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 percentage of HDL exists while below the critical pressure a higher percentage of LDL is present. The ratio r = LDL/(LDL + HDL) 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 at the associated liquid-liquid critical point, the ratio of LDL to HDL is exactly one.

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 papers having been published, though only a few of these investigations have been experimental[4][5][6][7][8] 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: 324–328. Bibcode:1992Natur.360..324P. doi:10.1038/360324a0.
  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: 104502. arXiv:1312.4871. Bibcode:2014JChPh.140b4502M. doi:10.1063/1.4867287.
  4. ↑ Mishima, O.; Stanley, H. E. (1998). "Decompression-Induced Melting of Ice IV and the Liquid-Liquid Transition in Water". Nature. 392: 164–168. Bibcode:1998Natur.392..164M. doi:10.1038/32386.
  5. ↑ Vasisht, V. V.; Saw, S.; Sastry, S. (2011). "Liquid-Liquid Critical Point in Supercooled Silicon". Nat. Phys. 7: 549–555. arXiv:1103.3473. Bibcode:2011NatPh...7..549V. doi:10.1038/nphys1993.
  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: 170–173. Bibcode:2000Natur.403..170K. doi:10.1038/35003143.
  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: 125503. Bibcode:2013PhRvL.110l5503C. doi:10.1103/PhysRevLett.110.125503. PMID 25166820.
  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: 20618–20622. arXiv:1501.02380. doi:10.1021/acs.jpcc.5b07635.
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