A liquid–liquid critical point (or LLCP) is the endpoint of a liquid–liquid phase transition line (LLPT); it is a critical point where two types of local structures coexist at the exact ratio of unity. This hypothesis was first developed by Peter Poole, Francesco Sciortino, Uli Essmann and

H. Eugene Stanley Harry Eugene Stanley (born March 28, 1941) is an American physicist and University Professor at Boston University. He has made seminal contributions to statistical physics and is one of the pioneers of interdisciplinary science. His current r ...

Boston Boston (), officially the City of Boston, is the state capital and most populous city of the Commonwealth of Massachusetts, as well as the cultural and financial center of the New England region of the United States. It is the 24th- mo ...

to obtain a quantitative understanding of the huge number of anomalies present in water. Near a liquid–liquid critical point, there is always a competition between two alternative local structures. For instance, in supercooled water, two types of local structures have been predicted: a low-density local configuration (LD) and a high-density local configuration (HD), so above the critical pressure, the liquid is composed by a majority of HD local structure, while below the critical pressure a higher fraction of LD local configurations is present. The ratio between HD and LD configurations is determined according to the thermodynamic equilibrium of the system, which is often governed by external variables such as pressure and temperature. The liquid–liquid critical point theory can be applied to several liquids that possess the

tetrahedral In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the ...

symmetry. The study of liquid–liquid critical points is an active research area with hundreds of articles having been published, though only a few of these investigations have been experimental since most modern probing techniques are not fast and/or sensitive enough to study them.

References

{{DEFAULTSORT:Liquid-liquid critical point Critical phenomena Phase transitions Ice