Molecular Friction Trumps Viscosity in Angstrofluidic Transport.

In the realm of ultra-confined nanofluidics, where channels barely accommodate a single molecule, classical continuum theories would inevitably falter. Fundamental properties like viscosity, wettability, and velocity profiles lose their conventional meaning, leaving a critical gap in our ability to predict and engineer flow at the molecular scale, despite these features continuing to be extrapolated from the underlying molecular behavior. Here, we tackle this conceptual anomaly by probing single-file transport of liquid argon through graphene nanopores and carbon nanotubes via molecular dynamics simulations and interpreting the same from the foundational principles of statistical mechanics as against the traditional approach of continuum property extrapolation. By invoking the ergodic hypothesis, we reconstruct long-time velocity distributions from individual atomic trajectories, enabling the definition of a corresponding viscosity coefficient (CVC) as a continuum-referenced resistance metric rather than a conventional effective viscosity. This physically inspired mapping bridges atomistic realities with continuum surrogates, revealing how flow resistance depends on wall-fluid interactions and confinement-induced geometrical features. Our framework unlocks predictive design tools for sub-nanometer fluidic devices, with significant implications for nanofiltration, ion sieving, and next-generation semiconductor processing, by providing a new lens to translate single-molecule chaos into actionable engineering insight.