A Comprehensive model of water capillarity in nanochannels: an atomistic study

An important bottleneck in the design of integrated nanodevices arises from predicting flow rates throughout the nanoconduit networks connecting the functional stages of the platform. Capillary action is a key flow driving mechanism in nanofluidics. Spontaneous capillary filling of water in nanochannels follows a purely inviscid regime with constant velocity during the first stage of imbibition. Subsequently, the capillary kinetics evolves in a developing flow where the Laplace capillary force is balanced by varying contributions from inertia and viscous losses. As the filling length becomes sufficiently large, the inertial resisting effect on the imbibition vanishes and a purely viscous flow is attained. Moreover, during inertial and visco-inertial regimes, the developing capillary meniscus displays a time varying contact angle which converges in a dynamic contact angle which characterizes the viscous regime. In this study, all-atom large scale MD simulations are employed to obtain a comprehensive model to describe the transition from inertial to viscous flow regimes of capillarity in silica nanochannels. The present model considers the time varying initial contact angle during the visco-inertial regime and the dynamic contact angle reached during the viscous regime as the filling becomes independent of inertial effects.