Research On Nanoconfined Water Transport Based On Molecular Dynamics

Water is an indispensable resource for all living things on earth and plays a vital role in the process of human development.In recent years,it has been found that the excellent performance of water molecules transport in micro and narrow channels with limited space can be applied to the fields of bio-medicine,aerospace,seawater desalination and microbial fuel cells.At the nanoscale,many macroscopic physical theories are no longer applicable,and due to the small size,experimental research on the transport of water molecules in nanometer confined channels has great difficulties.Therefore,molecular dynamics simulation has become the best choice to study the physical and chemical properties and flow state of water molecules in nanometer confined channels.Nanoscale channels are the main carriers of nano-confined water flow.The flow behavior of water molecules in microscopic channels usually presents a completely different form from the traditional macroscopic fluid theory.This paper is based on molecular dynamics(MD)method,the dynamic behavior and physical characteristics of a series of water molecules transported in a confined system with different structures are simulated by using carbon nanotubes and graphene as the carrier.In the first part,carbon nanotubes with different chiral indices are immersed into the slit of graphene containing water molecules to simulate the microscopic behavior of water molecules in the system.The simulation results show that the changes of temperature and chiral index of carbon nanotubes have direct influence on the diffusion behavior and arrangement structure of water molecules in the system.The increase of temperature in the system and the chiral index of carbon nanotubes will lead to the increase of the movement speed and the diffusion coefficient of water molecules,as well as the decrease of the order of water molecules in the system.The water storage capacity of carbon nanotubes is directly related to the temperature of the system.The increase of temperature will lead to the decrease of the water storage capacity of carbon nanotubes.In the second part,graphene slit channels with coarse folds in a variety of structures are selected to simulate the molecular dynamics of water transported in rough graphene slits with different fold shapes,fold sizes and intercalation widths.The simulation results show that,the shape of the rough folds and the width of the interlayer will affect the diffusion ability and structure distribution of water molecules in the slit to different degrees.Compared with smooth graphene slits,rough folds would increase the diffusion ability of water molecules in the slits.Square rough folds are more conducive to the diffusion of water molecules in graphene slits than equilateral triangle rough folds.The number density distribution of water molecules in the slit is related to the size of rough folds on graphene sheets.In the third part,a kind of carbon nanotubes with defects are selected to simulate the transport properties and distribution of water molecules in the carbon nanotube with defects under a confined system.Through the simulation comparison,it is found that when defects of the same length appear in different positions in the tube,the maximum diffusion coefficient can differ by more than 70%.When the defect appears at the end of the carbon nanotube,the stability is the strongest.The position of the defect can restrict the flow of water molecules in the carbon nanotube.This paper can provide theoretical support for the application fields of micro-nano fluid mechanical devices,aerospace and seawater desalination by studying the transport behavior of water molecules in nanometer confined channels,which has certain academic significance and application value.