Simulation Of Ion Transport Properties Of Asymmetric Nanopore Based On Finite Element Method

With the rapid development of nanotechnology and micro/nanoscale processing,nanoscale material preparation technology and micro/nanoscale devices have been widely studied.Therefore,the ion transport properties and applications in nanopores have attracted much attention.Asymmetric nanopore exhibits rectification effect due to the asymmetry of nanopore properties and the asymmetry of nanopore ion solution,and salt differential energy power generation performance due to the asymmetry of nanopore ion solution.Therefore,it has great application potential in ion detection,sequencing,sensing,energy conversion and other fields.The research on the electrical properties and ion transport properties of asymmetric nanoscale channels is of great significance to expand the application field of nanochannels and improve their performance.Based on the mathematical model of Poisson Nernst Planck equations(PNP model),a nanopore simulation model is established by using finite element simulation software to explore the special ion transport properties in nanopores,providing a theoretical basis for nanopore experimental research and a certain reference for the development of new high-performance nanoscale devices.The main research contents of this paper are listed as follows:(1)The two mainstream mathematical models for simulating the ion transport properties in charged nanopores are compared.Compared with P-B model,P-N-P model is more suitable for the simulation of nanopore rectification effect and salt differential energy power generation.(2)The relationship between the structural parameters of single cone nanopores and the rectification effect of nanopores was explored.From simulation results,it can be seen that strong rectification phenomenon occurs only when the thickness of electric double layer and nanoscale pore size are equivalent to a certain extent at an appropriate concentration.In this thesis,the concentration range of simulated electrolyte solution is 0.01～1000 mol/m~3.The results show that the rectification ratio reaches the maximum value at the concentration of 0.1 mol/m~3.The rectification ratio increases with the increase of nanopore length.With the increase of the radius of the nanopore tip,the rectification ratio increases first and then decreases.The rectification ratio decreases with the increase of the half cone angle of the nanopore.(3)The effects of ion diffusion direction,nanopore wall surface charge density and electrolyte solution type on salt differential energy power generation are investigated.The results show that the salt differential energy power generation performance in conical nanopores can be improved by establishing the electrolyte concentration gradient from the base to the tip.In the study of the types of electrolyte solutions,it can be concluded that the net current of the nanopores is generated by the competition between ion migration and ion diffusion caused by the surface charge of the nanopores when the nanopores show ion selectivity.Under the condition of mutual competition,the direction of net current in the channel may be reversed.(4)A cylindrical conical double-layer nanopore is established.The effect of ion diffusion direction on its salt differential energy power generation performance is studied,and the difference between conical double-layer nanopore and single nanopore is compared.At the same time,the effects of asymmetric pore length ratio and asymmetric surface charge on its salt differential energy power generation are explored.Finally,the double-layer nanopores are introduced into parameterization to compare the power generation performance of various combined nanopores.The results show that the diffusion of ions from the cylindrical side to the conical side of the nanopores,the appropriate combination of pore length and high surface charge density can bring excellent electric energy conversion effect.With the introduction of parameterization,the geometry of nanopores changes from cylindrical bullet nanopores to cylindrical horn nanopores,the maximum output power decreases first and then increases,and the conversion efficiency increases monotonically.