Ternary liquid diffusion coefficients near plait points

Do ternary liquid mixtures exhibit negative main Fick diffusion coefficients?

“…The mixture cyclohexane -toluene -methanol exhibits liquid-liquid phase seperation. In particular for this mixture type, having a plait point, there are ongoing discussions in the literature about the existence of negative main diffusion coefficients [5,19,23]. Our experience in measuring diffusion coefficients of liquids with a demixing zone [37] showed that the experiments are very delicate and require maintaining the specified temperature not only in the cell, but also throughout all cabling, tubes, syringes and interferometer.…”

“…From a mathematical point of view, the transformation of diffusion matrices is reciprocal and provides equal matrix eigenvalues for all three reference frames. We are not aware of publications in which negative main diffusion coefficients were measured experimentally, except for several discrete measurements near the plait point [18,19]. Instead, they were obtained as a result of computations, e.g., due to solvent change [5,23].…”

“…Kirkaldy and Purdy [18] as well as Clark and Rowley [19] argued that very non-ideal solutions, near their plait point, may exhibit negative main Fick diffusion coefficients. However, the majority of experimental results, also those for mixtures with liquid-liquid phase separation [7,8], suggest the general validity of requirement (4) [20,21].…”

Form of multicomponent Fickian diffusion coefficients matrix

“…Examination of the reported D shows that in ternary mixtures, nine data points from two mixtures are reported with negative diagonal D V elements: (water + 2-propanol + cyclohexane 2 ) [32]; and, (acetic acid + chloroform + water) [38,39]. Mixture conditions and D V ij are shown in tables 6 and 7.…”

“…Volume-based diffusion coefficients, D V ij  10 9 m 2 Á s À1 , as functions of temperature T for water(1), 2-propanol(2), and cyclohexane b mixture at p = 0.1 MPa [32]. …”