The static dielectric constant of pentanol diluted in decane, cyclohexane and carbon tetrachloride was measured as a function of temperature, at different concentrations. The experimental points were adjusted using the Onsager equation to which a term reducing the molecular interaction was added. Such an empirical equation has already been published for decane solutions. Good agreement between experimental and fitted values of the permittivity was found. The results obtained for the different solvents used are compared and analysed, together with the parameters resulting from the fittings.
IntroductionIn a previous report [ 11, the permittivity behaviour of decane-pentanol mixtures was analysed as a function of temperature at different concentrations. The results were fitted to an empirically modified Onsager equation for mixtures [24]. This modification emphasizes the dependence of permittivity on temperature. The equations for diluted polar liquids do not include the following effects. (a) The molecules are not spherical (this condition is assumed by Onsager in the deduction of his expression) [4], and (b) the rotations of the dipoles in the medium are hindered (this effect is included in Kirkwood's g [5], but only for pure polar liquids). As the factor g has no exact method of calculation and there are no models of structures for diluted alcohols, the empirical modification of the Onsager expression assumes explicit temperature dependence and a solvent dependent parameter. It is also assumed that there is no correction for 20 "C, the reference temperature, and differences in behaviour appear for other temperatures.For the present work, two solvents were selected (cyclohexane and carbon tetrachloride) in order to compare the results obtained for the same alcohol with solvent molecules of different shapes. Since decane is stick-shaped, cyclohexane is like a disc and carbon tetrachloride is sphere-like, the effects on the dipoledipole interaction should be different.
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