Graphene-based thermal pump to enable continuous water flow through slit nanochannels: The Role of Flexural Phonons*

In this study, by performing all-atom Non-Equilibrium Molecular Dynamics simulations, we propose a graphene-based thermal nanopump which produces controlled and continuous water flow in nanoslit channels. Upon systematically imposing thermal gradients, a significant net fluid flow towards the low-temperature zone is measured in all cases. The present nanopump produces water flow with average velocities up to 3 m/s. We find that the water flow rates increase due to an enhancement of the wall thermal rippling as higher temperature gradients are imposed. Moreover, vibrational and phonon Density-of-States analyses on graphene walls reveal that the out-of-plane flexural phonons are responsible for the water flow production. We notice that lower frequency phonon branches are activated with higher imposed temperature gradients. This study provides the basis for developing a functional thermal pumping system based on sheets of graphene, which is capable to produce continuous water flow in nanofluidic conduits, opening the door to practical exploitation of thermal gradients for fluid transport in integrated nanofluidic devices.