{"id":1970,"date":"2022-01-05T12:46:45","date_gmt":"2022-01-05T12:46:45","guid":{"rendered":"https:\/\/hub.salford.ac.uk\/sirc-materials-and-physics\/?page_id=1970"},"modified":"2022-01-05T12:46:46","modified_gmt":"2022-01-05T12:46:46","slug":"liquids-and-supercritical-fluids","status":"publish","type":"page","link":"https:\/\/hub.salford.ac.uk\/sirc-materials-and-physics\/liquids-and-supercritical-fluids\/","title":{"rendered":"Liquids and Supercritical Fluids"},"content":{"rendered":"\n

The picture in the standard undergraduate textbook of the basic phases of matter on the pressure-temperature phase diagram is a relatively simple one (shown below).\u00a0 From the triple point onwards, the liquid state is separated from the solid state by the melting line and from the gas state by the boiling \/ vapour pressure line.\u00a0 This latter curve ends at the critical point, beyond which there is no transition between liquid and gas states; matter in this region of the phase diagram is in some halfway house between liquid and gas, known as the supercritical fluid state<\/a>.<\/p>\n\n\n\n

\"\"
The basic states of matter on the pressure-temperature phase diagram<\/figcaption><\/figure>\n\n\n\n

However, this simple model raises a number of questions.\u00a0 In the liquid fluid close to the melting line the sample has more in common with a solid than with a gas, in terms of density, heat capacity and viscosity for instance.\u00a0 So how does the fluid transition from the gas state, to a state with properties that have much in common with solids, when a path is followed going above the critical point so not encountering the boiling line (or any other first order phase transition)?\u00a0 Furthermore, the liquid state close to the melting line has characteristics that seem very similar to the supercritical fluid state close to the melting line, so is the critical temperature still a meaningful parameter at pressure \/ density significantly higher than the critical point?<\/p>\n\n\n\n

It has been possible to study dense fluids with techniques such as X-ray and neutron diffraction, and Raman spectroscopy, and perform molecular dynamics simulations on these systems, for decades yet it is only recently (since 2012<\/a>) that physicists have started to get at the answers to the questions above.\u00a0 Here at Salford we have been at the forefront of this research, producing key publications in Phys. Rev. E (2017)<\/a> and J. Phys. Chem. Lett. (2019)<\/a> and the first textbook<\/a> to cover these recent advances.<\/p>\n\n\n\n

\"\"
University of Salford Ph.D. student Dean Smith inserting a diamond anvil high pressure cell onto the I15 extreme conditions beamline at the Diamond Light Source.<\/figcaption><\/figure>\n\n\n\n

Experimentally we have conducted studies of dense liquids and supercritical fluids using our own facilities as well as at central facilities such as the Diamond Light Source<\/a>, European Synchrotron Radiation Facility<\/a> and ISIS Pulsed Neutron Source<\/a>.\u00a0 Computationally we have performed molecular dynamics simulations at our own computing facilities, as well as developing our own code in C++<\/a> to test out the degree to which theoretical models based on resemblance to the solid state can explain the trends in heat capacity observed in dense liquids and supercritical fluids.<\/p>\n\n\n\n

The modern picture of the liquid and supercritical fluid states is something like the diagram below, in which the liquid state is divided into regions exhibiting gas-like properties (non-rigid liquid), and properties reminiscent of a dense, rigid, liquid.\u00a0 The liquids we are familiar with in everyday life are generally rigid liquids.<\/p>\n\n\n\n

\"\"
Schematic diagram showing the modern understanding of the basic states of matter on the pressure-temperature phase diagram.<\/figcaption><\/figure>\n\n\n\n

Unlike the non-rigid liquid, the rigid liquid can exist above the critical point up to arbitrarily high temperature if sufficient pressure is applied.\u00a0 The dividing line between these states (the Frenkel line, named after the Russian physicist Yakov Ilyich Frenkel<\/a>) is not a discontinuous phase transition similar to melting or boiling lines, rather a narrow (but finite) region in which properties change from gaslike to liquidlike.<\/p>\n\n\n\n

Having said that, the picture is constantly evolving.\u00a0 Very recently colleagues at the University of Edinburgh have used our neutron scattering data on fluid nitrogen to train their molecular dynamics simulations on this fluid, resulting in the prediction that the Frenkel line (instead of beginning somewhere on the boiling line) begins at the triple point<\/a>.<\/p>\n\n\n\n

