Neutron studies of diffusion processes near a singular point in a dilute aqueous solution of ethanol

Abstract

The problem considered in this work relates to the physics of liquids. Rather, to the physics of dynamic processes in liquids. The method of quasielastic scattering of slow neutrons was used to study the dynamics of molecules of the water-ethanol system as a function of concentration at a temperature of 8 °C and as a function of temperature at a concentration of X = 0.04 molar particles (mol. particl.). The overall coefficient of self-diffusion of molecules D, its single-particle Ds-p and collective Dcoll components, as well as the time of settled life of a molecule in a vibrational state t, are determined. The region of small concentrations was studied in detail, where in the vicinity of concentrations X = 0.04 mol. particl. and X = 0.2 mol. particl. two minima are found in the coefficients D and Ds-p. Time t at these concentrations increases significantly. This indicates a significant decrease in the intensity of the activation mechanism of molecular diffusion at these concentrations, which is quite possibly caused by the binding of water and ethanol molecules into complexes (clusters). Similarly, a deep minimum was found in the D and Ds-p coefficients near the temperature of 4 °С. Time t at this temperature also increases. That is, at a temperature of 4 °C, the intensity of the activation mechanism of the diffusion of solution molecules decreases. Therefore, at a concentration of X = 0.04 mol. particl. and at a temperature of 4°C, a special point exists in the water-ethanol system. However, its position does not coincide with the data on scattering light.