Figure Figure1 1 shows the (reduced) P– T phase diagram of all of the systems, as well as the thermodynamic Of the fluid along an isobar P ≈ 1.6 P c the exact value of P forĮach system is listed in the last column in Table 1. Results below focus on the temperature dependence of the properties Parameter for the BOP Te model is determined using a direct MD simulation SW model for Si, and the LJ fluid model are well studied, and theirĬritical parameters can be found in the literature. Properties of the fluid, such as its self-diffusion coefficient. The fraction of the components can also be used to describe the transport As in the case of water, aįast change in the ratio between the two components marks the dynamicalĬrossover, but both components exist on either side of the transition. Intermolecular bonding and the gaslike component with dynamics similar Moreover, we findĮvidence to associate the liquidlike component with the degree of (see the Methods section), the two-componentīehavior is universal in their molecular dynamics. Si, Te, and Lennard-Jones (LJ) fluid-via classical MD simulations.Įven though these systems have very different interatomic potentials Representing four different supercritical fluid systems-water, Work, we aim at answering this question by studying the potentials Is specific to water, whose liquidlike dynamics arises from hydrogenīonds, or can be generalized to other supercritical fluids. Is natural to ask whether the observed two-component dynamics However, remnants of bothĬomponents can be found on either side of the Widom line. It is the ratio between the two components that changes, with a rapidĬrossover observed near the Widom line. Mode between hydrogen-bonded molecules and a low-frequency component Models developed for liquids, but instead can be decomposed into twoĬomponents-a high-frequency component associated with the stretching Contrary to previous approaches, 6, 8 we found that the intermolecular dynamics at a given P, T state cannot be consistently described using Intermolecular dynamics of supercritical water in the region 0.9 < P/ P c < 2.3, 0.6 < T/ T c < 1.2, where P c and T c are theĬritical pressure and temperature. We used both IXS measurements and MD simulations to study the In the deep supercritical region along an extension of the Widom line.Ī region close to the critical point, where the Widom line is veryĬlear. 6 Using classical molecular dynamics (MD) simulations supportedīy inelastic X-ray scattering (IXS) data, they observed a crossover Studies on this topic was done by Simeoni et al. Of supercritical fluids, which should reveal the microscopic mechanismīehind many of the macroscopic properties. Around the Widom line,Ī crossover between liquidlike and gaslike properties is expectedĬlear when it comes to molecular-scale dynamics ![]() ![]() Line indicates rapid changes in the thermodynamic properties of supercriticalįluids, especially in the near-critical region. 3 Although not a rigorous separatrixīetween liquid and gas states, 4 the Widom In particular, the concept of the Widom line hasīeen introduced to refer to the line of maxima of a given responseįunction, such as the isobaric heat capacity, C P. 2 Thus, it is important to understand these properties and their dependenceįluids, which is based on their macroscopic properties, has become Unique properties combining the advantages of liquids (e.g., highĭensities) and gases (e.g., high diffusivities), and these propertiesĪre highly tunable with relatively small changes in temperature, T, and pressure, P. Interesting applications of supercritical fluids fall in the regionĬlose to the critical point. Interest due to their applications in a wide range of chemical and Supercritical fluids have attracted renewed Into the fundamental mechanism controlling the dynamics of supercriticalįluids and highlight the role of spatiotemporally inhomogeneous dynamicsĮven in thermodynamic states where no large-scale fluctuations exist ![]() The ratio between the components can be used toĭescribe important properties of the fluid, such as its self-diffusionĬoefficient, in the transition region. We find evidence to connect the liquidlikeĬomponent dominating at lower temperatures with intermolecular bondingĪnd the component prominent at higher temperatures with free-particle, Leads to a crossover from liquidlike to gaslike dynamics, most rapidlyĪround the Widom line. Of these systems, and the changing ratio between the two components ![]() Two-component behavior is observed in the intermolecular dynamics Study four supercritical fluid systems-water, Si, Te, and Lennard-Jonesįluid-via classical molecular dynamics simulations. Despite the technological importance of supercritical fluids, controversy remainsĪbout the details of their microscopic dynamics.
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