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1. Liquid–liquid phase separation in artificial cells

   https://doi.org/10.1098/rsfs.2018.0032  

   Crowe, Charles D.; Keating, Christine D. (August 2018, Interface Focus)
2. Liquid–liquid transition kinetics in D-mannitol

   https://doi.org/10.1063/5.0097865  

   Cao, Chengrong; Tang, Wei; Perepezko, John H. (August 2022, The Journal of Chemical Physics)

   The kinetics of the first order liquid–liquid transition (LLT) in a single-component liquid D-mannitol have been examined in detail by the high rate of flash differential scanning calorimetry measurements. By controlling the annealing temperature, the phase X formation from the supercooled liquid is distinguished by either a nucleation-growth or a spinodal-decomposition type of LLT. In the measured time–temperature-transformation curve the portion covering the nucleation-growth type of LLT can be well fitted with a classical nucleation theory analysis. 

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3. Evidence of a liquid–liquid transition in a glass-forming ionic liquid

   https://doi.org/10.1073/pnas.2020878118  

   Harris, Matthew A.; Kinsey, Thomas; Wagle, Durgesh V.; Baker, Gary A.; Sangoro, Joshua (March 2021, Proceedings of the National Academy of Sciences)

   A liquid–liquid transition (LLT) is a transformation from one liquid to another through a first-order transition. The LLT is fundamental to the understanding of the liquid state and has been reported in a few materials such as silicon, phosphorus, triphenyl phosphite, and water. Furthermore, it has been suggested that the unique properties of materials such as water, which is critical for life on the planet, are linked to the existence of the LLT. However, the experimental evidence for the existence of an LLT in many molecular liquids remains controversial, due to the prevalence and high propensity of the materials to crystallize. Here, we show evidence of an LLT in a glass-forming trihexyltetradecylphosphonium borohydride ionic liquid that shows no tendency to crystallize under normal laboratory conditions. We observe a step-like increase in the static dielectric permittivity at the transition. Furthermore, the sizes of nonpolar local domains and ion-coordination numbers deduced from wide-angle X-ray scattering also change abruptly at the LLT. We independently corroborate these changes in local organization using Raman spectroscopy. The experimental access to the evolution of local order and structural dynamics across a liquid–liquid transition opens up unprecedented possibilities to understand the nature of the liquid state. 

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4. Liquid–liquid criticality in the WAIL water model

   https://doi.org/10.1063/5.0099520  

   Weis, Jack; Sciortino, Francesco; Panagiotopoulos, Athanassios Z.; Debenedetti, Pablo G. (July 2022, The Journal of Chemical Physics)

   The hypothesis that the anomalous behavior of liquid water is related to the existence of a second critical point in deeply supercooled states has long been the subject of intense debate. Recent, sophisticated experiments designed to observe the transformation between the two subcritical liquids on nano- and microsecond time scales, along with demanding numerical simulations based on classical (rigid) models parameterized to reproduce thermodynamic properties of water, have provided support to this hypothesis. A stronger numerical proof requires demonstrating that the critical point, which occurs at temperatures and pressures far from those at which the models were optimized, is robust with respect to model parameterization, specifically with respect to incorporating additional physical effects. Here, we show that a liquid–liquid critical point can be rigorously located also in the WAIL model of water [Pinnick et al., J. Chem. Phys. 137, 014510 (2012)], a model parameterized using ab initio calculations only. The model incorporates two features not present in many previously studied water models: It is both flexible and polarizable, properties which can significantly influence the phase behavior of water. The observation of the critical point in a model in which the water–water interaction is estimated using only quantum ab initio calculations provides strong support to the viewpoint according to which the existence of two distinct liquids is a robust feature in the free energy landscape of supercooled water. 

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5. Polyamorphism and liquid-liquid transformations in D-mannitol

   https://doi.org/10.1063/1.5041757  

   Tang, W.; Perepezko, J. H. (August 2018, The Journal of Chemical Physics)