Pressure-induced water flow through model nanopores

Abstract

This paper describes nonequilibrium molecular dynamics simulations of pressure induced transport of liquid water through model nanopores. We consider a simple model for a porous membrane consisting of a slab of water molecules held in a rigid ice structure and penetrated by a pore of nanometer scale dimensions. Both hydrophilic membranes composed of conventional TIP3P water and hydrophobic membranes consisting of modified water with the model partial charges set to zero are treated. Molecular dynamics simulation is employed to investigate the rate of water flow through the pore induced by a pressure difference across the membrane. The results are compared with the predictions of continuum hydrodynamics. We find that the flow rate of water through hydrophilic pores is much less than the continuum predictions, while the flux through hydrophobic pores can significantly exceed the continuum theory. Finally, we show asymmetric behavior in the flux vs. pressure difference for a conical nanopore, which thus acts as a Brownian ratchet.