The Dielectric Properties of Binary Systems of Ketones and Hydrocarbons

Abstract

Experimental work on the dielectric properties of solid systems of long-chain polar and non-polar compounds has been performed by Jackson(l), Sillars(2), and Pelmore(3) with dilute solutions of esters in paraffin wax. In subsequent theoretical studies in this field Fröhlich(4) adopted, as a model, a crystalline long-chain paraffin in which a small proportion of the molecules were assumed to be replaced by long-chain polar molecules. Taking Debye's theory of dielectric absorption in polar solids as a basis, this led to the derivation of a relationship between the relaxation time and the number of links in the polar molecule. In order to obtain experimental results more closely related to the theory, electrical measurements have now been made with symmetrical long-chain ketones in pure crystalline hydrocarbon solvents. The variation of dielectric constant and loss angle with frequency for these systems is found to be approximately in agreement with the Debye theory of dielectric absorption. For ketones of chain-length shorter than that of the hydrocarbon solvent the relationship between relaxation time and chain-length is of the type expected from Fröhlich's theory, but displaced towards lower frequencies. The results show that, in applying the theoretical relationship to systems of long-chain polar and non-polar compounds, it would be necessary to determine new constants for each different type of polar compound and for each different solvent. The results of electrical measurements of ketone-hydrocarbon systems with ketones of varying chain-length (both less and greater than that of the solvent) are in accordance with conclusions from previous X-ray studies of long-chain hydrocarbons. The effects of dipole interaction on the dielectric absorption of systems of laurone and n-hexacosane, are discussed in relation to the solid-liquid phase diagram. The results of dielectric measurements with pure crystalline compounds suggest that dipole interaction and electrical cooperative effects are larger in ketones than in esters of similar chain-length.