Adrián H. Buep

Dielectric properties of binary systems 10. Ideal dielectric behavior and excess dielectric properties.

Abstract A simple model is proposed to describe excess dielectric properties that is based on the additivity of electrical susceptibilities of species in a mixture. Since this requires a definition for the ideal dielectric behavior of a liquid mixture, a thermodynamicaly ideal mixture was considered to be under the effect of an applied electrical field. The resulting formalism being then independent of any particular dielectric model, as well as of the polarity of the components. The developed treatment has a general nature, is applicable to homogeneous isotropic liquid mixtures and allows to describe dielectric excesses as the sum of several contributions. Its usefulness is verified in the CCl 4 + cyclohexane, CCl 4 + benzene, CCl 4 + p-xylene and CCl 4 + toluene mixtures at 303.15 K.

Unexpected chirality in trans-1,4-dicyanocyclohexane

Abstract The experimental non-zero dipole moment of trans -1,4-dicyanocyclohexane was verified through a procedure little sensitive to solute/solvent interactions. This value cannot be explained on the basis of the generally accepted centrosymmetry for trans -1,4-derivatives of cyclohexane. NMR data of both this compound and its C-1, C-4 di-deuteroderivative, as well as semi-empirical theoretical calculations with the MNDO methods show that besides a centro-symmetric form there are also low energy stable non-centrosymmetric geometries. The latter exist as a helical deformation that can account for the non-zero value of the experimental dipole moment.

Dielectric properties of binary systems 9. Excess permittivities as the sum of several possible contributions.

Abstract A term representing rearrangements of the different species present in a binary solution was introduced in a model previously proposed. This improvement gave a good description of dielectric excesses in systems containing carbon tetrachloride + o-xylene, carbon tetrachloride + ethylbenzene at 298.15 K and 308.15 K and carbon tetrachloride + mesitylene at 293.15 K and 318.15 K.

Dielectric properties of binary systems 8. Improved model for alcohol/non polar systems.

Abstract The dielectric behavior of polar non polar liquid systems is treated as the result of associations through changes in the model proposed by Mechetti and Baron for very dilute solutions. The existence of a 1:1 interaction product (or complex) is assumed and the equilibrium constant (K) of complex formation is introduced. As a result the range of validity of the model extends into the non-dilute region and up to the limit where complexes other than 1:1 appear. These changes allow also to calculate the equilibrium constant (K) for the 1:1 complex from dielectric measurements in the dilute region. The values are in good agreement with those found in the literature.

A NEW HETERODYNE-BEAT CIRCUIT FOR THE DETERMINATION OF STATIC PERMITTIVITY

A greatly improved heterodyne‐beat oscillator was built using integrated circuits, to measure static permittivity of liquid samples. Frequency variation of the oscillator is of less than 0.7 Hz/h; that corresponds to a capacity variation of less than 0.005 pF/h. Permittivity can be measured with a precision of 0.003% and an accuracy better than 0.01%.