Universal scaling of position-dependent self-diffusion in confined fluids

Self-diffusion in confined fluids is known to vary significantly near solid boundaries due to molecular layering, energy dissipation, and structural reorganization. Using molecular dynamics simulations, we show that this position-dependent diffusivity can be quantitatively described by a sigmoidal scaling function governed by the molecular mean free path ($\lambda$) and kinetic energy ($E_K$ ). Across a wide range of thermodynamic conditions, the local diffusivity profiles collapse onto a universal master curve when normalized by near-wall suppression and far-field recovery scales. This finding reveals a transferable relation linking microscopic transport modulation to confinement geometry and energy input. These results establish a predictive framework for near-wall transport and provide insights for multiscale modeling in confined fluids.