Confinement-Controlled Cluster Percolation Shifts the Widom Crossover in Supercritical Methane
Abstract
Supercritical fluids undergo significant structural and dynamic changes near the Widom line, which separates gas-like and liquid-like regimes. These phenomena are well understood for bulk fluids, but their evolution under nanoscale confinement remains poorly understood. Using a Grand Canonical Monte Carlo and Molecular Dynamics simulation framework, we show that confinement of supercritical CH4 in clay slit nanopores shifts the Widom crossover to lower pressures, with the shift increasing as pore size decreases. Energy-based cluster analysis reveals that this shift is associated with the emergence of system-spanning molecular clusters. Confinement promotes the percolation of these clusters at lower pressures, extending liquid-like behaviour into regimes that are gas-like under bulk conditions. The crossover is also reflected in transport properties as an inflection in both the effective mean distance between free molecules and clusters and the molecular diffusion coefficient. These results establish a direct link between confinement-controlled cluster percolation and the Widom crossover.
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BibTeX
@misc{najafimarghmaleki2026confinementcontrolled,
title = {{Confinement-Controlled Cluster Percolation Shifts the Widom Crossover in Supercritical Methane}},
author = {Adel Najafimarghmaleki and Paola Carbone},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15010314/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010314/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Confinement-Controlled Cluster Percolation Shifts the Widom Crossover in Supercritical Methane
AU - Adel Najafimarghmaleki
AU - Paola Carbone
PY - 2026
DA - 2026/10/12
PB - ChemRxiv
DO - 10.26434/chemrxiv.15010314/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010314/v1
AB - Supercritical fluids undergo significant structural and dynamic changes near the Widom line, which separates gas-like and liquid-like regimes. These phenomena are well understood for bulk fluids, but their evolution under nanoscale confinement remains poorly understood. Using a Grand Canonical Monte Carlo and Molecular Dynamics simulation framework, we show that confinement of supercritical CH4 in clay slit nanopores shifts the Widom crossover to lower pressures, with the shift increasing as pore size decreases. Energy-based cluster analysis reveals that this shift is associated with the emergence of system-spanning molecular clusters. Confinement promotes the percolation of these clusters at lower pressures, extending liquid-like behaviour into regimes that are gas-like under bulk conditions. The crossover is also reflected in transport properties as an inflection in both the effective mean distance between free molecules and clusters and the molecular diffusion coefficient. These results establish a direct link between confinement-controlled cluster percolation and the Widom crossover.
ER -