Flow Behaviors And Transport Mechanism Of Fluids In The Black Phosphorus Nanotube

The properties and application of low-dimensional materials is one of the hottest research fields currently.Black phosphorus,a new two-dimensional material,has attracted widespread attention because of its excellent performance,and black phosphorus nanotube is considered to be formed by winding the single layer black phosphorus.In this paper,the flow behaviors and transport mechanism of fluids in the black phosphorus nanotube were studied by the molecular dynamics method.The results will provide a theoretical basis for the application of the black phosphorus nanotube in the transport of fluids.The axial transport properties of water molecules in the rotating black phosphorus nanotube were studied by the molecular dynamics method,and the mechanism was analyzed based on the liquid-solid interface.The results show that water molecules in the rotating chiral black phosphorus nanotube can transport along the axial direction,and the moving direction of water molecules is determined by the rotating direction of the nanotube.The velocity of water molecules as well as the acting force of water molecules received from the nanotube in the axial direction increase with the increase of the angular velocity.The properties of the liquid-solid interface were analyzed by using Couette flow model,and it is clarified that the natural fold structure on the surface of the black phosphorus nanotube is the essential reason of the axial transport of water molecules in the nanotube.Besides,we constructed a model of filling water molecules between two rotating nanotubes.It is found that the transport capacity of water molecules between two nanotubes will be enhanced when the inner and outer tube rotate simultaneously.At last,the axial motion properties of water molecules in the rotating chiral black phosphorus nanotube affected by the factors as radius,temperature and number of layers were investigated.The radius of the nanotubes will affect the directional transport of water molecules.Specifically,at the same angular velocity of the nanotube,with the increase of the radius,the velocity of water molecules will decrease,while the applied force will increase.When the temperature is lower than the normal temperature the velocity and the applied force of water molecules will increase with the increase of the temperature,and when the temperature reaches the normal temperature it will become stable.The axial transport of water molecules in the double-walled black phosphorus nanotube is little different from that in the single-walled black phosphorus nanotube,which proves that the number of layers has no significant influence on the transport properties of water molecules.The pressure-driven transport behaviors of water molecules in the black phosphorus nanotube and the influence of the relevant parameters were studied based on the Poiseuille flow model.It is found that the velocity of water molecules in the areas with different radial distance from tuber center different.The boundary slip velocity and the mean velocity of water will increase with the increase of the driving force.Under the same driving force,the increase of the chiral angle of the nanotube will cause the decrease of the transport velocity and the increase of the liquid-solid interface friction coefficient,the reason of which is the natural fold structure on the surface of the nanotube.Finally,the effect of radius,temperature and number of layers were investigated.The results show that with the increase of nanotube radius,the boundary slip velocity and the mean velocity of the water molecules will increase,while the interface friction coefficient is basically unchanged.The increase of temperature will cause the increase of the transport velocity of water molecules and the slight decrease of the interface friction coefficient.Compared with the motion of water molecules in the single-walled black phosphorus nanotube,the boundary slip velocity and the mean velocity of water molecules in the double-walled black phosphorus nanotube will decrease,while the interface friction coefficient will increase slightly.