The Anomalous Behavior of Thermodynamic Parameters in the Three Widom Deltas of Carbon Dioxide-Ethanol Mixture

Using molecular dynamics, we demonstrated that in the mixture of carbon dioxide and ethanol (25% molar fraction) there are three pronounced regions on the p-T diagram characterized by not only high-density fluctuations but also anomalous behavior of thermodynamic parameters. The regions are interpreted as Widom deltas. The regions were identified as a result of analyzing the dependences of density, density fluctuations, isobaric thermal conductivity, and clustering of a mixture of carbon dioxide and ethanol in a wide range of pressures and temperatures. Two of the regions correspond to the Widom delta for pure supercritical carbon dioxide and ethanol, while the third region is in the immediate vicinity of the critical point of the binary mixture. The origin of these Widom deltas is a result of the large mixed linear clusters formation.

Automated summary

Using molecular dynamics simulation, three Widom δ regions were identified in the p-T diagram of a mixture of carbon dioxide and ethanol, characterized by high-density fluctuations and anomalous behavior of thermodynamic parameters. These regions are attributed to the formation of large mixed linear clusters, with two corresponding to pure supercritical carbon dioxide and ethanol, and the third located near the critical point of the binary mixture.