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1. The effect of polymer length in liquid-liquid phase separation

   https://doi.org/10.1016/j.xcrp.2023.101415  

   Valdes-Garcia, Gilberto; Gamage, Kasun; Smith, Casey; Martirosova, Karina; Feig, Michael; Lapidus, Lisa J. (May 2023, Cell Reports Physical Science)
2. Anomalous properties in the potential energy landscape of a monatomic liquid across the liquid–gas and liquid–liquid phase transitions

   https://doi.org/10.1063/5.0106923  

   Zhou, Yang; Lopez, Gustavo E.; Giovambattista, Nicolas (September 2022, The Journal of Chemical Physics)

   As a liquid approaches the gas state, the properties of the potential energy landscape (PEL) sampled by the system become anomalous. Specifically, (i) the mechanically stable local minima of the PEL [inherent structures (IS)] can exhibit cavitation above the so-called Sastry volume, v S , before the liquid enters the gas phase. In addition, (ii) the pressure of the liquid at the sampled IS [i.e., the PEL equation of state, P IS ( v)] develops a spinodal-like minimum at v S . We perform molecular dynamics simulations of a monatomic water-like liquid and verify that points (i) and (ii) hold at high temperatures. However, at low temperatures, cavitation in the liquid and the corresponding IS occurs simultaneously and a Sastry volume cannot be defined. Remarkably, at intermediate/high temperatures, the IS of the liquid can exhibit crystallization, i.e., the liquid regularly visits the regions of the PEL that belong to the crystal state. The model liquid considered also exhibits a liquid–liquid phase transition (LLPT) between a low-density and a high-density liquid (LDL and HDL). By studying the behavior of P IS ( v) during the LLPT, we identify a Sastry volume for both LDL and HDL. The HDL Sastry volume marks the onset above which IS are heterogeneous (composed of LDL and HDL particles), analogous to points (i) and (ii) above. However, the relationship between the LDL Sastry volume and the onset of heterogeneous IS is less evident. We conclude by presenting a thermodynamic argument that can explain the behavior of the PEL equation of state P IS ( v) across both the liquid–gas phase transition and LLPT. 

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3. 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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4. Emulsion patterns in the wake of a liquid–liquid phase separation front

   https://doi.org/10.1073/pnas.1716330115  

   Moerman, Pepijn G.; Hohenberg, Pierre C.; Vanden-Eijnden, Eric; Brujic, Jasna (April 2018, Proceedings of the National Academy of Sciences)
5. The gas|liquid interface eclipses the liquid|liquid interface for glucose oxidase rate acceleration in microdroplets

   https://doi.org/10.1073/pnas.2416353121  

   Krushinski, Lynn E; Herchenbach, Patrick J; Dick, Jeffrey E (December 2024, Proceedings of the National Academy of Sciences)

   The curious chemistry observed in microdroplets has captivated chemists in recent years and has led to an investigation into their ability to drive seemingly impossible chemistries. One particularly interesting capability of these microdroplets is their ability to accelerate reactions by several orders of magnitude. While there have been many investigations into which reactions can be accelerated by confinement within microdroplets, no study has directly compared reaction acceleration at the liquid|liquid and gas|liquid interfaces. Here, we confine glucose oxidase, one of life’s most important enzymes, to microdroplets and monitor the turnover rate of glucose by the electroactive cofactor, hexacyanoferrate (III). We use stochastic electrochemistry to monitor the collision of single femtoliter water droplets on an ultramicroelectrode. We also develop a measurement modality to robustly quantify reaction rates for femtoliter liquid aerosol droplets, where the majority of the interface is gas|liquid. We demonstrate that the gas|liquid interface accelerates enzyme turnover by over an order of magnitude over the liquid|liquid interface. This is the first apples-to-apples comparison of reaction acceleration at two distinct interfaces that indicates that the gas|liquid interface plays a central role in driving curious chemistry. 

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