Interface nanoparticle control of a nanometer water pump

Nanoparticles are highly versatile and exhibit broad applications in tuning material properties. Herein, we show through molecular dynamics simulations the possibility of a nanometer water pump, driven by the motion of nanoparticles (NPs) on a membrane surface. Surprisingly, considerable net water flux can be induced through a carbon nanotube (CNT) that is perpendicular to the NP motion. The water transport can occur in a highly controllable fashion, not only by using a single NP with different forces, but also by varying the CNT length or the NP number. Specifically, for a single NP, the water flow and flux are found to increase linearly with an increase in force, following the same behavior of NP velocity. Inversely, the water translocation time exhibits a linear decrease. We further revealed the unique relation between the water flow and occupancy divided by the translocation time. The CNT length can significantly screen the thermal fluctuation of an outside water reservoir, leading to an increase in the water flux and subsequent unidirectional transport. More interestingly, under moderate force, the water flow and flux demonstrate maximum behaviors with an increase in NP number, co-determined by the NP velocity and water occupancy. The maximum location shifts to the lower NP number region for a larger force. We also identify two CNT states that correspond to low water flow. Our results provide a significant new method to pump water molecules through a CNT channel, which is helpful for the design of controllable nanofluidic devices.