Widom line
In the context of supercritical fluids, the Widom line is the line emanating from the critical point which represents the maxima or minima in certain physical properties of a fluid substance, such as the speed of sound, isothermal compressibility, isochoric and isobaric heat capacities. A common criterion for locating the Widom line is indeed the maximum in the isobaric heat capacity.
More generally, the Widom line is the line in the phase diagram of a fluid substance along which the correlation length has its maximum.[1] It always emanates from a critical point and has been also discussed for example in the context of the hypothesized liquid–liquid critical point (or second critical point) of water.[2]
Other proposed similar boundary lines include for example the Fisher-Widom line and the Frenkel line.
Overview[edit]
The Widom line has been suggested[3] to separate liquid-like behaviour and gas-like behaviour in supercritical fluids, where traditional phase boundaries between liquid and gas no longer exist. Specifically, the supercritical fluid has gas-like behavior on the low-pressure side of the Widom line and liquid-like behavior on the high-pressure side of the Widom line. This separation is a continuous crossover in some properties of the fluid and has been observed experimentally on various molecular systems[4].
The concept of the Widom line provides a useful framework for characterizing and predicting the properties of fluids, which are important for scientific research as well as various industrial processes. Such a concept is relevant to the physical properties of any single-component fluid at sufficiently high pressures and temperatures, and its study is an active and ongoing research area.
The Widom line is named after the theoretical physicist Benjamin Widom.
See also[edit]
References[edit]
- ^ H. E. Stanley, P. Kumar, G. Franzese, L. Xu, Z. Yan, M. G. Mazza, S. V. Buldyrev, S.-H. Chen and F. Mallamace "Liquid polyamorphism: Possible relation to the anomalous behaviour of water", European Physical Journal - Special Topics 161 pp. 1-17 (2008)
- ^ Limei Xu, Pradeep Kumar, S. V. Buldyrev, S.-H. Chen, P. H. Poole, F. Sciortino, and H. E. Stanley "Relation between the Widom line and the dynamic crossover in systems with a liquid–liquid phase transition", PNAS 102 pp. 16558-16562 (2005)
- ^ Simeoni, Giovanna Giulia; Bryk, Taras; Gorelli, Federico Aiace; Krisch, Michael; Ruocco, Giancarlo; Santoro, Mario; Scopigno, Tullio (2010). "The Widom line as the crossover between liquid-like and gas-like behaviour in supercritical fluids". Nature Physics. 6 (7): 503–507. doi:10.1038/nphys1683. ISSN 1745-2473.
- ^ U. Ranieri, F. Formisano, F. A. Gorelli, M. Santoro, M. M. Koza, A. De Francesco, L. E. Bove "Crossover from gas-like to liquid-like molecular diffusion in a simple supercritical fluid", Nature Communications 15, 4142 (2024)