequency regime, PEGs and other dipolar liquids commonly exhibit ionic conductivity and electric double layers (EDLs) relaxation processes [16][17][18][19][20], and their characteristics are similar to that of the liquid polymeric electrolytes [21]. All the neat dipolar liquids possess 'natural' unidentified free ions contaminants, which are further activated by the assistance of some natural electromagnetic irradiations [19,[22][23][24].…”

Thermodynamics of Na+ Cl− ion – pair association in acetonitrile–dimethyl sulfoxide mixtures

“…It is also used as a solvent in the preparation of oligonucleotides from monomers. AN is used in the manufacture of pharmaceuticals and photographic films [9]. Acetonitrile contains hydrophobic methyl group connected to hydrophilic cyano group and thus can be thought of as an extremely small surfactant [10].…”