Evidence of caged to normal diffusion transition in benzene along supercritical isobars: Insights from molecular dynamics simulations

W Silva-Oliveira and EE de Moraes and TPO Nogueira and DA Sales and JR Bordin, JOURNAL OF SUPERCRITICAL FLUIDS, 203, 106094 (2023).

DOI: 10.1016/j.supflu.2023.106094

Understanding the behavior of supercritical fluids holds both fundamental and practical significance. From a practical standpoint, these fluids find numerous technological applications across environmental, mechan-ical, chemical, biological, and geothermal industries. However, from a fundamental scientific perspective, unraveling the intricate structure, thermodynamics, and dynamics of supercritical fluids remains an ongoing challenge. In this work, we address this task by employing NPT molecular dynamics simulations on a rigid benzene model under high pressures. Our observations reveal a striking dynamical transition, with a caged regime at low temperatures and a normal diffusion regime at high temperatures. Notably, the subdiffusive region aligns with the compressible region from the experimental phase diagram, while the normal diffusion occurs in the supercritical region. Furthermore, we present compelling evidence linking the subdiffusion to a caged trajectory and illustrate how uncaging and clustering play a key role in the dynamical transition. The identification of the subdiffusive and normal diffusion regimes provides valuable information for optimizing processes involving supercritical fluids in various industries. Moreover, the link between caged trajectories and dynamical transitions adds a new dimension to our understanding of molecular behavior in supercritical systems.

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