A comprehensive description of capillary flow: Implications of surface curvature

Predicting flow through nanoconduits is essential for the efficient design of integrated nanodevices. Capillary action is a key flow-driving mechanism in nanofluidics, as it requires no external energy supply. However, a comprehensive understanding of nanoscale capillarity has not been achieved. Capillary imbibition in nanoconduits exhibits different stages: an initial inviscid regime characterized by constant velocity during the early time of imbibition; a subsequent visco-inertial regime, where viscous losses gradually decelerate the flow; and finally, a viscous regime, in which inertia becomes negligible, and viscosity fully governs the imbibition. Descriptions of these regimes typically focus on the effect of dynamic contact angle and the effective viscosity. Nevertheless, as nanoconduit dimensions decrease, changes in meniscus curvature alter the surface tension, thereby affecting flow predictions. In this study, all-atom molecular dynamics simulations are employed to develop a comprehensive model that captures the effects of interfacial curvature on the surface tension during capillary imbibition in nanoconfinement.