Isotopic tracer self-diffusion. A method of studying the structure of liquid solutions

Abstract

The self-diffusion for both components in binary solutions: benzene-toluene (1), benzene-nitrobenzene (2), benzene-aniline (3), benzene-hexane (4) and benzene-cyclohexane (5) has been carried out. In Fig. 1a the benzene self-diffusion coefficients D B in the aforegoing solutions as a function of benzene mole fraction X B are presented. In Fig. 1b the self-diffusion coefficients of the others are presented. ▪ In order to describe these solutions it is proposed a new function called the excess self-diffusion coefficient D 4 i defined as: D E i = D i − (D o ix i + D o jx j) where D i denotes experimentally obtained self-diffusion coefficient for the given mole fraction x i and D o i, D o j are self-diffusion coefficients of pure components i and j respectively. The values of the excess self-diffusion coefficients for benzene D E B are presented in Fig. 2a and for other components in Fig. 2b. The studied solutions can be thus divided in three categories: i) D E i = 0, D E j = 0, the solutions are ideal e.g. benzene-toluene; ii) D E i < 0, D E j < 0, the solutions exhibiting specific interactions between molecules of both components leading to the formation of a common structure e.g. benzene-nitrobenzene and benzene-aniline; iii) D E i < 0, D E j < 0 the solutions without a common structure due to stronger interactions between i-i and j-j than i-j molecules. It seems that the new function introduced here i.e. the excess self-diffusion coefficient may be conveniently used to characterize the solutions investigated as it enables to determine explicitly the variation in mutual relations between molecules of all the components in solutions in respect to the interactions in pure liquids.