Molecular Dynamics Study of Mass Transport Behavior in Nano-Confined Supercritical Water-Short-Chain Alkane Mixtures

Mass transport properties of nano-confined fluids play a crucial role in energy and chemical engineering applications. This study employs all-atom molecular dynamics simulations to investigate the diffusion behavior and microstructural features of supercritical water-short-chain alkane binary mixtures within carbon nanotubes of varying diameters (1.220–3.932 nm) at different temperatures (673.15 K–1073.15 K). By analyzing the self-diffusion coefficients, hydrogen bond networks, energy distributions, and radial density profiles of solute molecules, we elucidated the regulatory mechanisms of temperature and spatial confinement on mass transport. The results demonstrate that fluids exhibit pronounced confined diffusion characteristics in narrow carbon nanotubes (diameter<2.034 nm), while the transport behavior gradually approaches the properties of bulk fluids when CNT diameter exceeds 3.526 nm. Temperature influences mass transport of nano-confined fluids by disrupting the hydrogen bond network of supercritical water (81.16% reduction), enhancing molecular thermal motion, and altering the spatial distribution of solutes.