Two discoveries have been made by scientists at Queen Mary University of London about the behavior of supercritical matter.
The picture of matter at high temperature and pressure was not understood because it was blurry. The supercritical matter was thought to become hot, dense and heterogeneous when it was above the critical point.
There was new physics yet to be discovered about this matter, according to the researchers.
They made two key discoveries by applying two parameters to the system. They discovered that there is a fixed point between the two where matter can change its physical properties. The supercritical matter is easy to understand and close to all systems studied.
Understanding supercritical matter has many practical applications, such as hydrogen and helium being supercritical in gas giant planets, and therefore governing their physical properties. Supercritical fluids have been shown to be very efficient at destroying hazardous waste, but engineers want guidance from theory in order to improve their efficiency.
The professor of physics at Queen Mary University of London said that the universality of the supercritical matter opens a way to a new physically transparent picture of matter. Understanding and predicting supercritical properties in green environmental applications, astronomy and other areas is an exciting prospect from the point of view of fundamental physics.
Upcoming developments are likely to be exciting on this journey. It invites the question of whether the fixed point is related to higher-order transitions. Is it necessary to use the existing ideas in the phase transition theory to describe it? New exciting questions can be identified as we push the boundaries of what is known.
There is a methodology.
Theories of gases, liquids and Solids were not applicable to understand supercritical matter. It was not clear what physical parameters would reveal the most important aspects of the supercritical state.
Researchers used two parameters to describe the supercritical matter.
This is the first thing. The first property is the heat capacity, which shows how efficiently the system absorbs heat and contains important information about the system's degrees of freedom.
There are two This is the length of waves that can travel in the system. The phase space is governed by this length. Something really interesting occurs when this length becomes equal to the interatomic separation.
The scientists found that the matter at extreme temperatures and pressures becomes universal.
It's two-fold. The plot of heat capacity vs wave propagation length has a fixed point that shows the transition between two different supercritical states. The supercritical matter's physical properties change when it crosses this point. Scientists have been thinking about how to separate the two states for a long time.
The location of this point is very close in all systems studied. All other transition points are different to this one. The critical point where the gas-liquid boiling line ends is different in different systems. The same point in all systems tells us that the supercritical matter is easy to understand.
The paper, "Double universality of the transition in the supercritical state", is the main result of the work.
More information: C. Cockrell et al, Double universality of the transition in the supercritical state, Science Advances (2022). DOI: 10.1126/sciadv.abq5183. www.science.org/doi/10.1126/sciadv.abq5183 Journal information: Science Advances
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