Crossover between liquid-like and gas-like behaviour in CH₄ at 400 K

Smith, D.; Hakeem, M. A.; Parisiades, P.; Maynard-Casely, H. E.; Foster, D.; Eden, D.; Bull, D. J.; Marshall, A. R.L.; Adawi, A. M.; Howie, R.; Sapelkin, A.; Brazhkin, V. V.; Proctor, J. E.

Abstract

We report experimental evidence for a crossover between a liquid-like state and a gas-like state in fluid methane (CH₄). This crossover is observed in all of our experiments, up to 397 K temperature; 2.1 times the critical temperature of methane. The crossover has been characterized with both Raman spectroscopy and X-ray diffraction in a number of separate experiments, and confirmed to be reversible. We associate this crossover with the Frenkel line - a recently hypothesized crossover in dynamic properties of fluids extending to arbitrarily high pressure and temperature, dividing the phase diagram into separate regions where the fluid possesses liquid-like and gas-like properties. On the liquid-like side the Raman-active vibration increases in frequency linearly as pressure is increased, as expected due to the repulsive interaction between adjacent molecules. On the gas-like side this competes with the attractive Van der Waals potential leading the vibration frequency to decrease as pressure is increased.

Citation

Smith, D., Hakeem, M. A., Parisiades, P., Maynard-Casely, H. E., Foster, D., Eden, D., …Proctor, J. E. (2017). Crossover between liquid-like and gas-like behaviour in CH₄ at 400 K. Physical Review E, 96(5), Article 052113. https://doi.org/10.1103/PhysRevE.96.052113

• Journal Article Type: Article
• Acceptance Date: Oct 13, 2017
• Online Publication Date: Nov 9, 2017
• Publication Date: Nov 9, 2017
• Deposit Date: Oct 23, 2017
• Publicly Available Date: Nov 9, 2017
• Journal: Physical review. E, Statistical, nonlinear, and soft matter physics
• Print ISSN: 2470-0045
• Electronic ISSN: 2470-0053
• Publisher: American Physical Society
• Peer Reviewed: Peer Reviewed
• Volume: 96
• Issue: 5
• Article Number: 052113
• DOI: https://doi.org/10.1103/PhysRevE.96.052113
• Public URL: https://hull-repository.worktribe.com/output/455876
• Publisher URL: https://journals.aps.org/pre/abstract/10.1103/PhysRevE.96.052113
• Additional Information: This is a description of an article accepted for future publication in Physical review. E, Statistical, nonlinear, and soft matter physics