Anomalous Flow Behavior in Nanochannels: A Molecular Dynamics Study

We report molecular dynamics simulations of flow of water in nanochannels with a range of surface wettability characteristics (hydrophobic to strongly hydrophilic) and driving forces (pressures). Our results show apparently anomalous behavior. At low pressures, the rate is higher in nanochannels with hydrophilic surfaces than that with hydrophobic surfaces; however, with high pressure driven flow we observe opposite trends. This apparently anomalous behavior can be explained on the basis of molecular thermodynamics and fluid mechanics considerations. We have also investigated in detail the effect of surface wettability on the resistance to flow in nanochannels and how this varies with the flow velocity. Understanding such behavior is important in many nanofluidic devices such as nanoreactors, nanosensors, and nanochips that are increasingly being designed and used.