The Frequency Variation of the Dielectric Constant of Dilute Non-Aqueous Solutions

Abstract

For systems containing polar molecules it has been found that there is a wave-length region in which the dielectric constant decreases with increasing frequency. This wave-length region, dependent upon the size of the orienting molecule and the viscosity of the medium, determines a time of relaxation for the polar molecules which has been evaluated by Debye using the law of Stokes for the rotation of a particle in a viscous medium. The purpose of the present research is to test the dipole theory by making measurements of the frequency variation of the dielectric constant for viscous solutions of various polar substances in nonpolar solvent media. To this end it was necessary to devise an accurate method of measurement for the dielectric constant of a liquid system at frequencies as high as 2×${10}^7$ cycles per second. The apparatus used is briefly described. The dielectric constants of rosin solutions in mineral oils of varying viscosity are tabulated and calculations for the inner-frictional constant for these systems are made. The effect of viscosity upon the behavior of mixtures of "floricin," paraffin oil and vaseline is also investigated. It is found to have little effect, a fact of considerable interest with regard to the inner structure of these solutions. An explanation for the failure to observe an expected dispersion in several experiments is attempted. The comparison of the experimental results with the requirements of the Debye theory leads to several interesting conclusions. There are objections to the use of the ordinary coefficient of viscosity of the medium to measure the frictional resistance to the rotation of a molecule when the discontinuities of the fluid are large compared with the size of the rotating particle and probably in other cases as well. Calculations from the experimental data make possible a differentiation between systems in which the suspended particles are all of one size or monodisperse, and in which they are polydisperse. Finally, there is suggested the type of experiment which must be made if a quantitative verification of the theory is sought.