Molecular Dynamics Simulation And Experimental Research On Particle Transport In Nanochannels

With the progress and innovation of Science and Technology,natural science and engineering technology are developing toward nano-scale and miniaturization,and nanofluidic technology is gradually being researched,it has broad development and application prospects in applied biology,information processing,diagnostic technology,and other fields.Unlike at the macro-scale,the transport properties of matter and the distribution of ions will change at the nano-scale,resulting in many unique phenomena,probing into the essential reasons behind these phenomena can play an active role in promoting the development and application of micro-nano-chips.In this paper,the phenomena and laws of ion transport in boron nitride nanotubes were studied by the Molecular dynamics simulation method,and a four-probe test rig was designed to verify and analyze the simulation results.The main research contents are as follows:A cylindrical boron nitride nanotube model with a diameter of 2 nm was developed using Nanotube Modeler,the effects of electrolyte concentration,wall Charge density,and electric field strength on ion transport in BNNTs were studied by Molecular dynamics simulation.It is found that the ionic current increases linearly with the increase of electrolyte concentration when the electrolyte concentration is between 0.3 m and 0.9 m,and when the electrolyte concentration is higher than 0.9 m,however,the ion current growth rate deviates from linearity and tends to be slow.This is because the double layer in the channel becomes thin at high concentration,too many counter-ions accumulate near the wall,and the strong viscous resistance leads to the decrease of the electromobility of ions.When the wall Charge density of the channel increases,the ionic current increases first and then decreases.As the wall Charge density increases,more counter ions are attracted,and the strong viscous resistance of ions near the wall decreases the electromobility of ions and thus the ionic current.When the electric field intensity on the channel changes,the ion migration rate does not increase linearly with the increase of the electric field intensity because of the strong interaction between ions.Single-walled carbon nanotube(SWCNT)was added into boron nitride nanotube(BNNT)to study the effects of the volume of SWCNT,the wall Charge density,and the diameter of BNNT on the cross-hole current.The simulation results show that the volume occupancy of the single-walled carbon nanotube interferes with the directional movement of the ions,and the decrease of the axial velocity of the ions results in the decrease of the through-hole current.The increase of the charge of SWCNT will attract more counter ions to move to the center of the channel,which will lead to the increase of the velocity of ion directional movement.The mutual action of the two causes the cross-hole current to be gradually smaller than the reference current.When the diameter of the nanotube decreases,the relative thickness of the electric double layer and the nanotube increases,the effect of the electric double layer inside the channel is obvious,and the ion current increases with the increase of ion mobility on the channel surface.The P-2000 microelectrode drawing instrument was used to prepare the nanotubes,and a four-probe test rig was designed and built to study the relationship between the conductance and the concentration of sodium chloride solution in the confined nanotubes.The results show that the ionic conductivity in the channel increases linearly with the increase of solution concentration,linearly with the increase of solution concentration at0.3m-1.5m and continuously increases with the increase of solution concentration,when the concentration of the solution reaches 2.1 m,the ionic conductivity keeps stable.At the same solution concentration,the smaller the channel diameter is,the larger the conductivity is.