Liquid–liquid critical point

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 H. Eugene Stanley[1] to obtain a quantitative understanding of the huge number of anomalies present in water.[2]

Near a liquid–liquid critical point, there is always a mixture of two alternative local structures. For instance, in supercooled water, two types of local structures exist: a low-density liquid (LDL) and a high-density liquid (HDL), so above the critical pressure, a higher fraction of HDL exists, while below the critical pressure a higher fraction of LDL is present. The ratio r = LDL / (LDL + HDL) of phase amounts is determined according to the thermodynamic equilibrium of the system, which is often governed by external variables such as pressure and temperature.[3] A discontinuity is present in r when crossing the liquid–liquid phase transition, which separates the LDL-rich phase from the LDL-poor phase. At any point of the liquid–liquid phase transition, including the associated liquid–liquid critical point, the ratio of LDL to HDL is exactly one (r = 1/2).

The liquid–liquid critical point theory can be applied to all liquids that possess the tetrahedral 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[4][5][6][7][8][9] since most modern probing techniques are not fast and/or sensitive enough to study them.

References
  1. Poole, P. H.; Sciortino, F.; Essmann, U.; Stanley, H. E. (1992). "Phase Behavior of Metastable Water". Nature. 360 (6402): 324–328. Bibcode:1992Natur.360..324P. doi:10.1038/360324a0.CS1 maint: uses authors parameter (link)
  2. "Anomalous properties of water". Retrieved 30 August 2015.
  3. Holten, V.; Palmer, J. C.; Poole, P. H.; Debenedetti, P. G.; Anisimov, M. A. (2014). "Two-state thermodynamics of the ST2 model for supercooled water". J. Chem. Phys. 140 (10): 104502. arXiv:1312.4871. Bibcode:2014JChPh.140b4502M. doi:10.1063/1.4867287. PMID 24628177.CS1 maint: uses authors parameter (link)
  4. Mishima, O.; Stanley, H. E. (1998). "Decompression-Induced Melting of Ice IV and the Liquid–Liquid Transition in Water". Nature. 392 (6672): 164–168. Bibcode:1998Natur.392..164M. doi:10.1038/32386.CS1 maint: uses authors parameter (link)
  5. Vasisht, V. V.; Saw, S.; Sastry, S. (2011). "Liquid–Liquid Critical Point in Supercooled Silicon". Nat. Phys. 7 (7): 549–555. arXiv:1103.3473. Bibcode:2011NatPh...7..549V. doi:10.1038/nphys1993.CS1 maint: uses authors parameter (link)
  6. Katayama, Y.; Mizutani, T.; Utsumi, W.; Shimomura, O.; Yamakata, M.; Funakoshi, K. (2000). "A First-Order Liquid–Liquid Phase Transition in Phosphorus". Nature. 403 (6766): 170–173. Bibcode:2000Natur.403..170K. doi:10.1038/35003143. PMID 10646596.CS1 maint: uses authors parameter (link)
  7. Cadien, A.; Hu, Q. Y.; Meng, Y.; Cheng, Y. Q.; Chen, M. W.; Shu, J. F.; Mao, H. K.; Sheng, H. W. (2013). "First-Order Liquid–Liquid Phase Transition in Cerium". Phys. Rev. Lett. 110 (12): 125503. Bibcode:2013PhRvL.110l5503C. doi:10.1103/PhysRevLett.110.125503. PMID 25166820.CS1 maint: uses authors parameter (link)
  8. Yen, F.; Chi, Z. H.; Berlie, A.; Liu, X. D.; Goncharov, A. F. (2015). "Dielectric Anomalies in Crystalline Ice: Indirect Evidence of the Existence of a Liquid−Liquid Critical Point in H2O". J. Phys. Chem. C. 119 (35): 20618–20622. arXiv:1501.02380. doi:10.1021/acs.jpcc.5b07635.CS1 maint: uses authors parameter (link)
  9. Gomes, Gabriel O.; Stanley, H. Eugene; Souza, Mariano de (2019-08-19). "Enhanced Grüneisen Parameter in Supercooled Water". Scientific Reports. 9 (1): 1–8. doi:10.1038/s41598-019-48353-4. ISSN 2045-2322.
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