The editorial board of the journal Physical Chemistry Chemical Physics highly estimated a paper of Krasnoyarsk scientists published together with foreign colleagues fr om Belgium and Germany. The paper published at the beginning of this year, which considers the problems of multi-component mixing, became a «hot» one, with the highest number of citations.

The journal Physical Chemistry Chemical Physics publishes annually more than three thousand scientific papers concerning the problems of physical chemistry and chemical physics. This is a well-known international journal with the high citation index. Every year the editorial board chooses about two hundred of the most popular papers. This year, a study carried out by Krasnoyarsk scientists together with foreign colleagues was short-listed in this journal.
  
The «hot» research of the Russian and foreign scientists is devoted to the theoretical measurement of the diffusion coefficients of ternary mixtures obtained in the course of experiments at the International space station. The samples whose mixing was studied in space, were the mixtures of tetrahydronaphthalene-isobutyl benzene-dodecane, cyclohexane-toluene-methanol, water-ethanol-triethylene glycol. Every triplet of the components includes compounds typical for carbohydrate deposits, e.g., for oil.

The investigations of diffusion in ternary mixtures are carried out in space in order to get rid of the action of Earth’s gravitation. For scientists it is important to understand how mixing occurs under ideal conditions when the liquid is not influenced by gravitation. Ternary mixtures are prepared under laboratory conditions on the Earth. Then, they are sent to space wh ere their diffusion coefficients are measured. The obtained data are processed on the Earth.

In the «hot» paper for the first time the researchers analyzed the dependencies of the diffusion coefficients of the ternary mixtures on the frame of reference in which they can be presented. The process of mixing two components is described by a diffusion coefficient whose value does not depend on the reference frame. The problems in interpreting the results of measurements appear for mixtures with three or bigger number of components. During the analysis of one of the reference frames, negative values of the main diffusion coefficients were obtained for several compositions of the mixture. In this case, some components of this mixture must get separated rather than mixed.

«Theoretically, the negative main diffusion coefficients imply that upon mixing of three components two of them will mix but the third one will tend to get separated; i.e. the diffusion of a pair of the components causes the inverse diffusion of the third component. In literature there have been no measurements of negative main diffusion coefficients», explained one of  the co-authors of the paper, junior research associate of the Institute of Computational Modeling KSC SB RAS Sofja Kozlova.

The scientists raised a question concerning the physical basis of the negative main diffusion coefficients and analyzed the initial data in the «challenging» cases. As a result, they made the corrections of the experimental values of the cross diffusion coefficients within the calculation error. Of significance is that the measurement of the cross diffusion coefficients requires many efforts and accurate experimental equipment. There was inaccuracy in the obtained data, which influenced further calculations.

«Nobody expected that our research would raise many questions concerning the experimental procedure itself. There is a large research team from many countries and the experiments are carried out in the International Space Station. Thanks to the joint efforts we were able to reveal the challenging issues of the experiment», emphasized Sofja Kozlova.

The results of transformations of the diffusion coefficients for ternary mixtures can be compared with the conclusions obtained by other research groups on the basis of the alternative methods of measurements. They can be used for testing and refining the models of mixtures based on the currently spread method of molecular dynamics. The investigation results of the behavior of multi-component mixtures are important in such industrial areas as fuel power production, extraction of commercial minerals, and cooling systems. In general, they are necessary for calculating the processes of convection, thermal diffusion, or any phenomena of heat and mass transfer.