About five years ago, we took up the analysis of the weak interaction between the same or different kinds of molecules in a liquid state by comparing results of the measurement of dielectric constant with these of the measurements of refractive index and viscosity. The measurement of dielectric constant has often been used for the estimation of mplecular structure, but its application to the estimation of mutual interaction has not practically been undertaken so far as this method is highly sensitive. Owing to the remarkable character of the method, it seems very useful for the estimation of very weak interaction between the molecules in mixed solvents. From these standpoints, we have examined the weak interaction between the dioxane and benzene molecules with reference to the viscosity analysis.
The dielectric constant vs. composition curves clearly showed the same inflextion points at the equi-molar composition and the same results were also obtained in the viscosity vs. composition curves for the mixture of dioxane and benzene. These results show that the dioxane molecule and the benzene molecule combine to form a weak intermediate complex in the above mixture of equi-molar composition.
This paper deals with the nature of the above mentioned molecular interaction from the viw-point of the internal friction of the solvent mixture in Newton flow and have intended to deduce a theoretical equation which describes the relation between the viscosity and the composition. The experimental certifications of the above equation were undertaken by the use of dioxane-benzene and dioxane-cyclohexane systems.
The basic idea on deducing the above equation was that the internal friction should be resulted from the force of molecular interaction which is effective only in a limited space around the center of the considering molecules. Naturally, the substance of this force may perphaps be started from the dipole-dipole or atom-dipole interaction as Debye mentioned. Accordingly, so far as taking these assumptions, the idea on the nature of viscosity must be essentially introduced from the problem of the probability of penetration of the considering molecules into such space as above mentioned, and it must be described only by the number of molecules when the temperature of the system and the other conditions were fixed.