Liquid–liquid_critical_point

# Liquid–liquid critical point A **liquid–liquid critical point** is the end point of a line of [[Phase_transition|phase transitions]] between two liquid forms of the same pure substance. Below the critical temperature the substance can exist as two distinct liquids, one less dense and one more dense, separated by a first-order transition. At the critical point the difference between them vanishes, just as the difference between liquid and vapor vanishes at an ordinary liquid–gas [[Critical_point_(thermodynamics)|critical point]]. Above it, the liquid changes smoothly from one local structure to the other. The best-known case is [[Water|water]]. In 1992 Peter Poole, Francesco Sciortino, Ulrich Essmann and H. Eugene Stanley used [[Molecular_dynamics|molecular dynamics]] simulations to propose that many of the [[Properties_of_water|anomalies of water]] come from a previously unknown critical point in deeply supercooled liquid water. In their picture, the low-density and high-density forms of amorphous ice have liquid counterparts, and these become indistinguishable above a critical point.[^poole1992] The low-density liquid has an open, tetrahedral network of [[Hydrogen_bond|hydrogen bonds]]; the high-density liquid is collapsed and packed more tightly. The hypothesis was hard to test because the predicted critical point lies in a range of temperature and pressure where supercooled water normally freezes within microseconds.[^kim2020] Simulations built up the case first. In 2020 Pablo Debenedetti, Sciortino and Gül Zerze found a liquid–liquid critical point in two realistic water models, at 172 ± 1 K and 1,861 ± 9 bar for TIP4P/2005 and at 188 ± 1 K and 1,739 ± 6 bar for TIP4P/Ice. They cautioned that such models cannot fix the location in real water.[^debenedetti2020] In 2025 Sciortino, Zhai, Bore and Paesani gave "a realistic estimate" of about 198 K and 1,250 atm, and concluded that water "exists in two discernibly distinct liquid states at low temperature and high pressure."[^sciortino2025] Experiments followed. In 2020 a team led by Anders Nilsson heated high-density amorphous ice to 205 ± 10 K, under an internal pressure of 2.5 to 3.5 kbar, and used ultrafast X-ray scattering to watch low-density liquid domains grow over 20 nanoseconds to 3 microseconds, before the sample could crystallize.[^kim2020] In 2026 the same group reported "a crossover from a discontinuous to a continuous transition" and "a rapid increase in the heat capacity consistent with a critical divergence at 210 ± 10 K."[^you2026] They placed the critical point near 210 K (about −63 °C) and 1,000 bar.[^physicstoday2026][^su2026] *Physics Today* noted that the team could not estimate the correlation length of its samples, and quoted Paesani as saying the work "does not close the subject."[^physicstoday2026] Water is not the only example. In 2000 Yoshinori Katayama and colleagues observed a first-order transition in liquid [[Phosphorus|phosphorus]] above about 1 GPa, from a molecular liquid of P₄ units to a polymeric liquid. The change was "sharp and rapid, occurring within a few minutes over a pressure range of less than 0.02 GPa."[^katayama2000] Simulations by Srikanth Sastry and C. Austen Angell found a similar transition in supercooled liquid [[Silicon|silicon]].