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

Smith, D; Hakeem, M; Parisiades, P; Maynard-Casely, HE; Foster, D; Eden, D; Bull, DJ; Marshall, ARL; Adawi, AM; Howie, R; Sapelkin, A; Brazhkin, VV; Proctor, JE

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 Waal’s potential leading the vibration frequency to decrease as pressure is increased.

• Journal Article Type: Article
• Acceptance Date: Oct 12, 2017
• Publication Date: Nov 9, 2017
• Deposit Date: Oct 23, 2017
• Publicly Available Date: Nov 20, 2017
• Journal: Physical Review E (PRE)
• Print ISSN: 2470-0045
• Electronic ISSN: 2470-0053
• Publisher: American Physical Society
• Volume: 96
• Issue: 5
• Pages: 052113
• DOI: https://doi.org/10.1103/PhysRevE.96.052113
• Publisher URL: http://dx.doi.org/10.1103/PhysRevE.96.052113
• Related Public URLs: https://journals.aps.org/pre/