Solid, liquid, vapour - Where do you draw the line? [day-time seminar]
For most of the 20th century the common theoretical approach to understanding the liquid state was to treat liquids and supercritical fluids as dense non-ideal gases, justified on the basis that liquids and supercritical fluids share important properties with gases such as a lack of long-range order. But this approach has some shortcomings including that the densities of liquids under ambient conditions are generally close to those of solids, both orders of magnitude larger than for gases.
Therefore, the opposite theoretical approach has also been utilized – treating liquids using similar methods to solids. The solid-like approach was put forward by Frenkel in 1946 in Kinetic Theory of Liquids but it is only in the past 10 years that the power of this alternative approach has been truly appreciated. This has allowed accurate prediction of the heat capacities of liquids, and also the prediction that beyond the critical point there exists a narrow transition between liquid-like and gas-like states, christened the Frenkel line. This line, if its existence is proven, necessitates the revision of textbooks as well as providing knowledge with potential applications for the use of supercritical fluids in industry. Significantly, it is expected that the pressure-temperature path through the outer layers of the gas giant planets and some of their moons may pass right through this region of the phase diagram.
The Frenkel line should also be considered in the context of other changes in our understanding of the supercritical fluid state. Whilst the Frenkel line is unique in extending to arbitrarily high pressure and temperature, it is now accepted that there are a whole host of other dividing lines extending a finite distance from the critical point: Widom line(s), Joule Thomson curve, Amagat curve, Boyle curve… The supercritical region of the phase diagram is now known to be extremely complex, rather than a single homogeneous state. But to what extent do all these dividing lines actually mark real transitions? Hence the title of the seminar – where do you draw the line?
In this seminar the theoretical aspects of the kinetic theory of liquids will be reviewed and then the experimental evidence for the existence of the Frenkel line, produced very recently in my own work and the work of other researchers, will be presented. Some of the custom-constructed diamond anvil high pressure cells used for this research over the years will be shown – and we will see that diamonds are not forever!
About the Speaker
Dr John Proctor received his Ph.D. on “High pressure Raman spectroscopy of single-walled carbon nanotubes” from the University of Manchester in 2008. Since then he has spent his entire research career in the field of high pressure, principally utilizing the diamond anvil high pressure cell. He spent 4 years working as a postdoctoral researcher at the Centre for Science at Extreme Conditions at the University of Edinburgh before moving to the University of Hull followed by the University of Salford, where he is a senior lecturer in Physics and head of the Materials and Physics research group. He recently published his first textbook, “An Introduction to Graphene and Carbon Nanotubes” and has written for Physics World and The Conversation.
How to Book
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