Why is all this important?\u00a0 Well, supercritical fluids do have a range of industrial applications (reviewed in our recent book), but the main direct application of this work is in planetary science.\u00a0 Gas giant planets and many of their moons consist of complex fluid mixtures held under high pressure-temperature conditions at which the Frenkel line is likely to be encountered.\u00a0 Work to understand the consequences of the Frenkel line for the properties of fluid mixtures is currently at a very early stage. Our research on liquids and supercritical fluids continues, and postgraduate students have played a key role in this work over the years.\u00a0 If you are interested in applying, you can return to the homepage<\/a> and read more on the postgraduate study menu, or start your application here<\/a>.<\/p>\n\n\n\n

<\/p>\n\n\n\n

Our recent publications on liquids and supercritical fluids<\/strong><\/p>\n\n\n\n

Structural Markers of the Frenkel Line in the Proximity of Widom Lines<\/strong><\/p>\n\n\n\n

C.G. Pruteanu, J.E. Proctor, O. Alderman and J.S. Loveday, J. Phys. Chem. B 125<\/strong>, 8902 (2021). Link<\/a><\/em><\/p>\n\n\n\n

The liquid and supercritical fluid states of matter<\/strong><\/p>\n\n\n\n

JE Proctor, CRC Press (2020). Link<\/a><\/em><\/p>\n\n\n\n

Modelling of liquid internal energy and heat capacity over a wide pressure-temperature range from first principles<\/strong><\/p>\n\n\n\n

J.E. Proctor, Phys. Fluids 32<\/strong>, 107105 (2020). Link<\/a><\/em><\/p>\n\n\n\n

On the Transition from Gas-like to Liquid-like Behaviour in Supercritical N2<\/sub><\/strong><\/p>\n\n\n\n

J.E. Proctor. C.G. Pruteanu, I. Morrison, I.F. Crowe and J.S. Loveday, J. Phys. Chem. Lett. 10<\/strong>, 6584 (2019). Link<\/a><\/em><\/p>\n\n\n\n

Liquid Mysteries <\/strong>Physics World magazine, May 2018.  https:\/\/physicsworld.com\/a\/liquid-mysteries\/<\/a><\/p>\n\n\n\n

Observation of liquid-liquid phase transitions in ethane at 300 K<\/strong><\/p>\n\n\n\n

J.E. Proctor, M. Bailey, I. Morrison, M.A. Hakeem and I.F. Crowe, J. Phys. Chem. B 122<\/strong>, 10172 (2018). Link<\/a><\/em><\/p>\n\n\n\n

Dynamics, thermodynamics and structure of liquids and supercritical fluids: crossover at the Frenkel line<\/strong><\/p>\n\n\n\n

Yu.D. Fomin, V.N. Ryzhov, E.N. Tsiok, J.E. Proctor, C. Prescher, V.B. Prakapenka, K. Trachenko and V.V. Brazhkin, J. Phys.: Cond. Mat. 30<\/strong>, 134003 (2018). Link<\/a><\/em><\/p>\n\n\n\n

Crossover between liquidlike and gaslike behaviour in CH4<\/sub> at 400 K<\/strong><\/p>\n\n\n\n

D. Smith, M.A. Hakeem, P. Parisiades, H.E. Maynard-Casely, D. Foster, D. Eden, D.J. Bull, A.R.L. Marshall, A.M. Adawi, R. Howie, A. Sapelkin, V.V. Brazhkin and J.E. Proctor, Phys. Rev. E 96<\/strong>, 052113 (2017). Link<\/a><\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

The picture in the standard undergraduate textbook of the basic phases of matter on the pressure-temperature phase diagram is a relatively simple one (shown below).\u00a0 From the triple point onwards, the liquid state is separated from the solid state by the melting line and from the gas state by the boiling \/ vapour pressure line.\u00a0 […]<\/p>\n","protected":false},"author":240,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"footnotes":""},"class_list":["post-1970","page","type-page","status-publish","hentry"],"acf":[],"yoast_head":"\nLiquids and Supercritical Fluids | Materials and Physics | University of Salford<\/title>\n<meta name=\"description\" content=\"Read about our groundbreaking research into the nature of liquids and supercritical fluids\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link 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