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Skarmoutsos I. Substantial breakdown of the hydrogen-bonding network, local density inhomogeneities and fluid-liquid structural transitions in supercritical octanol-1: A molecular dynamics investigation. J Chem Phys 2024; 161:044506. [PMID: 39056384 DOI: 10.1063/5.0219417] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2024] [Accepted: 07/11/2024] [Indexed: 07/28/2024] Open
Abstract
Molecular dynamics simulations have been employed to explore the hydrogen-bonding structure and dynamics in supercritical octanol-1 at a near-critical temperature and up to high densities and pressures. A substantial breakdown of the hydrogen-bonding network when going from ambient-liquid to supercritical conditions is revealed. The fraction of the non-hydrogen bonded molecules significantly increases in supercritical octanol-1, and a substantial decrease in the intermittent hydrogen-bond lifetime is observed. This behavior is also reflected on the maximum local density augmentation, which is comparable to the values obtained for non-polar and non-hydrogen bonded fluids. The existence of a structural transition from an inhomogeneous fluid phase to a soft-liquid one at densities higher than 2.0 ρc is also revealed. At higher densities, a significant change in the reorientational relaxation process is observed, reflected on the significant increase in the ratio of the Legendre reorientational times τ1R/τ2R. The latter becomes much higher than the value predicted by the Debye model of diffusive reorientation and the corresponding ratio for ambient liquid octanol-1. The non-polar tail of octanol-1 under supercritical conditions reorients more slowly in comparison with the polar tail. Interestingly, the opposite behavior is observed for the ambient liquid, further verifying the strong effect of the breakdown of the hydrogen bonding network on the properties of supercritical octanol-1. In accordance with the above-mentioned findings, the static dielectric constant of supercritical octanol-1 is very low even at high densities and pressures, comparable to the values obtained for non-polar and non-hydrogen bonded fluids.
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Affiliation(s)
- Ioannis Skarmoutsos
- Laboratory of Physical Chemistry, Department of Chemistry, University of Ioannina, 45110 Ioannina, Greece
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Ranieri U, Formisano F, Gorelli FA, Santoro M, Koza MM, De Francesco A, Bove LE. Crossover from gas-like to liquid-like molecular diffusion in a simple supercritical fluid. Nat Commun 2024; 15:4142. [PMID: 38755136 PMCID: PMC11099187 DOI: 10.1038/s41467-024-47961-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Accepted: 04/15/2024] [Indexed: 05/18/2024] Open
Abstract
According to textbooks, no physical observable can be discerned allowing to distinguish a liquid from a gas beyond the critical point. Yet, several proposals have been put forward challenging this view and various transition boundaries between a gas-like and a liquid-like behaviour, including the so-called Widom and Frenkel lines, and percolation line, have been suggested to delineate the supercritical state space. Here we report observation of a crossover from gas-like (Gaussian) to liquid-like (Lorentzian) self-dynamic structure factor by incoherent quasi-elastic neutron scattering measurements on supercritical fluid methane as a function of pressure, along the 200 K isotherm. The molecular self-diffusion coefficient was derived from the best Gaussian (at low pressures) or Lorentzian (at high pressures) fits to the neutron spectra. The Gaussian-to-Lorentzian crossover is progressive and takes place at about the Widom line intercept (59 bar). At considerably higher pressures, a liquid-like jump diffusion mechanism properly describes the supercritical fluid on both sides of the Frenkel line. The present observation of a gas-like to liquid-like crossover in the self dynamics of a simple supercritical fluid confirms emerging views on the unexpectedly complex physics of the supercritical state, and could have planet-wide implications and possible industrial applications in green chemistry.
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Affiliation(s)
- Umbertoluca Ranieri
- Dipartimento di Fisica, Università di Roma La Sapienza, Piazzale Aldo Moro 5, Roma, 00187, Italy
- Centre for Science at Extreme Conditions and School of Physics and Astronomy, University of Edinburgh, Edinburgh, EH9 3FD, UK
| | - Ferdinando Formisano
- CNR - Istituto Officina dei Materiali (IOM), Grenoble, INSIDE@ILL, 71 Avenue des Martyrs, Grenoble, Cedex 9, France.
- Institut Laue-Langevin, 71 Avenue des Martyrs, Grenoble, Cedex 9, France.
| | - Federico A Gorelli
- Center for High Pressure Science and Technology Advanced Research (HPSTAR), 1690 Cailun Road, Shanghai, 201203, China.
- Shanghai Advanced Research in Physical Sciences (SHARPS), Pudong, Shanghai, 201203, China.
- Consiglio Nazionale delle Ricerche, Istituto Nazionale di Ottica, CNR-INO, Via Nello Carrara 1, Sesto Fiorentino (FI), 50019, Italy.
| | - Mario Santoro
- Consiglio Nazionale delle Ricerche, Istituto Nazionale di Ottica, CNR-INO, Via Nello Carrara 1, Sesto Fiorentino (FI), 50019, Italy
- European Laboratory for Nonlinear Spectroscopy, LENS, Via Nello Carrara 1, Sesto Fiorentino (FI), 50019, Italy
| | - Michael Marek Koza
- Institut Laue-Langevin, 71 Avenue des Martyrs, Grenoble, Cedex 9, France
| | - Alessio De Francesco
- CNR - Istituto Officina dei Materiali (IOM), Grenoble, INSIDE@ILL, 71 Avenue des Martyrs, Grenoble, Cedex 9, France
- Institut Laue-Langevin, 71 Avenue des Martyrs, Grenoble, Cedex 9, France
| | - Livia E Bove
- Dipartimento di Fisica, Università di Roma La Sapienza, Piazzale Aldo Moro 5, Roma, 00187, Italy
- Laboratory of Quantum Magnetism, Institute of Physics, École Polytechnique Fédérale de Lausanne, Lausanne, CH-1015, Switzerland
- Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Sorbonne Université, UMR CNRS 7590, 5 Place Jussieu, Paris, 75005, France
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Simeski F, Ihme M. Supercritical fluids behave as complex networks. Nat Commun 2023; 14:1996. [PMID: 37032390 PMCID: PMC10083177 DOI: 10.1038/s41467-023-37645-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Accepted: 03/22/2023] [Indexed: 04/11/2023] Open
Abstract
Supercritical fluids play a key role in environmental, geological, and celestial processes, and are of great importance to many scientific and engineering applications. They exhibit strong variations in thermodynamic response functions, which has been hypothesized to stem from the microstructural behavior. However, a direct connection between thermodynamic conditions and the microstructural behavior, as described by molecular clusters, remains an outstanding issue. By utilizing a first-principles-based criterion and self-similarity analysis, we identify energetically localized molecular clusters whose size distribution and connectivity exhibit self-similarity in the extended supercritical phase space. We show that the structural response of these clusters follows a complex network behavior whose dynamics arises from the energetics of isotropic molecular interactions. Furthermore, we demonstrate that a hidden variable network model can accurately describe the structural and dynamical response of supercritical fluids. These results highlight the need for constitutive models and provide a basis to relate the fluid microstructure to thermodynamic response functions.
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Affiliation(s)
- Filip Simeski
- Department of Mechanical Engineering, Stanford University, Stanford, CA, 94305, USA
| | - Matthias Ihme
- Department of Mechanical Engineering, Stanford University, Stanford, CA, 94305, USA.
- Department of Photon Science, SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.
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