[^sastry2003] On the Thury spine, the liquid–liquid critical point is the reason the Compendium begins with water. Water may be two liquids, and the [[Phase_diagram|phase diagram]] of the most familiar substance on Earth still held a critical point that was not measured until 2026. ## Microsims — p5.js <div class="microsim-player"> <iframe src="https://wikitube-3d-microsims.netlify.app/Liquid%E2%80%93liquid_critical_point.html" width="100%" height="620" frameborder="0" loading="lazy" sandbox="allow-scripts allow-same-origin" allow="accelerometer; gyroscope" title="Liquid–liquid critical point — p5.js microsim"></iframe> </div> *Microsim (THY-001): drag the state point across the temperature–pressure diagram, or nudge it with the arrow keys. Each cell of the 36 × 36 lattice is a local structure, either low-density liquid (blue) or high-density liquid (amber). Above the critical point the mix changes smoothly along the dashed Widom line. Below it the liquid flips suddenly, with hysteresis, when it crosses the transition line. The critical point sits at the 2026 estimate, about 210 K and 100 MPa. ILLUSTRATIVE: the slope of the transition line, the field coefficients and the "no-man's-land" boundary are not fitted to data.* Videos: [16:9](https://wikitube-3d-microsims.netlify.app/media/Liquid%E2%80%93liquid_critical_point_16x9.mp4) · [9:16](https://wikitube-3d-microsims.netlify.app/media/Liquid%E2%80%93liquid_critical_point_9x16.mp4) ## References [^poole1992]: Poole, Peter H.; Sciortino, Francesco; Essmann, Ulrich; Stanley, H. Eugene (1992). "Phase behaviour of metastable water." *Nature* 360: 324–328. https://doi.org/10.1038/360324a0 [^debenedetti2020]: Debenedetti, Pablo G.; Sciortino, Francesco; Zerze, Gül H. (2020). "Second critical point in two realistic models of water." *Science* 369 (6501): 289–292. https://doi.org/10.1126/science.abb9796 [^sciortino2025]: Sciortino, Francesco; Zhai, Y.; Bore, S. L.; Paesani, Francesco (2025). "Constraints on the location of the liquid–liquid critical point in water." *Nature Physics* 21: 480–485. https://doi.org/10.1038/s41567-024-02761-0 [^kim2020]: Kim, Kyung Hwan; Amann-Winkel, Katrin; Giovambattista, Nicolas; et al. (2020). "Experimental observation of the liquid-liquid transition in bulk supercooled water under pressure." *Science* 370 (6519): 978. https://doi.org/10.1126/science.abb9385 [^you2026]: You, S.; Ladd Parada, M.; Nam, K.; et al. (2026). "Experimental evidence of a liquid-liquid critical point in supercooled water." *Science* 391: 1387. https://doi.org/10.1126/science.aec0018 [^physicstoday2026]: Wells, Sarah (May 7, 2026). "Experiment closes in on a second critical point of water." *Physics Today*. https://physicstoday.aip.org/news/experiment-closes-in-on-a-second-critical-point-of-water [^su2026]: Stockholm University (March 26, 2026). "Experimental discovery of a new critical point in water." EurekAlert!. https://www.eurekalert.org/news-releases/1120965 [^katayama2000]: Katayama, Yoshinori; Mizutani, Takeshi; Utsumi, Wataru; Shimomura, Osamu; Yamakata, Masaaki; Funakoshi, Ken-ichi (2000). "A first-order liquid–liquid phase transition in phosphorus." *Nature* 403: 170–173. https://doi.org/10.1038/35003143 [^sastry2003]: Sastry, Srikanth; Angell, C. Austen (2003). "Liquid–liquid phase transition in supercooled silicon." *Nature Materials* 2: 739–743. https://doi.org/10.1038/nmat994  **Part of the [[WT!Thury_Hydrodynamics_Compendium|Thury Hydrodynamics Compendium]]** — main article for section 7, *Two liquids*. Related sections: [[Properties_of_water]] · [[Hydrogen_bond]] · [[Superfluidity]].   **Microsim — three.js (Wikitube framework):** *Liquid–liquid critical point* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/thury/Liquid–liquid_critical_point.html" data-title="Liquid–liquid critical point"></div> *Built from `MICROSIM_GUIDE/specs/sims/Liquid–liquid_critical_point.json`; part of the [[WT!Thury_Hydrodynamics_Compendium|Thury Hydrodynamics Compendium]] set.*  ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Liquid%E2%80%93liquid_critical_point) : [Wikitube](https://en.wikitube.io/wiki/Liquid%E2%80%93liquid_critical_point) · pinned revision [1327431683](https://en.wikipedia.org/w/index.php?oldid=1327431683) · 2026-09-10 ## Previous hub tags Hubs: `Life_Physics`. Portals: [[PORTAL_Thury_Hydrodynamics_Apex_Spine]], [[PORTAL_Physics]]. --- *Thury main articles, wave 2 · 2026-09-10 · drafted · Compendium section 7 · microsim THY-001 (p5.js, live).*