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Zigzagging diffusion and nonstandard transport in particle-laden nanopores under extreme confinement

Andreas Baer1, Paolo Malgaretti2,*, Kevin Höllring1, Jens Harting1,2,3, and Ana-Sunčana Smith1,4,†

  • *Contact author: p.malgaretti@fz-juelich.de
  • †Contact author: smith@physik.fau.de; asmith@irb.hr
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Phys. Rev. Research 7, 043251 – Published 3 December, 2025

DOI: https://doi.org/10.1103/jjrg-b6rg

Abstract

Understanding transport subject to molecular-scale confinement is key to advancing nanofluidics, yet classical hydrodynamic laws often fail at these scales. Here, we study a model system: transport of toluene as a solvent and small fullerenes as model particles confined within alumina slit nanopores using molecular dynamics simulations. We find that toluene organizes into discrete layers whose commensurability with the pore width leads to a striking, nonmonotonic, zigzag dependence of transport coefficients on confinement. This layering drives oscillations not only in solvent diffusivity but also in flow velocity and permeability under pressure-driven conditions, breaking the expected scaling relations between diffusion, viscosity, and flow. Surprisingly, introducing a nanoparticle does not wash out these effects—although the fullerene perturbs local layering, the nanoparticle diffusivity retains a zigzag dependence on pore width. Our results demonstrate how structural commensurability and interfacial effects dominate transport in nanoconfined liquids and lead to important deviations from continuum expectations. These findings establish a microscopic basis for size-dependent transport in nanopores and highlight the need for beyond-hydrodynamic models in confined soft matter systems.

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Phys. Rev. Research 7, 043251– Published 3 December, 2025
  • Received 16 June 2025
  • Accepted 9 September 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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