Molecular Dynamics Simulation And Experimental Study On Nanotube Ion Transport And Rectification

When the pipe size is reduced to the nanometer scale,macroscopic fluid transport operation will not be fully applicable,there have been phenomena such as the rectification of ions,selectivity,and the enrichment and dissipation of ions.Grasping the mechanism and laws of these phenomena is crucial to the development of nanofluidics.In addition,understanding the impact of biomacromolecules on the ion transport properties and rectification phenomena in nanochannels is the premise basis for solving the current difficulties in practical application of nanofluidics.In response to the above problems,this article mainly develops the following aspects of research:By means of molecular dynamics simulations,the effect of nanopipe shape on ion transport at different liquid concentrations was studied.Research shows:In the same nanochannel,as the amount of ions increases with the concentration of the solution,the viscosity of the solution also becomes larger,which in turn limits the movement speed of the ions,making the growth rate of the ion current decrease.When the shape of the nano-tubes is different,due to the asymmetry of the tapered nano-tube structure,the charge on the inner wall surface will generate the inner wall bond and energy from the small end to the big end in the axial direction,thereby promoting the axial movement of the ions,making the the ionic currents in the shaped nanochannels are significantly larger than those in the tapered nanochannels,so-called signal amplification.The effect of C60 macromolecules on the ion rectification in a constrained cone-shaped nanochannel was investigated by means of molecular dynamics simulation.Research shows:When a neutral C60 molecule is transported in a tapered nanochannel,the effect of its own volume not only increases the local concentration of the solution,but also hinders the directional movement of the ions in the tube,resulting in the phenomenon that the via current is less than the reference current.When charged C60 molecules are transported in tapered nano-pipes,as their charge capacity increases.On the one hand,due to the attraction,more ions in the body fluid enter the pipeline.On the other hand,the electric field and wall charge bonds and energy that they receive are combined with the external force,and the resistance to ion movement is weakened.The superposition effect of two aspects makes the via current increase with the increase of C60 molecular charge.Compared with the C60 molecule,the charged C60 molecule is affected by its own volume,attracting ions,and external force,and thus the reference current changes from less than the via current to more than the via current as the concentration of the solution increases.In the forward and reverse electric field,the neutral C60 molecule's own volume is quite obstructive to ions,so it does not affect the rectification effect.Under positive and negative electric field,with the increase of the charge of C60 molecules,the influence of the solution concentration and the number of ions on the current increased year-on-year,and they cancel each other out.However,due to the forward stacking of the charge and energy of the wall under the positive electric field and the force of the electric field on the charged C60 molecules,the hindrance to the movement of the ions is smaller when the electric field is reversely applied.Therefore,the rectification ratio becomes larger as the charge amount of C60 molecules increases.A cone-shaped glass nanotube was prepared by a P-97 type glass microelectrode pulling apparatus,and a four-probe test stand for detecting the ionic current in the tapered nano tube was set up.The ion currents in the cone-shaped glass nanotubes at different solution concentrations were measured and the ion rectification phenomenon that occurred in the previous simulation was verified.