Dielectric Properties of the Hydrogen-bonded Liquids. Steric Effects on Dielectric Properties in Glycerol and Acetylated Glycerols

Abstract

Abstract The dielectric constant and the dielectric loss of a monohydroxy molecule (glycerol diacetate) and a dihydroxy molecule (glycerol monoacetate) in the pure liquid state were measured over the frequency range from 23 Hz to 3 MHz in order to elucidate the relation between the steric effects of the acetoxyl group and the dielectric properties of alcohols. For a better understanding, the results of this work were discussed together with those of glycerol and glycerol triacetate. The static dielectric constants decrease in the order of glycerol, glycerol monoacetate, glycerol diacetate, and glycerol triacetate. This order agrees with the order of the decreasing number of hydroxyl groups per molecule. On the other hand, the four curves of a temperature variation of the relaxation times almost form one curve, although the molecular weights and interaction, which are important factors for the determination of relaxation times, differ greatly among the four molecules. Accordingly, it is concluded that the decrease in molecular weight due to the replacement of the acetyl group CH3CO by a hydrogen atom counteracts the enhanced molecular interaction due to the increased OH···O hydrogen bonds. The experimental Cole-Cole arcs of the complex dielectric constants were well represented by the calculated curve of the Davidson-Cole empirical equation, for glycerol mono- and diacetate as well as for glycerol.