Experimental investigation of Poiseuille flows in nanochannels

Poiseuille flows in nanoconfinements play fundamental roles in nanofluidics, which has great potential applications in nanoscale devices. In the past decades, studies of nanoscale flows have been mainly focused on molecular dynamics simulations. Experimental investigations have recently been gaining attention due to the advances in nanofabrication. In the nanoscale, the stick boundary condition assumed in the classic fluid mechanics tends to break down while flow slip emerges as a popular phenomenon. The enhanced flow caused by the velocity slip has been intensively investigated for water in recent years. However, many of the reported results are controversial and the real mechanism still remains unclear. In this work, we examine the Poiseuille flow of water in 100 nm channels for a wide range of pressure drops. It is found that the dependence of the flow rate on the pressure drop falls into three regimes, i.e., two linear regimes at low and high pressure drops and a transition regime in between. The flow rate at lower pressure drops is found slightly smaller than the theoretical predictions, which is consistent with some previous experimental results. For high pressure drops, the slip length tends to reach a limit and remains unchanged. A slip length of 3.9 nm is obtained in this regime, which enhances the flowrate by about 22%. The mechanism for the transition regime is also investigated.