Redefining flow regimes in sub-nanometer carbon channels under life-scale confinement

Non-continuum transport at the nanoscale reorganizes molecular dynamics by altering viscosity gradients, energy landscapes, and interfacial interactions, thereby accelerating mass transfer and reaction kinetics. Comparable phenomena occur in biological nanopores, such as ion channels and aquaporins, where confinement enables essential life-sustaining transport. In carbon nanotubes (CNTs) and other angstrom-scale channels, confinement induces molecular ordering, redistributes interfacial energies, and restricts diffusivity, lowering activation barriers, and enhancing directional transport efficiency. Motivated by these biological analogues, we employ molecular dynamics simulations to systematically compare sub-nanometer CNTs and rectangular channels, resolving the coupled influence of geometry, confinement, and interfacial forces on fluid behavior. CNTs exhibit substantially higher flow velocities and lower effective viscosities than rectangular channels due to strong van der Waals interactions, reduced interfacial friction, and the emergence of single-file molecular transport, leading to distinct deviations from continuum hydrodynamics. Rectangular channels, in contrast, support plug-like flow with elevated viscosities, highlighting the dominant role of wall–fluid coupling. Free-energy and friction analyses reveal that although CNTs present higher free-energy barriers, their molecular arrangement enables exceptionally rapid transport. These findings provide direct molecular-scale evidence of how confinement geometry governs transport at biologically relevant scales and establish a physics-based framework for mesoscopic models of non-continuum flows.