Slip-Flow Regimes in Nanofluidics: A Universal Superexponential Model

Many experiments have shown large flow-enhancement ratios (up to 105) in carbon nanotubes (CNTs) with diameters larger than 5 nm. However, molecular-dynamics simulations have never replicated these results maintaining a 3-orders-of-magnitude gap with measurements. Our study provides a generic model of nanofluidics for continuum slip flow (diameter > 3 nm) that fills this significant gap and sheds light on its origin. Compared to 140 literature cases, the model explains the entire range of experimental flow enhancements by changes of nanotube diameters and finite variations of interfacial energies. Despite large variations of flow-enhancement ratios spanning 5 orders of magnitude in experimental results, the ratio between these data and corresponding model predictions approaches unity for the majority of experiments. The role of viscous entrance effects is discussed. The model provides insight into puzzling observations such as differences of CNTs and boron-nitride nanotubes, the slip on low-contact-angle surfaces and massive functionalization effects. This study could advance our understanding of nanoscale transport mechanisms and aid the design of tailored nanomembranes.